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1. Notes 4 Notes Notes 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Notes 6 Report Form for Problems and Solutions We have provided this form to encourage you to tell us about any difficul ties you have experienced in using your Spectra Physics instrument or its manual problems that did not require a formal call or letter to our service department but that you feel should be remedied We are always interested in improving our products and manuals and we appreciate all suggestions Thank you From Name Company or Institution Department Address Instrument Model Number Serial Number Problem Suggested Solution s Mail To FAX to Spectra Physics Inc Attention Quality Manager SSL Quality Manager 650 961 7101 1335 Terra Bella Avenue M S 15 50 Post Office Box 7013 Mountain View CA 94039 7013 U S A E mail sales splasers com www spectra physics com
2. Grating OUT Figure 4 5 Optical Design of the BWD compressor components are not shown for clarity The following indicators and connectors for the BWD are on the SDG II PD PD indicators front panel when both lamps are on indicate the stretcher is spreading the seed pulse spectrum properly on the tall stretcher end mirror PD represents the red end of the spectrum PD represents the blue end If a lamp is off the corresponding photodetector is receiving a signal below threshold RESET button front panel when pressed resets the relay and resumes Spitfire amplification after the underlying problem is resolved and both BWD lamps are on BWD connector 4 pin 12 mm back panel connects to the BWD photodiodes via a similar connector on the Spitfire BWD ON switch back panel when in the down position disables the BWD and allows the amplifier to function regardless of spectrum spread Disabling the BWD can result in permanent damage to the Spitfire Back Panel Note Controls Indicators and Connections POWER CONNECTOR BWD CONNECTOR INTERLOCK CONNECTOR and SWITCH and SWITCH and SWITCH gt 3 Zz O 2 gt o FP RF SYNC TRIGGER IN TRIGGER OUT H V 1 HV2 RS 232 RF TRIGGER TRIGGER SYNC IN OUT Figure 4 6 SDG II Back Panel Power connector and switch 110 220 Vac are the primary power in put for the SDG IT The unit includes EMI protection a Y2 amp fuse and an on of
3. Do not touch Appropriate laser safety eyewear should be worn during this opera tion Refer to the manual before operating or using this device xiii Standard Units The following units abbreviations and prefixes are used in this Spectra Physics manual Quantity Unit Abbreviation mass kilogram kg length meter time second Ss frequency hertz Hz force newton N energy joule J power watt W electric current ampere A electric charge coulomb C electric potential volt V resistance ohm Q inductance henry H magnetic flux weber Wb magnetic flux density tesla T luminous intensity candela cd temperature celcius C pressure pascal Pa capacitance farad F angle radian rad Prefixes tera 10 T deci 101 d nano 10 n giga 10 G centi 107 c pico 1077 p mega 10 M mill 10 m femto 1015 f kilo 10 k micro 105 y atto 10 a XV Appreviations The following is a list of abbreviations used in Spectra Physics manuals ac AOM APM AR BI FI CDRH CE CPM CW dc E O fs GTI GVD HR IR oc PS PZT RF SBR SCFH SPM TEM TI SAPPHIRE UV alternating current acousto optic modulator active pulse mode locking anti reflection birefringent filter Center of Devices and Radiological Health European Union colliding pulse mode locking continuous wave direct current electro optic femtosecond or 10 second Gires Toutnois Interferometer group velocity dispersi
4. tics and by using Pockels cells to control this polarization A Pockels cell is an electro optic device that without an applied voltage has essentially no effect on light transmitted through it With an applied voltage however the crystalline material in a Pockels cell acts as a 4 waveplate that rotates the polarization of transmitted light by 45 each time a pulse passes through it If a light beam passes through an active Pockels cell twice passes through the cell and is then reflected back through it again the polarization of the beam is rotated by 90 or from horizontal to vertical or vice versa How ever in order for this to work well the Pockels cell must be properly aligned with no voltage applied Likewise the applied voltage must be cali brated to achieve the precise degree of polarization rotation The input Pockels cell is paired with a passive 4 waveplate and the optical path is designed so that the beam makes a double pass through this combi nation When the cell is off the double pass through the passive 1 4 wave plate will flip the beam polarization 90 when the cell is on the beam experiences a double pass through two 4 waveplates leaving its polariza tion unchanged The Spitfire cavity is designed so that horizontally polarized light remains trapped in the cavity and is amplified Details of how the input Pockels cell combines with the cavity optics to select a pulse for amplification are given in Chapter
5. 3 Output energy per pulse applies between 780 and 800 nm For higher energy output systems please contact Spectra Physics Pulse width applies at the peak wavelength and requires the seed laser performance specified for the Amplifier model A Gaussian pulse shape 0 7 deconvolution factor is used to determine the pulse width FWHM from an autocorrelation signal as measured with a Spectra Physics Model SSA current version Contrast ratio is defined as the ratio between the peak intensity of the output pulse to the peak intensity of any pulse that occurs more than I ns before the output pulse The con trast ratio for any pulse more than I ns after the output pulse post pulse contrast ratio is gt 100 1 For higher performance please contact Spectra Physics Wavelength the system is tunable from 750 to 840 nm without an optics change To cover the 840 900 nm region separate optics are required for both I K and 5 K sys tems For other wavelengths and for second and third harmonic generation please con tact Spectra Physics N A n Table 3 2 Spitfire Specifications Common to All Models Beam Beam Transform Energy Output Diameter Divergence Limit Stability Polarization 7 mm lt 1 5 lt 1 5 lt 3 horizontal 1 Nominal beam diameter at e points Beam divergence as a multiple of diffraction limit Assuming seed pulses are transform limited Gaussian temporal pulses t Applies at peak wavelength between 780
6. After adjusting the seed laser re check the beam pattern If the pattern shown in Figure C 1 cannot be obtained the stretcher may need to be realigned This procedure is beyond the scope of this manual Contact Spectra Physics for assistance The output beam from the stretcher should now be picked off by mir ror M It may be necessary to slightly adjust the vertical tilt of the large gold mirror M using the adjustment described in Chapter 7 Stretcher and Compressor Beam Paths Re check the alignment of the beam into the regenerative amplifier Compressor Alignment Check The alignment of the beam through the compressor should not have changed since the Spitfire was last operated but check it anyway Verify the output beam is round and even in intensity Use an IR viewer to look at the compressor grating The pattern shown in Figure C 2 should be evident Figure C 2 Radiation Patterns on Compressor Gratings C 3 Spitfire Ti Sapphire Regenerative Amplifer Systems Pump Beam Alignment Once the Spitfire system has been properly installed the alignment of the pump laser into the Spitfire amplifier should not need to be adjusted during normal operation Some circumstances however such as maintenance or service of the pump laser may require aligning the pump beam The most common symptom of pump beam misalignment is poor Spitfire mode qual ity that results when there is poor superposition of the pump beam mode in the Ti
7. As part of the alignment procedure the Spitfire is sometimes operated as a laser rather than as a regenerative amplifier Spitfire Ti Sapphire Regenerative Amplifer Systems The Synchronization and Delay Generator SDG II 3 10 Note The Synchronization and Delay Generator or SDG II provides the timing needed to synchronize the Pockels cells to the passage of the pulses through the amplifier This allows the Pockels cells to first capture pulses and then later to direct them into the compressor This timing includes synchronization to the seed and pump lasers The SDG II also provides an adjustable delay based on the output of the Spitfire that allows laboratory instruments to be synchronized to the arrival of pulses at the target Immediately after the Ti sapphire rod is excited by a pulse from the pump laser the input Pockels cell confines a selected pulse in the amplifier and sends it into the rod for amplification The input Pockels cell therefore must be synchronized to the mode locked pulse train after the next avail able pump pulse and remain synchronized after each pump pulse To achieve this the input Pockels cell is locked to the RF signal generated by the modelocker in the seed laser Additionally the Pockels cell firing phase the delay is adjustable to allow the synchronization to be opti mized This ensures that the input Pockels cell fires only after the selected pulse has passed completely through it The outp
8. Note A typical laser amplifies the spontaneous emission randomly present in its own gain medium in order to initiate lasing Regenerative amplifiers on the other hand are designed to recirculate and amplify low energy laser pulses from a separate seed laser and are an efficient means of generating high peak power pulses Thus instead of allowing the energy in the amplifier crystal to escape as random spontaneous emission these seed pulses hav ing an energy that exceeds the spontaneous emission energy are selec tively amplified The Spitfire can be thought of as a Q switched cavity dumped Ti sapphire laser that is configured to operate as an amplifier Here is how it works As explained earlier Ti sapphire has a broad gain bandwidth that is neces sary for the production and amplification of sub picosecond pulses In addition a Ti sapphire amplifier has a high saturation threshold that makes it possible to extract relatively high energies from a system of moderate size A single pass of a very low energy sub picosecond pulse through a Ti sap phire amplifier will increase the pulse energy typically by a factor of about 3 or 4 However the stimulated emission that provides this gain draws down the population inversion in the gain media only a small amount in a single pass thus allowing the gain media to remain well below the threshold at which stimulated emission will reverse the population inversion that is saturate the gain
9. The Spitfire can be controlled by a computer via the RS 232 interface on the SDG II Appendix A provides information regarding the command lan guage used by this system Spitfire Head External Controls Pump Input End Panel Pump Laser Input Port DA Figure 4 1 Spitfire Panel Pump Input End Pump laser input port is the input port for the beam from the pump laser e g a Spectra Physics Evolution Q switched laser 4 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Seed Input Side Panel HSD 1 HSD2 HV1 HV2 Seed Laser Input Port Spitfire io o lO 7 Cooling Water BWD OUT DC MOTOR oio Figure 4 2 Spitfire Panel Seed Laser Input Side Seed laser input port provides an input port for the seed beam Tsunami or Mai Tai mode locked laser HV 1 connector MHV HIGH VOLTAGE connects via a high voltage cable to the 1 6 kVdc H V 1 output connector on the back of the SDG H 1 kHz systems or to the auxiliary power supply 5 kHz systems for driv ing the input Pockels cell HV 2 connector MHV HIGH VOLTAGE connects via a high voltage cable to the 1 6 kVdc H V 2 output connector on the back of the SDG II 1 kHz systems or to the auxiliary power supply 5 kHz systems for driv ing the output Pockels cell HSD 1 connector BNC connects to the OUT 1 DELAY connector on the front of the SDG II for triggering the input Pock
10. The reduction factor is not shown only the actual output repetition rate is displayed SYNC ENABLE control selects synchronized LED is on or unsynchro nized LED is off mode If both the LED and error lamp are on the sync source is absent or the seed laser has stopped modelocking Pressing the SYNC ENABLE button again turning off the LED will correct the error con dition but it will also disable the synchronization function of the SDG II Synchronized mode allows the sync outputs to fire based on the current pump laser delay setting OUT 1 DELAY and the next available seed pulse Controls Indicators and Connections It provides a way to fire the input Pockels cell based on sync signals from two circuits the pump laser Q switch signal and the seed laser pulse train SYNC ERROR indicator when on and the SDG II is in synchronized mode indicates the sync signal is absent or the seed laser is not mode locked BWD PD PD and RESET see Bandwidth Detector on page 4 6 MODE control selects CONTINUOUS repetition rate firing based on input trigger or SINGLE SHOT firing the corresponding LED turns on MAN TRIG control causes the three output triggers to fire a single pulse when the firing mode is set to SINGLE SHOT and the button is pressed ENABLE controls 3 turn the three adjustable output trigger signals on and off If a signal is enabled its corresponding LED is illuminated When disabled only that
11. 7 The output Pockels cell works in conjunction with the polarizer in the amplifier cavity to release an amplified pulse at a time determined by the SDG II Details of how the timing is set for ejecting an amplified pulse are given in the section The Synchronization and Delay Generator SDG II on page 3 10 One measure of the quality of pulse selection is given by the contrast ratio the factor by which the amplifier output power exceeds the power in spurious pulses which are always present to some degree before or after the main true pulse The value of the contrast ratio is determined by the quality of the 4 waveplates the activation time of the Pockels cells their intrinsic birefringence and their drive electronics The components selected for the Spitfire that affect contrast ratio are of the highest quality available As a consequence the limiting factor for contrast ratio is the natural birefringence of Pockels cells This birefringence results in an optical rise time that is less than a nanosecond The net effect is high contrast ratios and excellent suppression of spurious pulses The 3500 V applied to the Spitfire Pockels cells is provided by two high voltage power supplies For 1 kHz systems these power supplies are in the SDG II An auxiliary high voltage power supply is provided for 5 kHz systems The Pockels cells themselves are in the Spitfire amplifier General Description Regenerative Amplification
12. M 4 etc The beam path is shown in Figure 7 7 For clarity some components such as apertures and lenses are not shown The Seed Beam Path 1 Horizontally polarized pulses from the stretcher are rotated 1 to ver tical polarization by the polarization rotating periscope PS and are directed into the amplifier cavity by mirror M 2 2 The Ti sapphire rod cut at Brewster s angle for horizontally polarized light reflects the vertically polarized pulses off its surface 3 and directs them to the first cavity mirror CM 4 which directs the pulses to the input Pockels cell At this point the pulsed beam is in the amplifier cavity Whether a particular pulse remains in the cavity to be amplified is deter mined by the input Pockels cell When this Pockels cell is off it is transpar ent to both vertically polarized and horizontally polarized light When the input Pockels cell is on combined with the 4 waveplate 4 it rotates the polarization of the beam 90 Spitfire Ti Sapphire Regenerative Amplifer Systems Note One of three things will now happen Case a the input Pockels cell is off when the pulse arrives the pulse passes through the cell and is reflected back to the same Pockels cell If this Pockels cell is still off when the pulse returns the pulse is rejected after one round trip through the amplifier Case b the input Pockels cell is on when the pulse arrives the pulse is n
13. RS 232 Communication Protocols The following protocols must be set in the communication software used to control the SDG II Setting Value Rate 9600 bps Data Bits 8 Parity None Stop Bits 1 Flow Control None A 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Command Query Response Format All SDG IT RS 232 commands queries and responses are in ASCII format and each command or query must be terminated with a carriage return lt cR gt Commands that have a numerical argument must be sent with all the digits preceded with zeros if necessary Commands must all be in lower case All queries end with a question mark Valid queries return data followed by a carriage return Valid com mands return the string Ok Invalid commands or queries return the string Bad Table A 1 Quick Command Reference Guide Command Parameter Function status none Returns the overall status of the SDG II see below set cN O 1 Enables 1 or disables 0 the output on channel N 1 3 read cN none Returns the output state of chan nel N 1 3 set del cN 0000 0 to 1275 0 Sets the delay for channel N 1 3 in nanoseconds read del cN none Returns the delay for channel N 1 3 in nanoseconds set rate 0001 0002 etc Sets the trigger rate divisor read rate none Returns the trigger rate divisor read bwd none Returns the state of the BWD latching interlock reset bwd none Resets the BWD lat
14. and 800 nm Spitfire Ti Sapphire Regenerative Amplifer Systems Outline Drawings Pump End Output End 5 0 CC 12 7 CC OA yy QA QA al 475 F 475 16 2 121 12 4 l 7 50 19 1 18 25 one in inches EK A AAA All dimensions in omn 46 4 24 00 gt 61 0 14 3 5 Seed Input Side 9 25 x A ens 23 5 S Spectra Physics Spitfire aa 7 ri l 2 25 111 a 28 2 i L L in gt L cm Model L in L cm Spitfire F P PM amp USF 48 0 121 9 Spitfire 50FS 60 0 152 4 Figure 3 5 Spitfire Outline Drawing E 13 0 ia 12 0 E 33 0 30 5 O i 0 0 0 23 S Spectra Physics Oo CI Py LI TI Figure 3 6 SDG IT Outline Drawing 3 12 Chapter 4 Controls Indicators and Connections This chapter describes the controls indicators and connections needed to operate the Spitfire system It describes the external panels of the Spitfire amplifier the synchronous delay generator SDG II and auxiliary connec tions Occasionally troubleshooting or optimizing system performance may require adjustment of the optical components inside the Spitfire amplifier The internal adjustments for aligning the optical path inside the Spitfire are described separately in Chapter 7
15. and PD where O 0ff and 1 on The third value is the state of the 5 Vdc interlock where O latched and 1 clear For example 110 indicates that PD and PD are illuminated but the 5 Vdc interlock is latched preventing output set rf Sets the state of the RF sync to be enabled 1 or disabled 0 read rf Returns the state of the RF sync as enabled 1 or disabled 0 set mode Sets the output trigger mode to continuous 0 or single shot 1 read mode Returns the output trigger mode as continuous 0 or single shot 1 man trig Executes a single output event when the SDG II is in single shot mode RS 232 Interface Limitations of RS 232 Control of the SDG Il The following functions cannot be accessed with RS 232 commands e The value in the Trigger Frequency display cannot be read e The status of the Sync Enable Error LED cannot be read e The state set by the BWD on off mechanical switch cannot be changed e The state set by the Interlock enable disable mechanical switch cannot be changed Typical Command Usage The following scenario illustrates a simple control sequence when using the RS 232 command language with the SDG IT 1 Turn on the system then wait at least 5 seconds for the SDG II to ini tialize status Determine the state of the SDG II set cN Enable the required outputs set del cN Set the required delay values set rate Set the output trigger frequency reset bwd If all i
16. chiller for the Mai Tai or Tsunami laser is shared by the amplifier rod This provides adequate thermal protection for the rod The water flow to the amplifier is in series downstream from the Mai Tai or Tsunami as shown in Figure 5 3 Mai Tai or Tsunami Seed Laser Out Spitfire Regenerative Amplifier Chiller Figure 5 3 Serial Connections for Chiller Water Spitfire Ti Sapphire Regenerative Amplifer Systems Chapter 6 A Eyewear Required Operation Laser radiation is present Safety glasses of OD 4 or greater at all lasing wavelengths must be worn at all times when operating this laser system Refer to Appendix A for information about controlling the system via com puter using the RS 232 interface on the SDG II It is recommended that the following equipment be kept on hand Start up Procedure Warning Y a power meter capable of measuring between 10 mW and 20 W aver age power from 527 nm to 900 nm a fast photodiode with a 2 ns rise time or better a fast CRT analog oscilloscope capable of 300 MHz or better IR viewer and IR card an autocorrelator e g Spectra Physics SSA Inspect the optic surfaces before the Spitfire is turned on and blow off any dust with dry nitrogen Clean the optics as necessary Except for blowing off dust with dry nitrogen the gratings and the gold coated mirror cannot be cleaned Attempting to clean these components will
17. described in the sections that began this chapter In many installations however only a mode locked femtosecond laser such as the femtosecond Tsunami is available to seed the Spitfire ampli fier The Spitfire PM pico mask system allows you to produce ampli fied picosecond pulses using the femtosecond seed laser This config uration has specific advantages for certain applications such as pumping an optical parametric amplifier The Spitfire PM converts the pulse spec trum of the femtosecond seed pulses into a spectrum that is equivalent to that produced by a picosecond seed laser Recall the relationship between laser pulse width and bandwidth described in Chirped Pulse Amplification a very short pulse exhibits a broad spec trum longer pulses exhibit narrower spectra Since the pulse stretcher works by spatially separating the spectrum of the seed pulses the band width of these pulses will be reduced if part of this spectrum is discarded When the pulse is later compressed its duration will be longer than if the entire spectrum had been preserved The Spitfire PM accomplishes this in a conceptually straightforward man ner A femtosecond seed pulse enters a stretcher that uses a grating designed for picosecond operation The spatially spread pulse is then directed onto an aperture that is precisely aligned to mask part of the spec trum that reflects from the grating and a portion of the spectrum is allowed to pass thr
18. mirror PM has vertical and horizontal adjustments PL focuses the pump beam in the Ti sapphire rod The lens mount has ver tical and horizontal adjustments as well as movement in the direction of the beam to focus it The 527 nm green light from the Nd YLF pump laser is horizontally polarized allowing it to enter and be absorbed by the Ti sapphire rod Roughly 80 of the pump beam is absorbed by the rod The fraction of the high power pump beam that is not absorbed by the Ti sapphire rod transmits through the rod onto CM CM does not reflect a significant amount of 527 nm light and instead allows it to pass through where it is absorbed by the beam dump behind it Chapter 8 Required Try This First a Eyewear Maintenance and Troubleshooting Exceptional care must be taken when operating the Spitfire with the cov ers removed Laser protective eyewear must be worn to protect the eyes from all wavelength emissions If the Spitfire is producing pulses but performance has degraded first verify the following e the BWD interlock is properly set e the seed laser is operating properly and its shutter is open e the pump laser is operating properly and its shutter is open e the pump beam routing mirror PM is properly set If the components above are operating properly you may only need to adjust the pump power or pump beam routing mirror PM to optimize out put Refer to Appendix C before attempting these adju
19. other lasers it requires no safety interlocks or emission indi cator All safety interlocks and emission indicators are associated with the pump and seed lasers When both the pump and seed lasers are disabled the Spitfire is disabled Any electronic product radiation except laser radiation emitted by a laser product as a result of or necessary for the operation of a laser incorporated into that product Laser Safety Fuses The Spitfire SDG II controller uses one of the following fuses as appropri ate for the local line voltage 120 Vac 220 Vac F1AH 250 V Slow Blow FO 5AH 250 V Slow Blow Maximum Emission Levels The following is the maximum emission level possible for the Spitfire amplifier Use this information for selecting appropriate laser safety eye wear and implementing appropriate safety procedures This value does not imply actual system power or specifications Emission Wavelength Maximum Power 690 to 1080 nm 10 W CDRH Compliance This laser product complies with Title 21 of the United States Code of Fed eral Regulations Chapter 1 subchapter J parts 1040 10 and 1040 11 as applicable To maintain compliance with these regulations once a year or whenever the product has been subjected to adverse environmental condi tions e g fire flood mechanical shock spilled solvent etc check to see that all features of the product identified on the CDRH Radiation Control Drawing found late
20. result in permanent damage Turn on the seed laser system Mai Tai or Tsunami including the chiller as described in its user s manual Check the alignment of the mode locked beam into the Spitfire Opti mize the alignment if necessary following the procedure below Seed Beam Alignment into the Regenerative Amplifier Turn on the SDG II Push the reset button on the front panel for the BWD interlock If the seed laser is properly mode locked both BWD LEDs will be lit Refer to the procedures in Chapter 8 Maintenance and Troubleshooting if the LEDs indicate a problem one or both are not on Enable OUT 1 DELAY and OUT 2 DELAY on the SDG II Turn on the pump laser Evolution as described in the user manual that accompanies it Allow for the specified warm up period 6 1 Spitfire Ti Sapphire Regenerative Amplifer Systems 6 Adjust the Spitfire repetition rate using the INPUT DIVIDE control on the SDG II if so desired Optimizing Pulse Compression Temperature changes or similar variations in the environment of the Spitfire may require adjusting the compressor to optimize the pulsed output Use the Motion Controller to set the compressor length for optimum com pression This adjustment is critical for femtosecond operation the length must be within about 0 1 mm of the optimum The best way to set the com pressor length is to monitor the pulse width using an autocorrelator while using the Motion Controller
21. sapphire rod Refer to Chapter 7 for a description of the optical design shown in Figure C 3 PM2 PL3 ee on f a l CM4 A CM3 ann iP Rod Telescope KN gt y 0 CMa CM F Beam y 7 Regenerative Amplifier Cavity Dum 527 nm PL PL2 PM p Figure C 3 Pump Beam Path of the Spitfire 1 Record the pump beam power required to operate the Spitfire Block the seed pulses into the Spitfire 3 Adjust the pump laser Evolution power to the minimum power that allows a stable green beam to be observed Verify the pump beam passes through the input port without clipping 5 Adjust the pump beam to center it on the lenses of the zoom telescope PL and PL and also on PM Adjust PM to center the beam on PM Adjust PM to center the beam in the Ti sapphire rod The beam should be 1 to 2 mm from the edge of mirror CM If this is not the case make small adjustments to PM as needed 9 When the pump beam is centered on the Ti sapphire rod it should pass through the center of PL If it does not loosen the screw holding the mount for PL to the chassis and position it so that it does Be sure to maintain the distance from the lens to the face of the Ti sapphire rod If moving PL moves the pump beam on the rod use PL to re center it Iterate adjustment of PL and PL until the beam is centered on both PL and the rod Note that having the correct distance from PL to the Ti sapphire rod is particularly important for
22. so that the pulse train moves to the left on the oscilloscope screen Next enable and adjust the SDG II OUT 2 DELAY until the intracavity pulse train looks like that shown in Figure 6 5 Note that the most sta ble performance is obtained by adjusting the timing so that the pulse train includes the one pulse that is just past the maximum Figure 6 5 Intracavity Pulse Train with the Timing Set Correctly 8 10 Set up a fast photodiode to sample the output of the Spitfire and view the output pulse on the oscilloscope Use the same settings given in Step 4 A single stable output pulse should be displayed Observe the output mode If adjustment is necessary refer to the pump beam alignment procedure in Appendix C If the pulse amplitude is stable but there is evidence of a secondary pulse make a slight adjustment to the OUT 2 DELAY control If this does not produce a single stable cavity dumped pulse adjust OUT 1 DELAY by 10 ns If this procedure does not produce a single stable cavity dumped pulse re check and adjust the intracavity Q switched pulse i e block the seed laser beam again If a single stable pulse is still not produced contact your Spectra Physics service engineer Re Optimization Operation A change in room temperature or similar environmental factors may make re optimization necessary To do this 1 Disable OUT 2 DELAY on the SDG II and monitor the intracavity pulse as
23. the speed for the compressor motor micrometer when either the REV or FWD buttons are pushed REV button moves the stretcher to shorten the beam path in the com pressor FWD button moves the stretcher to lengthen the beam path in the com pressor ON OFF switch turns the controller on and off To save the battery always leave the switch in the OFF position when the controller is not in use Chapter 5 Caution W Preparing for Installation Call your Spectra Physics service representative to arrange an installa tion appointment which is part of your purchase agreement Allow only authorized Spectra Physics representatives to install your Spitfire system You will be charged for repair of any damage incurred if you attempt to install the Spitfire yourself and such action may void your warranty System Components Note Because a typical Spitfire installation requires both a pump laser and a seed laser in addition to the Spitfire some planning is required before beginning installation Typical system components include Evolution a multi kilohertz intracavity doubled diode pumped Nd YLF pump laser and a e Mai Tai femtosecond Ti sapphire modelocked seed laser this system includes its own internal diode pumped CW pump laser ora e Tsunami femtosecond or picosecond Ti sapphire mode locked seed laser and a e Millennia diode pumped CW laser for pumping the Tsunami Although not recomme
24. time the user can send a trigger signal to a device such as an oscilloscope that is part of the target apparatus The control knob adjusts the delay in 250 ps increments or 10 ns incre ments if the knob is pushed in during adjustment The corresponding BNC connector connects to the user s oscilloscope for monitoring pulses or to other apparatus of the target or data acquisition system 4 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Bandwidth Detector Warning m The Bandwidth Detector BWD protects the regenerative amplifier optics from damage if the stretcher cannot adequately reduce the peak power of the seed pulses before they are amplified This can happen for example if a portion of the beam in the stretcher is blocked When the seed laser is stable and properly mode locked the BWD permits the SDG II to function normally When the BWD senses a lack of signal a relay will disable the trigger signal that fires the Pockels cells No pulses are selected for amplification thus protecting the optical components The BWD relies on the signals from two fast photodetectors placed behind the tall stretcher end mirror This mirror transmits about 5 of the incident light to the detectors If the signal from either detector falls below a thresh old factory set for each version of the Spitfire the BWD is activated Photodiodes De PD Red Vertical Retroflector er E PD Blue ze Tall Stretcher End Mirror
25. to adjust the horizontal retroreflector The compressed pulse should look like that shown in Figure 6 1 At 038 U i 2 0 3 545 A A A i E PR Figure 6 1 Autocorrelation of a Well Compressed Pulse If you do not have access to an autocorrelator optimize the pulse length by observing the output on a white business card When the compressor length 1s correct the beam on the card will appear blue in the center due to high peak power frequency doubling in the treated paper Shut down Procedure 1 Before shutting down enter Spitfire output power into a system log along with the level of the pump laser and the timing parameters of the SDG II Disable OUT 1 DELAY and OUT 2 DELAY 3 Power down the SDG II Turn off the pump laser Evolution as described in its user s manual Note that the chiller must remain on if the Evolution power supply is left on 5 Power down the seed laser Mai Tai or Tsunami as described in their user s manual The chiller for the seed laser should always remain on Operation Basic Performance Optimization In addition to optimizing the optical length of the compressor as described in the previous section the parameters that should be optimized are e stability of the seed pulses e seed beam alignment into the regenerative amplifier e beam uniformity e build up reduction time optimizing the regenerative amplifier These parameters should not need to be checked or optimized on a dai
26. 013 VISIBLE AND OR INVISIBLE LASER RADIATION MT VIEW CALIFORNIA 94039 7013 AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION MANUFACTURED CLASS IV LASER RODCUT MONTH YR WAVELENGTH 700 1000nm MODEL a THIS LASER PRODUCT COMPLIES PULSE LENGTH 30fs 6ps zieken WITH 21 CFR 1040 AS APPLICABLE MADE IN U S A CE Warning Label 1 Identification Certification Label 2 AVOID EXPOSURE VISIBLE AND OR INVISIBLE LASER RADIATION VISIBLE AND OR CAUTION WHEN OPEN AND INTERLOCK DEFEATED INVISIBLE LASER VISIBLE INVISIBLE AND AVOID EYE OR SKIN EXPOSURE TO DIRECT RADIATION IS EMITTED RF ELECTROMAGNETIC OR SCATTERED RADIATION FROM THIS APERTURE RADIATION WHEN OPEN CLASS IV LASER PRODUCT din CE Aperture Label 3 Caution Label Danger Interlocked Housing Label 5 Part 1 RF Energy Present 4 CE Aperture Label 6 CE Caution Label 7 CE Electrical Warning Label 8 Part 2 220 Volts ONLY CE 110 Volts ONLY CE Certification Label 9 Voltage Input Label 10 Figure 2 4 CE CDRH Warning Labels Spitfire Ti Sapphire Regenerative Amplifer Systems Label Translations For safety the following translations are provided for non English speak ing personnel The number in parenthesis in the first column corresponds to the label number listed on the previous page Table 2 1 Label Translations Label French German Spanish Dutch CE Rayonnement visible Austrit
27. 2 8 Sources for Additional Information nen eee eee eeen 2 9 Laser Safety Standards neee eee eeen 2 9 Equipment and Training a ae cta a tee ete le baled thd bane boda dea ee ets 2 10 vii Spitfire Ti Sapphire Regenerative Amplifer Systems Chapter 3 General Description cece eee eee eee eee 3 1 TRS AP PMS etend wee deca ern isd ee keen bye ace re Su ala ge ad 3 1 Chirped Pulse Amplification eenen eneen 3 3 FOW IE WOrKS ne nes bite aa NN tel oa Uh tk Ae Social ete Neenee dear le Muth 3 3 Pulse Stretching and Compression enden eneen 3 4 The Spitfire Pulse Stretcher and Compressor onee 3 5 The Spitfire 50FS Compressor Stretcher Design ae 3 6 The Spitfire PM Compressor Stretcher Design neee 3 7 Pulse Selection and Pockels Cells onee en 3 8 Regenerative Amplification neee 3 9 The Synchronization and Delay Generator SDG II een 3 10 Specifications sanat Ada A o ds 3 11 Outline Drawings anar enen A A A a Bee ae ee 3 12 Chapter 4 Controls Indicators and ConnectionS oooooooonmmm 4 1 Spitfire Head External Controls o ooococcoccooo 4 1 Pump Input End Panel 5 zaai vendre ee tad nederl oda ate ayer id 4 1 Seed Input Side Paneli ann perte acta med ene Ye ee OE He els 4 2 OQ tp t End Panel eat nne sense E anti eee dn ORM eee eee ke 4 3 The Synchronous Delay Generator eene eeen 4 3 Front Panel sont erase wales Shes e eben dak re ean a tate ERE aid 4 4 Bandwidthi
28. Detector us ey neces varend Be Dee eae Da wa a ed ee DE ED 4 6 Back Panel sns dre ae EA EE nae eenn eed 4 7 Motion Controler wa Suneoat eraa Phen ee bole weeded en week Thats pounds od ae dee 4 8 Chapter 5 Preparing for Installation 0 cee 5 1 System Components co 5 1 Pump Laser on oat ene n arten Wint de ee a A a ate ee a td E 5 2 Modelocked Seed Laser enen eneen 5 2 Preparations i Antenne A ande te Wat et A ad ae Bin dna le and 5 3 Location and Layout eeen 5 3 Required Utilities aren oeren eerie aten ee enden den dee a de led edn 4 5 3 Recommended Diagnostic Equipment eee 5 4 Tools Requited nn anr oe oe ermee en teeven a We eee AE ae AE ar ren are d 5 4 Interconnect Diagrams neee 5 5 Ghiller Zanten ie nan Dl Ses EE EE PO Beh Dee eee 5 7 Chapter 6 Operation nnen rende ews ais e ae EE 6 1 start up Procedures sar saws pen Ded bene hea vett lo Vac thd Watten 6 1 Optimizing Pulse Compression venen eneen 6 2 Shutdown Procedure se sum rn deens nen ae ele Dein aed a B Ue earn 6 2 Basic Performance Optimization eenen ene 6 3 Stability of the Seed Pulses eneen 6 3 Seed Beam Alignment into the Regenerative Amplifier oen 6 3 Beam Uniformity ns rn tee gam si seren Zaak daa DR men de he ed Rl WEEER zend 6 4 Optimizing the Regenerative Amplifier onee eee 6 5 Re Optimization ct san ara las da blend bhatt os eon ts Vi ae lat a ned 6 7 Chapter 7 The Spitfire Beam Path ooooooooomonn
29. F Radiated IEC 801 4 Fast Transients I the undersigned hereby declare that the equipment specified above con forms to the above Directives and Standards Bruce Craig Vice President and General Manager Spectra Physics Laser Group April 5 2002 Mountain View California USA 2 7 Spitfire Ti Sapphire Regenerative Amplifer Systems CE Declaration of Conformity Low Voltage 2 8 We Spectra Physics Inc Industrial and Scientific Lasers 1330 Terra Bella Avenue P O Box 7013 Mountain View CA 94039 7013 United States of America declare under sole responsibility that the Spitfire Multi Kilohertz Ti Sapphire Regenerative Amplifier System with SDG II Controller meets the intent of Directive 73 23 EEC the Low Voltage directive Compliance was demonstrated to the following specifications as listed in the official Journal of the European Communities EN 61010 1 1993 Safety Requirements for Electrical Equipment for Measurement Control and Laboratory use EN 60825 1 1993 Safety for Laser Products I the undersigned hereby declare that the equipment specified above con forms to the above Directives and Standards Bruce Craig Vice President and General Manager Spectra Physics Laser Group April 5 2002 Mountain View California USA Laser Safety Sources for Additional Information The following are some sources for additional information on laser safety standards safety equipment and t
30. PM USF and 50FS nnen 1 3 Figure 2 1 These CE and CDRH standard safety warning labels would be appropriate for use as entry warning signs EN 60825 1 ANSI Z136 1 Section 4 7 dee 2 2 Figure 2 2 Folded Metal Beam Target eee 2 2 Figure 2 3 CE CDRH Radiation Control Drawing enen 2 4 Figure 2 4 CE CDRH Warning Labels annen eneen eee 2 5 Figure 3 1 Energy Level Structure of Ti Sapphire nennen eee 3 1 Figure 3 2 Absorption and Emission Spectra of Ti Sapphire senen 3 2 Figure 3 3 The Principle of Chirped Pulse Amplification eneen enen eeen 3 4 Figure 3 4 Principle of pulse stretching using negative GVD nnee 3 5 Figure 3 5 Spitfire Outline Drawing enen ene 3 12 Figure 3 6 SDG II Outline Drawing eenen ene 3 12 Figure 4 1 Spitfire Panel Pump Input End nnee 4 1 Figure 4 2 Spitfire Panel Seed Laser Input Side neee 4 2 Figure 4 3 Spitfire Panel Output End enen eneen 4 3 Figure 4 4 SDG Il Front Panel eneen eee 4 4 Figure 4 5 Optical Design of the BWD compressor components are not shown for clarity 4 6 Figure 4 6 SDG Il Back Panel enen eenen 4 7 Figure 4 7 Motion Controller model may vary eneen eee 4 8 Figure 5 1 Spitfire Interconnect Diagram 1 KHZ neee 5 5 Figure 5 2 Spitfire Interconnect Diagram 5 KHZ neee 5 6 Figure 5 3 Serial Connections for Chiller Water 0 00000 cece tees 5 7 Figure 6 1 Autocorrelation of a Well Compressed Pulse nennen 6 2 Figure 6 2 Optical
31. Path for Seed Beam Alignment eenen eenen 6 3 Figure 6 3 Appearance of Q switched Pulse oane 6 5 Figure 6 4 Intracavity Pulse Train ene 6 6 Figure 6 5 Intracavity Pulse Train with the Timing Set Correctly 0 00 0c eee eeaee 6 6 Figure 7 1 Optical Components in the Spitfire F Stretcher and Compressor 7 2 Figure 7 2 Spitfire F Stretcher Beam Path enen enen eneen 7 3 Figure 7 3 Spitfire F Compressor Beam Path nen 7 4 Figure 7 4 Modifications for the Spitfire P enen eee 7 5 Figure 7 5 Spitfire 50FS Stretcher and Compressor Beam Path eneen 7 6 Figure 7 6 Regenerative Amplifier Optical Components aaneen eee 7 7 Figure 7 7 Regenerative Amplifier Beam Path neee 7 7 Figure 7 8 Pump Beam Path neee 7 10 Figure B 1 Stretcher Mask aaneen eene B 2 Figure B 2 Modifications to the Stretcher for PicoMask Operation neen B 2 Figure B 3 PicoMask Assembly Mounting neee B 3 Figure B 4 Rotation Stage Picosecond Configuration oococcococococ B 4 Figure B 5 Rotation Stage Femtosecond Configuration 00 0 cece eee B 4 Figure B 6 Adjustment Screws for the BWD Photodiodes nnen eneen en B 5 Figure C 1 Radiation Patterns on Stretcher Gratings eneen C 3 Figure C 2 Radiation Patterns on Compressor Gratings onee eee C 3 Figure C 3 Pump Beam Path of the Spitfire eneen C 4 Figure C 4 Alignment of beam into the compressor eene C 6 Table of Contents List of Tables Table 1 1 Spitfire Configur
32. SM all have vertical and horizontal adjustments 1 Verify the pump beam shuttered is closed 2 Check the alignment of the seed beam through apertures A and A and make small adjustments as necessary 3 Rotate the gratings out of the beam path and use the IR card to verify the beam is well aligned through the apertures not shown at the entrance to the stretcher and the exit from the compressor 4 Rotate the gratings to their original positions to resume normal opera tion The 1 order diffracted beam should strike the center of gold mir ror M 5 Check the alignment of the seed beam into the amplifier It is possible that the seed beam will have drifted slightly since the Spitfire was last operated The beam should be aligned using mirrors M and M so that it is centered on the input Pockels cell and then onto cavity mirror CM 6 Enough of the beam should pass back through the input Pockels cell the Ti sapphire rod and the other components in the optical path so that it is visible on the IR card in front of cavity mirror CM Use the IR card to make slight adjustments to mirror M4 not the cavity mirrors until you see a beam at CM The Spitfire amplifier is designed to produce a near Gaussian output beam Beam uniformity is best checked by visually inspecting burn patterns made on Eastman Kodak s Linagraph paper commonly called burn paper The beam can be incident on either side of the burn paper giving differe
33. Ti Sapphire Regenerative Amplifer Systems 6 8 Chapter 7 Note The Spitfire Beam Path On occasion it might be necessary to make adjustments to the Spitfire internal optical components The beam path and its adjustment through the Spitfire are described below When describing the beam path left and right refer to the direction of travel moving along the beam from input to output A few of the more complex optical elements require some initial descrip tion Refer to Figure 7 1 below Faraday Isolator protects the seed laser components by absorbing any reflected power that is generated in the amplifier and absorbing pulses that are not selected for amplification There are no adjustments on this device Tall Stretcher End Mirror M is about 95 reflective so that only about 5 of the beam passes through it and is detected by the bandwidth detector BWD located behind the mirror The end mirror reflects the beam back onto the gold Mirror M Both M and M have vertical and hor izontal adjustments Bandwidth Detector BWD not shown in the drawings is a safety device that protects the system when there is not enough bandwidth in the seed pulse for it to be properly spread by the stretcher usually caused by a misaligned seed laser or one with poor mode locking See Chapter 4 Controls Indicators and Connections for more information about the BWD This device is pre set at the factory Vertic
34. WD is explained in Chapter 4 Controls Indicators and Connections along with instructions for operating the SDG II Specifications General Description The Spitfire amplifier systems are available in a number of configurations The tables below show the configurations covered in this manual Table 3 1 Spitfire Specifications by Model Amplifier Output Energy Pulse Pre Pulse Wavelength Model using these pump Width Contrast nm lasers Ratio Evolution Evolution X F 1K 750 uy 1mJ lt 130 fs 1000 1 750 900 F 5K 200 uJ 300 uJ lt 130 fs 500 1 750 900 P 1K 750 uJ 1 mJ lt 2 ps 1000 1 750 900 P 5K 200 uJ 300 uJ lt 2 ps 500 1 750 900 PM 1K 750 uJ 1 mJ 1 2 ps 1000 1 750 900 PM 5K 200 pJ 300uJ 1 2ps 500 1 750 900 USF 1K 500 uJ 750 uJ lt 90 fs 1000 1 750 900 USF 5K 150 uJ 225 uJ lt 90 fs 500 1 750 900 50 FS 1K 500 uJ 700 uJ lt 50 fs 1000 1 780 820 50 FS 5K 150 uJ 200 uJ lt 50 fs 500 1 780 820 l Due to our continuous product improvement program specifications may change with out notice Specifications listed on the purchase order supersede all other published specifications Designators IK and 5K refer to repetition rates of 1 kHz and 5 kHz respectively If optimum performance is required at more than one repetition rate an additional optic set is required Any system can be operated with the same energy per pulse at reduced repetition rates through the divide down electronics on the SDG II
35. Y as necessary Remember that the seed beam is currently blocked from entering the Spitfire 7 Adjust mirror M to center the cavity dumped beam through the aper tures of the removable iris 8 Relocate the removable iris to location X as shown in Figure C 4 9 Adjust mirror M to center the cavity dumped beam through the aper tures of the removable iris 10 Disable OUT 1 DELAY and OUT 2 DELAY on the SDG II 11 Close the pump beam shutter 12 Install the grating assembly or the compressor grating assembly for the Spitfire 50FS 13 Open the seed beam input shutter 14 Adjust the rotation of the grating assembly so that the pattern on the stretcher grating appears as shown in Figure C 1 15 Close the seed beam input shutter 16 Open the pump beam shutter 17 Enable OUT 1 DELAY and disable OUT 2 DELAY trigger pulses 18 Open the seed beam input shutter Verify the buildup time reduction it should be the same as when the seed beam optimization alignment procedure is performed 19 Enable the OUT 2 DELAY trigger on the SDG J and adjust the timing for cavity dumping the correct pulse 20 Verify that the cavity dumped output is centered on the iris 21 Using the IR viewer to look at the grating verify the pattern on the grating appears the same as in Figure C 2 If not go back and check the alignment through the iris 22 Remove the iris from the Spitfire then verify the output beam is not clipped Warning Failu
36. ain of stretched seed pulses and direct them into the amplifier The selected stretched pulses then pass multiple times through the regenerative amplifier Once the pulses are amplified the SDG I provides the timing control to direct the amplified pulses into the compressor The compressor shortens the amplified pulses close to their original duration using a second grating mirror combination The pulses are then directed out of the Spitfire Spitfire Ti Sapphire Regenerative Amplifer Systems Titanium Sapphire 1 4 The Spitfire amplifier gain media is a titanium doped sapphire Ti sap phire crystal Ti sapphire was selected because of its two very useful prop erties a it has a broad absorption band in the blue and green which allows it to be pumped by the frequency doubled output of a Nd YLF or a Nd YAG laser and b it is tunable over a broad emission band of wave lengths in the near infrared For a more detailed explanation of the theory of operation of the Spitfire refer to Chapter 3 General Description Chapter 2 Laser Safety Danger W Danger Laser Radiation The Spectra Physics Spitfire amplifier is classified as a Class IV High Power Laser whose beam is by definition a safety and fire hazard Take precautions to prevent accidental exposure to both direct and reflected beams Diffuse as well as specular beam reflections can cause severe eye or skin damage Because the output wavelength is typica
37. al separate high voltage supply The drivers themselves are located in the Spitfire below the regenerative amplifier cavity RS 232 control of the SDG II is described in Appendix A TRIGGER FREQUENCY INPUT DIVIDE control TRIGGER FREQUENCY kHz INPUT DIVIDE S Spectra Physics DG II SYNC ENABLE control and LED indicator BWD BWD PD1 PD2 RESET OUT 1 DELAY OUT 2DELAY SYNC OUT DELAY JWD OUT 1 MELAY ns OUT 2 HELAY ns SYNC OUT D LAY ns PD 1 RESET PD 2 displays x3 controls x3 CONTINUOUS ne wane ENABLE controls x3 SYNC ENABLE MOD MAN TRIG ENABLE ENABLE ENABLE i F LED indicators x3 connectors x3 Sync ERROR MODE control MAN TRIG LED indicator and LEDs control Figure 4 4 SDG II Front Panel 4 4 TRIGGER FREQUENCY display shows the output frequency in kHz set for the Spitfire INPUT DIVIDE control allows the output frequency of the SDG II to be reduced by integer divisors e g 2 3 etc This allows the output pulse rate of the Spitfire to be changed without changing the repetition rate of either the pump laser or the seed laser which might affect the stability of those lasers The largest division factor available corresponds to the reduction of the output to a 1 Hz repetition rate Thus the largest factor for a 1 kHz system is 1000 the largest factor for a 5 Khz system is 5000
38. al Retroreflectors x2 comprise a pair of flat mirrors at right angles that translate the beam up or down and reflects it back on a parallel path There is one of these assemblies in the stretcher and one in the com pressor each has vertical and horizontal adjustments Horizontal Retroreflector translates the beam sideways and reflects it back on a parallel path This compressor assembly has vertical and hori zontal adjustments In addition the horizontal retroreflector is mounted on a translational track that has a dc motor and motion controller Polarizer is an optical element that as used in the Spitfire is transparent to horizontally polarized light and reflects rejects vertically polarized light It is used to direct amplified pulses into the compressor Mounting screws provide vertical and lateral movement for alignment There are no other adjustments on this device 7 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Stretcher and Compressor Beam Paths Although the beam passes from the stretcher into the amplifier and then to the compressor the beam path in the stretcher and in the compressor are described together first since they share the same compartment and their treatment of the beam is similar Seed Pulses STRETCHER Stretcher Grating gt E VRR Amplified Compressor COMPRESSOR Output Grating REGENERATIVE AMPLIFIER Figure 7 1 Optical Component
39. and amplification stops In short after a single pass of a low energy pulse there is still a lot of gain left in the amplifier for more passes The Spitfire cavity is designed to first select and then optically confine an individual pulse from the train of mode locked seed pulses that have already been lengthened in duration in the stretcher Reducing the repeti tion rate from the megahertz mode locked pulse train to kilohertz rates enables the gain of the amplifier to be concentrated in fewer pulses thus producing more energy per pulse Immediately prior to passing the selected pulse through the Ti sapphire crystal for amplification the crystal is exited to population inversion by a high energy pulse from a separate pump laser The selected pulse is then passed through the crystal 20 or more times until the stimulated emission the pulse energy level is high enough to completely eliminate the popula tion inversion Having thus saturated the gain i e absorbed all the energy available the pulse is ejected into the compressor Typically an input pulse of only a few nanojoules of energy may be ampli fied to roughly a millijoule using a single Ti sapphire crystal and multiple passes through the regenerative amplifier can result in an energy amplifica tion greater than 10 at the output of the compressor When the compressor restores the short duration of the pulse the amplified energy results in cor respondingly amplified peak power
40. are Laser dispositivo de segu bare laserstraling locked en Cas D Ouverture strahlung wenn ge ff ridad exist radiacion Vermijd blootstelling Label et lorsque la securit net und laser visible y invisi van oog of huid ann 4 est neutralis e expo sition dangereuse de oeil ou de la peau au rayonnement direct ou diffus Laser de Classe 4 Sicherheitsverrie gelung Uberbruckt Bestrahlung von Augen oder Haut durch direkt oder Streustrahlung ver meiden Laser Klasse 4 ble evite que los ojos o la piel queden expuestos tanto a la radiacion directa como a la dispersa Producto laser clase 4 direkte straling of ter ugkaatsingen daar van Klas 4 laser produkt 2 6 Laser Safety CE Declaration of Conformity Low Emissions We Spectra Physics Inc Industrial and Scientific Lasers 1330 Terra Bella Avenue P O Box 7013 Mountain View CA 94039 7013 United States of America declare under sole responsibility that the Spitfire Multi Kilohertz Ti Sapphire Regenerative Amplifier System with SDG II Controller Manufactured after December 31 1996 meets the intent of Directive 89 336 EEC for Electromagnetic Compati bility Compliance was demonstrated Class A to the following specifications as listed in the official Journal of the European Communities EN 50081 2 1993 Emissions EN55011 Class A Radiated EN55011 Class A Conducted EN 50082 1 1992 Immunity IEC 801 2 Electrostatic Discharge IEC 801 3 R
41. ation Matrix eee teens 1 2 Table 1 2 Spitfire Optics Sets neee eee 1 2 Table 2 1 Label Translations eee 2 6 Table 3 1 Spitfire Specifications by Model 0 00 teen eens 3 11 Table 3 2 Spitfire Specifications Common to All Models 0 00 eee eens 3 11 Table 5 1 Pump Laser Specifications neee eee ee 5 2 Table 5 2 Seed Laser Specifications nnee 5 2 Table A 1 Quick Command Reference Guide enen enen eene A 2 xi Spitfire Ti Sapphire Regenerative Amplifer Systems xii Danger Laser Radiation Danger A Danger Warning Warning ESD A Caution Note Don t Touch Eyewear Required W W U W Y E A Warning Conventions The following warnings are used throughout this manual to draw your attention to situations or procedures that require extra attention They warn of hazards to your health damage to equipment sensitive procedures and exceptional circumstances All messages are set apart by a thin line above and below the text as shown here Laser radiation is present Condition or action may present a hazard to personal safety Condition or action may present an electrical hazard to personal safety Condition or action may cause damage to equipment Action may cause electrostatic discharge and cause damage to equip ment Condition or action may cause poor performance or error Text describes exceptional circumstances or makes a special refer ence
42. ble outputs on the front panel Spitfire Ti Sapphire Regenerative Amplifer Systems Warning W Motion Controller 4 8 INTERLOCK ENABLE switch enables or disables the 5VDC connector When the switch is up the connector is functional and the center pin of the BNC is grounded When the switch is down the connector is disabled 5VDC connector input accepts an input signal from a safety interlock switch provided by the user for example a switch that senses when a sim ple closed circuit has opened If this connector is enabled and the safety interlock switch opens OUT 1 DELAY and OUT 2 DELAY will be disabled The use of the 5VDC connector as a safety switch will not disable the pump or seed lasers These lasers have their own safety interlocks Please refer to their user s manuals If purchased from Spectra Physics these manuals are included with your system The Motion Controller provides translation control of the horizontal ret roreflector assembly in the compressor Moving this mount changes the length of the beam path in the compressor and provides the fine adjustment needed to compensate for small changes in the dispersion that take place in the amplifier cavity The Motion Controller connects to the 12 mm 2 pin connector on the Spit fire yeLOCin Newport Motion Controller Model 861 Figure 4 7 Motion Controller model may vary VELOCITY control sets
43. bright and constant display c Compensate for any adjustment of M1 with the opposite adjust ment of the tall mirror M so that the fourth pass of the beam in the stretcher is picked off by M3 Refer to the instructions in Chapter 6 for aligning the seed beam into the regenerative amplifier 10 Use the IR viewer to check the pattern on the compressor grating If necessary translate the compressor stage to obtain the correct pattern 11 The Spitfire should now be ready for femtosecond operation Converting the Spitfire F to PicoMask Operation A Spitfire F or a Spitfire USF may be converted to a Spitfire PM system if the system has been configured and tested at the factory for this option This procedure is very similar to the inverse procedure that is converting a Spitfire PM system to one of the femtosecond amplifiers Refer as needed to the figures used in the inverse procedure described in the previous section 1 Block the seed and pump beams or close the shutter on these lasers 2 Using the 16 in hex driver place the mask assembly on the mount in front of gold mirror M in the stretcher see Figure B 3 3 Remove the femtosecond grating assembly from the rotation stage by removing the two grating mounting screws they are either 14 20 or M3 screws see Figure B 4 Store the PicoMask grating assembly carefully Often the assembly can be stored in the stretcher compart ment by bolting it to the base plate next to the
44. ching inter lock read sta bwd none Reads the state of the BWD pho todiodes set rf 0 1 Enables 1 or disables 0 the RF sync read rf none Returns the state of the RF sync set mode 0 1 Sets the trigger mode to continu ous 0 or single shot 1 read mode none Returns the state of the trigger mode man trig none Manually triggers the SDG II when in single shot mode A 2 RS 232 Interface Full Command Description Note status Returns the status of the SDG I as a comma delimited list of eleven param eters whose values are shown in the following table Parameter of Characters Possible Values Output 1 state 1 O Off or 1 On Output 2 state 1 O Off or 1 On Sync Out state 1 O Off or 1 On Output 1 Delay 6 0000 0 ns to 1275 0 ns Output 2 Delay 6 0000 0 ns to 1275 0 ns Sync Out Delay 6 0000 0 ns to 1275 0 ns Trigger divisor 4 0001 or 0010 BWD switch state 1 O Off or 1 On BWD photodiode amp 3 000 to 111 Ext Interlock state see below under read sta bwd Mode 1 0 continuous or 1 single shot RF Sync state 1 0 Off or 1 On For the following four commands channel N 1 selects OUT 1 DELAY channel N 2 selects OUT 2 DELAY and channel N 3 selects SYNC OUT DELAY set cN Sets the output of channel N to be enabled 1 or disabled 0 read cN Returns the output state of channel N as enabled 1 or disabled 0 set del cN Sets the delay of channel N in nanose
45. ciple of Chirped Pulse Amplification Pulse Stretching and Compression A light pulse incident on a diffraction grating experiences dispersion that is its component wavelengths are spatially separated and so too are its fre quency components The dispersed spectrum can be directed through a combination of optics usually the same diffraction grating can be used to send the different frequencies in slightly different directions Longer or redder wavelengths can be made to travel over a longer path than the shorter or bluer wavelengths components of the beam or vice versa The result is to lengthen the duration of the pulse which reduces its peak power it is the same energy under the curve only spread out more now A prism which is a simpler optic than a diffraction grating can also be used for these purposes However because the pulse passes through a prism negative GVD is introduced by the glass or quartz of the prism body blue frequencies are delayed relative to the red frequencies each time the pulse passes through the prism Therefore gratings are the better choice for CPA because they simplify the process of compensating for dispersion caused by other components in the optical path The grating and the routing mirrors can be chosen so that in the stretcher the bluer frequency components of the spectrum travel further than the red der components causing the redder frequency components to exit the stretcher first In the
46. ckels cell acting as a 4 waveplate It is rotated 45 going in and 45 reflecting back from CM and becomes vertically polarized It is reflected out of the cavity by the horizontal polarizer The vertically polarized amplified pulse is reflected by the polarizer 15 to mirror Ms 16 To protect the compressor optics the beam is expanded by a telescope 17 comprising negative and positive lenses OL and OL to reduce pulse power density The expanded beam is directed into the compressor by the polarization rotating periscope PS 18 which changes the vertically polarized light from the amplifier to horizontally polarized light M6 see Figure 7 1 directs the beam into the compressor chamber 7 9 Spitfire Ti Sapphire Regenerative Amplifer Systems 7 10 The Pump Beam Path PM2 PL3 ed CMa i a Sia 7 TiS pphire Rod Telescope i Eee 0 Bi 2 vs 1 an did 0 Y Regenerative Amplifier Cavity ae 527 nm PL PLa PM p Pump Figure 7 8 Pump Beam Path The pump beam path is controlled as follows A telescope comprising negative lens PL and positive lens PL enlarge the pulsed beam from the pump laser The beam is enlarged so that it can be better focused into the Ti sapphire rod The lens mounts have vertical and horizontal adjustments Pump mirror PM directs the enlarged beam from the telescope to PM PM and PM are also used to set the height of the pump beam so that it is cen tered on pump lens PL Pump
47. compressor the spatially spread beam is flipped so that the redder component have to take the long path thereby allowing the bluer frequencies to catch up This recompresses the pulse Figure 3 4 shows a simplified pulse stretcher A short pulse is spectrally spread and then by making one end of the spread pulse travel farther than the other end the pulse is temporally broadened The same optical compo nents act as a compressor when the leading component of a temporally stretched pulse is forced to take the longer path thereby allowing the trail General Description ing component to catch up In the pulse stretcher shown below the bluer components are forced to take the longer path Creating Negative GVD redder shorter path EES Diffraction Grating 2 lt gt bluer longer path lt lt gt wavelength spatial spreading occurs with red leading the blue because red has a shorter distance to go pulse wavelengths are spread out here Diffraction Grating 1 gt bluer redder Input Pulse Stretched Output Pulse Figure 3 4 Principle of pulse stretching using negative GVD The Spitfire Pulse Stretcher and Compressor Note The Spitfire pulse stretcher and compressor make use of some simplifying modifications Instead of using two gratings for the stretcher a simple but elegant retroreflector mirror assembly directs the beam back onto a single grating in the stretcher This avoids the need to
48. conds ns The minimum increment for the SDG II is 0 25 ns The allowed values for the last digit after the decimal are 0 2 5 and 7 which corresponds to 0 00 0 25 0 50 and 0 75 ns respectively Last digits other than 0 2 5 or 7 are rounded down to the nearest allowed value read del cN Returns the delay setting for channel N The allowed values for the last digit after the decimal are 0 2 5 and 7 which corresponds to 0 00 0 25 0 50 and 0 75 ns respectively Spitfire Ti Sapphire Regenerative Amplifer Systems set rate Sets the divisor by which the input trigger frequency rep rate is divided in order to produce the desired output trigger frequency Allowed values are 0001 0002 0005 and 0010 For example if the input trigger rep rate is 1 000 kHz a rate of 0005 will set the output frequency to 0 200 kHz read rate Returns the input output frequency divisor set by the set rate command read bwd Returns the state O off 1 0n of the BWD mechanical switch on the back of the SDG II reset bwd Resets the BWD latching interlock If the BWD switch is on and both BWD photodiodes PD and PD are illuminated reset bwd will clear the BWD latching interlock If the BWD switch is off reset bwd will clear the BWD latching interlock regardless of the state of the BWD photodiodes read sta bwd Returns a string of three binary values The first two values are the states of the BWD photodiodes PD
49. cs including the pulse stretcher and compressor are optimized for the range of wavelength pulse width and repetition rate used This manual contains information on the optics sets and the stretcher and compressor configurations available for this system Please note that the Spitfire performance specifications can be met only if the mode locked Ti sapphire laser is operating within the specifications and requirements outlined in this manual The amplifier is designed specifically for the Spectra Physics Tsunami or Mai Tai lasers The Introduction contains a brief description of the Spitfire head assem bly and the SDG H controller Following that section is an important chapter on laser safety The Spitfire is a Class IV laser and as such emits laser radiation which can perma nently damage eyes and skin This section contains information about these hazards and offers suggestions on how to safeguard against them General Description contains an introductory section on laser theory pulse stretching laser amplification and pulse compression Specifications for the various Spitfire systems are included at the end of this chapter The next chapter is an overview of the external controls and external adjustments of the system Please familiarize yourself with this material before operating the amplifier Spitfire Ti Sapphire Regenerative Amplifer Systems The following chapter describes the preparation needed to install the S
50. ct pump beam alignment Refer to Appendix C for pump beam alignment procedures Damage to optical components Check for optical damage contact your Spectra Physics representative if present Compressor vertical retro reflector and or Contact your Spectra Physics representative horizontal retro reflector are incorrectly aligned in the horizontal axis Symptom Optical damage in the amplifier cavity Possible Cause Corrective Action Seed laser not well modelocked CW Contact your Spectra Physics representative breakthrough Partial restriction of the stretched spec Contact your Spectra Physics representative trum Failure to remove alignment tools from Contact your Spectra Physics representative optical path after checking stretcher or compressor alignment Incorrect alignment of amplifier cavity Contact your Spectra Physics representative Spitfire Ti Sapphire Regenerative Amplifer Systems Customer Service Warranty 8 6 At Spectra Physics we take great pride in the reliability of our products Considerable emphasis has been placed on controlled manufacturing meth ods and quality control throughout the manufacturing process Neverthe less even the finest precision instruments will need occasional service We feel our instruments have excellent service records compared to competi tive products and we hope to demonstrate in the long run that we provide excellent service to our customers in two ways first by p
51. d eee eee eee ee xiii Standard Units cis issi ode aa dale XV AppreviatlOns cui waa Oke aten ee es ek A eee eee w xvii Unpacking and Inspection oooooooccccccoc ee xix Unpacking Your SYSTEM zevental el EEE DEN WE REPORTED xix System Components ssc da seed ee ate eke ae ede Bn linen en eea xix ACCESSO Kit Sneed eee een oi bead A Obee eend Bad Ene be ele nare feed xix Chapter 1 Introduction S fiend ce tier ces ervarenen nek teense Owes 1 1 The Spitfire System neee eee 1 1 Configuration Ss aiea ntt laeten Hele dan LA a BS 1 2 Custom Spitfire Systems eee eee eeen 1 3 The Spitfire Amplifier ae 1 3 Titanium Sapphire enen enen 1 4 Chapter 2 Laser Safety nan sas eren in aa A harde ew ad a 2 1 Precautions For The Safe Operation Of Class IV High Power Lasers oenen 2 1 Safety DOVICOS gt van nieren a Herta be a a tet A be ead Nb ela BE 2 2 RUSOS rs etat ne er erde tand ited Seed is ander he betta A ibid 2 3 Maximum Emission Levels neee 2 3 CDRH i Compliance eaa 2 a da eender etn en ieee A BE 2 3 CDRH Requirements for Operating the Spitfire Using the Optional PC Control 2 3 CE CDRH Radiation Control Drawings onee eee eeen 2 4 GE CDRH Warning Labels ius ia Weta ed dons ee 2 5 Label Translations wrs aanwennen eren eea ten acetate ee ee 2 6 CE Declaration of Conformity Low Emissions 00000 cece eee eee eens 2 7 CE Declaration of Conformity Low Voltage oooooccocccnccnc a
52. d reflects the beam towards the horizontal ret roreflector HRR 6 7 with the redder wavelengths on the right and the bluer wavelengths on the left The grating mount has a rotational adjustment which it shares with the stretcher grating The horizontal HHR steps the beam over about two inches flips the ends of the spectrum and returns the beam to the lower left side of the grating 8 The redder wavelengths now take the shorter path The beam is reflected by the grating and impinges on the VRR 9 where it is stepped upwards an inch and is sent back to the top left side of the grating 10 which begins to refocus the beam and reflects it to the horizontal retroreflector 11 12 The horizontal retroreflector flips the beam around again and sends it back to the grating 13 where the beam is compressed back close to its original duration The beam is reflected over Mg 14 and exits the Spitfire The Spitfire Beam Path Spitfire USF Stretcher and Compressor The layout of the Spitfire USF is identical to that of the Spitfire F The only difference is that the grating ruling density is reduced in the Spitfire USF to accommodate its shorter pulses and therefore broader spectral band width The gratings are also set at a different angle to the beam Spitfire P Stretcher and Compressor The narrower spectrum of picosecond pulses as compared to femtosecond pulses requires greater dispersive power from the gratings in order to ad
53. ds The maximum output energy of a solid state amplifier is normally limited by the optical damage threshold of the crystalline material used in the sys tem The Spitfire regenerative amplifier circumvents this limitation by using chirped pulse amplification This technique originally developed for radar systems first temporally stretches a pulse to reduce its peak power then amplifies it and finally recompresses the pulse to a width close to its original duration This results in greatly increased peak power while avoiding optical damage to the amplifier The Spitfire System The Spitfire system itself comprises two main components e the Spitfire amplifier head assembly and the e the Synchronization and Delay Generator SDG ID However a complete system requires a pump laser to energize the Spitfire amplifier and a seed laser to provide the original pulses Figure 1 1 shows a typical application a Spitfire PM pumping an optical parametric amplifier seeded by a Mai Tai laser system and pumped by an Evolution laser 20s 2oi 4oj Mai Tai Os Op Os Oj l Os Oj gt 40s gt A Evolution Spitfire PM OPA 800CP gt i gt OS lea gt Op A Figure 1 1 A typical layout showing the Spitfire pumping a Spectra Physics OPA 800CP 1 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Configurations The Spitfire system is available in a variety of model
54. e quately reduce the peak power of these pulses before they can be safely amplified Therefore the Spitfire P uses gratings with an increased ruling density compared to that used on the Spitfire F and set at a different angle to the beam In addition the stretcher and compressor incorporate additional folding mirrors to increase the length of the beam path and give the separated wavelengths adequate distance to separate and recombine spatially Figure 7 4 illustrates the stretcher and compressor beam path for picosecond oper ation Note For clarity the dispersion of the beam is not shown in the same detail in Figure 7 4 as in the other stretcher compressor figures Stretcher M2 HRR Fold VAR a e Mirror O j E ME gt M OT Pulse Compressor Grating Amplified Figure 7 4 Modifications for the Spitfire P Spitfire PM Stretcher and Compressor The picomask version of the Spitfire is identical to the Spitfire F except that it uses the same gratings as the picosecond amplifier and a special mask aperture is added to the stretcher cavity to reduce the bandwidth of the femtosecond seed pulses The Spitfire PM does not require the extra path length in the stretcher and compressor that is needed by the Spitfire P This mask and its position in the stretcher in front of M are shown in Appendix B Changing To and From PicoMask Operation which pro vides instructions for converting Spitfire F and Sp
55. e at 800 nm the corresponding bandwidth is more than 9 nm Therefore a device that can delay certain frequencies or wavelengths relative to others can stretch a short pulse so that it lasts a longer time Likewise such a device should also be able to compress a long pulse into a shorter one by reversing the procedure The phenomenon of delaying or advancing some wavelengths relative to others is called Group Velocity Dispersion GVD or less formally chirp A pulse is said to have positive GVD or to be positively chirped when the shorter bluer wavelengths lead the longer redder wavelengths Con versely if the bluer light is delayed more than the redder light it has nega tive GVD or chirp For CPA a combination of dispersive optics are used to form a pulse stretcher where low energy short duration pulses can be lengthened by as much as 10 Then the energy in these pulses is increased by passing them Spitfire Ti Sapphire Regenerative Amplifer Systems through the Ti sapphire regenerative amplifier Finally a set of dispersive optics similar to those used in the stretcher are used to form a pulse com pressor to recompress the pulses to their specified duration Figure 3 3 illustrates this process Stretcher Amplifier A A de Low Power Reduced Power Amplified High Peak Power Short Pulse Stretched Pulse Stretched Pulse Compressed Pulse Pulses not to scale Figure 3 3 The Prin
56. e duration to close to its original length The retroreflector in the compressor is mounted on a track for easy transla tion in the direction along the beam path This fine adjustment is used to compensate for small routine changes in dispersion that take place in the amplifier cavity Translation control is provided by a motion controller and de motor The design details of the gratings and their optical configuration in a CPA system depend upon among other factors the duration of the seed pulses and output pulses Longer duration pulses have a correspondingly narrower spectrum of wavelengths and so require a higher density of rulings for the diffraction gratings to achieve an adequate degree of dispersion and stretch ing Each Spitfire model has its own stretcher compressor design The Spitfire F P PM and USF each use gratings that are designed for their specific pulse lengths and from the nature of the grating diffraction this means they each have their back to back gratings set at different angles to the beam path There are some other individual differences but overall these stretcher compressor designs are similar The Spitfire 50FS differs from the other models in the layout of its stretcher and compressor The Spitfire PM includes a masking element to change the bandwidth of the seed pulses The designs of the stretcher compressor combinations for both of these models is discussed in further detail below The Spitfire 50FS C
57. e e Spitfire Ti Sapphire Regenerative Amplifier Systems Spitfire F Spitfire USF Spitfire SOFS Spitfire P Spitfire PM User s Manual S Spectra Physics 1335 Terra Bella Avenue Mountain View CA 94043 Part Number 0000 255A Rev A August 2004 Preface This manual contains information you need to safely operate and maintain your Spectra Physics Spitfire Ti sapphire amplifier system The Spitfire is available in a wide variety of models this manual covers the Spitfire F P PM USF and 50FS versions Other versions of the Spitfire such as the Spitfire HP are described in their own manuals The Spitfire systems amplify short duration optical pulses emitted by mode locked Ti sapphire lasers such as those produced by the Spectra Physics Tsunami or Mai Tai The Spitfire can amplify either picosecond pulses or femtosecond pulses at near infrared and red wavelengths Two basic repetition rates are available 1 kHz and 5 kHz and the system can be adjusted for lower pulse repetition rates The system comprises two units the Spitfire head assembly and its control unit the Synchronous Delay Generator or SDG II The SDG II is a table top unit that is provided with all systems The Spitfire amplifier head itself contains three assemblies a pulse stretcher a Ti sapphire regenerative amplifier and a pulse compressor The Spitfire stretcher and compressor designs are based on the pulse width of the input and output pulses The opti
58. ed triggered and operating e the intracavity apertures are not blocking the beam e a power meter capable of measuring between 10 mW and 20 W of average power from 500 nm to 900 nm e a fast CRT analog oscilloscope capable of 300 MHz or better e a fast photodiode with a 2 ns rise time or better IR viewer and IR card e a small low divergence HeNe laser for alignment e an autocorrelator e g Spectra Physics Model SSA e scales rulers to measure up to 10 in and 25 cm e three gimbal mounts with 4 6 in adjustable height e three silver mirrors for the above mounts e alignment pins e 1 Phillips screwdriver e a standard English hex driver set e a standard English hex ball driver set e a metric hex driver set e white business card e trim pot screwdriver e _ lens tissue e gel linear polarizing film Alignment Stretcher Alignment Check If you cannot see the beam in the amplifier it will be necessary to check the alignment through the stretcher as follows 1 Use an IR viewer to look at the beam pattern on the stretcher grating It should look like that in Figure C 1 Figure C 1 Radiation Patterns on Stretcher Gratings 2 4 If the beam pattern does not look like Figure C 1 then it is likely that the wavelength of the seed laser has changed In order to return to the previous operating conditions adjust the seed laser wavelength until the pattern is symmetrical on the grating as shown here
59. els cell HSD 2 connector BNC connects to the OUT 2 DELAY connector on the front of the SDG II for triggering the output Pockels cell BWD OUT connects to the 4 pin BWD connector on the back of the SDG II DC MOTOR input connector connects to the motor controller provided with the system that drives the micrometer motor which sets the length of the compressor Refer to Motion Controller below Cooling water connections provide cooling water for the amplifier rod Water is shared serially downstream from the seed laser Mai Tai or Tsu nami Either connector may be used as the IN or OUT connection for the water flow Controls Indicators and Connections Output End Panel Alignment Laser Amplified Pulse Input Port Output Port DA PHOTODIODE Photodiode Connector Figure 4 3 Spitfire Panel Output End Photodiode connector provides connection for the high speed photo diode that samples the intracavity signal of the Spitfire The signal can be monitored using a high speed oscilloscope or spectrometer Amplified pulse output port is the exit port for the amplified pulse Alignment laser input port allows the beam of an alignment HeNe laser to be injected into the amplifier optical train without removing the output end panel To use this port remove the photodiode module inside the amplifier The photodiode detector module resides directly behind the end mir
60. er beam is misaligned SDG II controls are disabled Problem with high speed driver s Check the two BWD LEDs on the SDG II If both LEDs are on reset the interlock button of the BWD If one or both LEDs are off verify the seed laser is mode locked and that the wavelength is centered as specified Reset the BWD interlock button after restoring seed laser operation Refer to seed laser user s manual for further instructions Refer to the pump laser user s manual for further instructions Optimize the seed laser alignment Verify the unit is turned on and that the settings for OUT 1 DELAY and OUT 2 DELAY SYNC ENABLE and MODE con trol for CONTINUOUS or SINGLE SHOT operation are prop erly set Contact your Spectra Physics representative Symptom Regenerative Amplifier power is below specification Possible Cause Corrective Action Optics are dusty Optics are damaged Seed laser beam is misaligned Pump laser is power low Pump laser beam is misaligned Regenerative Amplifier is misaligned Timing of Pockels cells is incorrect Use dry nitrogen to blow dust from the optics with particular attention to the pump path and regenerative amplifier optics Check the optical components in the regenerative amplifier If an optic has been damaged contact your Spectra Physics repre sentative to arrange to have the optic changed It may be pos sible to use an undamaged portion of the optic face and realign the regene
61. et Output Wavelength Range Optics Set 1 750 nm 840 nm Optics Set 2 840 nm 870 nm Optics Set 3 870 nm 900 nm The wavelength range of interest was specified when your Spitfire system was ordered But there are separate optics sets depending on whether the system will be run at 1 kHz or 5 kHz Introduction Custom Spitfire Systems Custom versions of the Spitfire are available that produce pulses at different wavelengths higher power pulses or pulses at repetition rates other than those listed in Table 1 1 Again contact your Spectra Physics representa tive for more information The Spitfire Amplifier The Spitfire amplifier contains the optics and opto mechanical devices for stretching selecting amplifying and compressing pulses from a seed laser such as a Spectra Physics Mai Tai or Tsunami The Spitfire amplifier comprises the following three assemblies e the optical pulse stretcher e the regenerative amplifier e the optical pulse compressor These assemblies are each carefully optimized for the chosen wavelength range the repetition rate of the amplified output and the duration of the amplified pulses Spitfire Regenerative Amplifer Amplifier Figure 1 2 Block Diagram for the Spitfire F P PM USF and 50FS Incoming seed pulses are stretched using a multi pass grating and mirror combination The SDG II provides the synchronization and control needed to select and capture individual pulses from the tr
62. f switch HIGH VOLTAGE HV1 HV2 connectors provide 1 6 kVdc output for 1 kHz systems via high voltage cables to the HSD1 and HSD2 connections on the Spitfire for the two Pockels cells Voltage for 5 kHz systems is supplied by an auxiliary power supply and the HV1 and HV2 connectors on the SDG II are not used on these sys tems Cap these connectors if a 5 kHz system is used BWD ON switch and 4 pin connector see Bandwidth Detector on page 4 6 RS 232 connector provides attachment to a serial connection on a com puter for controlling the SDG H remotely Refer to Appendix A for infor mation on the computer control language used with this system RF SYNC connector connects via a high speed cable to the modelock synchronization output on the seed laser If a Mai Tai or Tsunami is used connect to the 40 MHz output connector refer to the appropriate user s manual Jitter is specified at lt 250 ps input impedance is 1 MQ internally switchable TRIGGER IN connector accepts TTL compatible 0 50 kHz input from the Q switch synchronization output of the pump laser If a Spectra Physics Evolution pump laser is used connect to the SYNC OUT connector on the front panel of the power supply Input impedance is 50 Q internally swit chable TRIGGER OUT connector provides a 200 ns fixed output trigger signal The input pulse trigger to the SDG I produces this TRIGGER OUT signal and applies it to the three adjusta
63. ferent wavelength range is required contact your Spectra Physics representative If converting the Spitfire from femtosecond Spitfire F or Spitfire USF to picosecond operation Spitfire PM or the reverse refer to the relevant pro cedures in Appendix B It is not necessary to realign the amplifier cavity for these procedures Spitfire Ti Sapphire Regenerative Amplifer Systems Try This First Tools Required To understand these procedures it is important to realize the Spitfire can operate as a laser as well as an amplifier that is it can be configured to produce its own pulsed output when energized by the pump laser even when the input from the seed laser is blocked Begin these procedures with the pump laser and the seed laser on and warmed up with both beams blocked shuttered from entering the Spitfire If your system is lasing but performance has degraded slight adjustments might only be required in pump beam power or to the pump beam routing mirror PM refer to Figure C 3 to optimize output rather than performing a complete realignment Before beginning any realignment verify the following e there is sufficient pump power e the pump beam has not been misaligned e the SDG II OUT 2 DELAY is sufficiently beyond OUT 1 DELAY see Basic Performance Optimization on page 6 3 e the 5VDC ENABLE switch on the SDG II back panel is in the disabled or down position e the Pockels cells are properly connect
64. g the internal apertures Symptom Output power or output spectrum is unstable Possible Cause Corrective Action Power variation in the pump laser Power variation in the regenerative ampli fier Spectrum modulated Incorrect adjustment of the 14 wave voltage to one or both Pockels cells Excessive jitter on Spitfire output pulse Unstable seed laser performance Incorrect timing of the INPUT POCKELS CELL Defective SDG II or Failure of high speed driver s See troubleshooting guide in the pump laser User s Manual Check the settings for OUT 1 DELAY and OUT 2 DELAY Check chiller flow and water level Contact your Spectra Physics representative See troubleshooting guide in the seed laser user s manual Check the settings for OUT 1 DELAY Contact your Spectra Physics representative Maintenance and Troubleshooting Symptom Poor contrast ratio Possible Cause Corrective Action Pre pulse Incorrect alignment of the output Contact your Spectra Physics representative Pockels cell Incorrect alignment of the 14 wave Contact your Spectra Physics representative plate for the input Pockels cell Post pulse Incorrect alignment of the Input Contact your Spectra Physics representative Pockels cell Incorrect adjustment of the wave Contact your Spectra Physics representative voltage for Input Pockels cell Symptom Poor output beam quality Possible Cause Corrective Action Incorre
65. ge of the Al aluminium ions A boule of material is then grown from this melt The Ti ion is responsible for the lasing action in Ti sapphire The elec tronic ground state of the Ti ion is split into a pair of vibrationally broad ened levels as shown in Figure 3 1 20 Relaxation E Infrared F Fluorescence S o Blue green gt Absorption gt lt ui 2 Tog 0 Figure 3 1 Energy Level Structure of Ti Sapphire 3 1 Spitfire Ti Sapphire Regenerative Amplifer Systems 3 2 Absorption transitions occur over a broad range of wavelengths from 400 to 600 nm only one of which is shown in Figure 3 1 Fluorescence transi tions occur from the lower vibrational levels of the excited state to the upper vibrational levels of the ground state The resulting emission and absorption spectra are shown in Figure 3 2 Although the fluorescence band extends from wavelengths as short as 600 nm to wavelengths greater than 1000 nm lasing action is only possible at wavelengths longer than 670 nm because the long wavelength side of the absorption band overlaps the short wavelength end of the fluorescence spectrum Additionally the tuning range may be reduced by variations in mirror coatings tuning element losses pump power and pump mode qual ity Nevertheless Ti sapphire possesses the broadest continuous wavelength tuning range of any commercially available laser As discussed in the fol lowing sections this broad tuning ra
66. he more obvious connections are not shown ac power for the SDG II for example Also not shown are the power water and control connections for the pump laser and seed laser Refer to the Mai Tai or Tsunami seed laser and the Evolution pump laser user s manuals for this information Spitfire Regenerative Amplifier As shown for 1 kHz systems The Spitfire connects to an auxiliary power supply in 5 kHz systems gt HSD 1 TRIG1 gt HSD 2 TRIG1 Safety Interlock BWD x gt BWD gt HSD 2 Evolution Power Supply SYNC OUT TRIGGER IN Motlon Controller gt gt DC MOTOR Mai Tai or Tsunami Seed Laser 40 mHz RF SYNC OUT 1 DELAY OUT 2 DELAY Figure 5 1 Spitfire Interconnect Diagram 1 kHz 5 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Spitfire Regenerative Amplifier High Voltage Power Supply gt BWD gt HSD 1 gt HSD 1 TRIG1 gt HSD 2 TRIG1 gt HSD 2 Safety Interlock Y BWD Evolution Power Supply SYNC OUT TRIGGER IN Motlon Controller gt gt DC MOTOR Mai Tai or Tsunami Seed Laser 40 mHz RF SYNC OUT 1 DELAY OUT 2 DELAY Figure 5 2 Spitfire Interconnect Diagram 5 kHz 5 6 Chiller Preparing for Installation The Spitfire Ti sapphire amplifier rod must be cooled to avoid damage The cooling water provided by the
67. hieve near transform limited output pulses it is necessary to compensate for the pulse spreading caused by positive GVD and SPM This is accomplished by using a compressor grating with a higher ruling density than the stretcher grating Such a design no longer permits the same ruling density to be used for both the stretcher and the compressor grating as in the other Spitfire models Furthermore using a different ruling density for each gratings requires each grating to be presented to the beam at a different angle which then varies as the unit is tuned for wavelength Therefore the Spitfire 50FS uses separate grating mounts rather than the shared single adjustment mount found in the other Spitfire models However the same four pass design can be used for the beam paths in the stretcher and in the compressor in order to obtain adequate spatial separa tion of the pulse s wavelength components The beam in the Spitfire SOFS follows the same sequence from optic to optic as outlined earlier for the Spitfire F The Ti Sapphire Regenerative Amplifier The Spitfire Beam Path Polarizer 1A2 Rod Pockels Cell E Input A1 waveplate Pockels Cell A from Stretcher DD A 1 vertically polarized light Figure 7 7 Regenerative Amplifier Beam Path Spitfire models all make use of a regenerative amplifier in a Z shaped 29 eeh folded cavity Refer to Figure 7 6 for component names
68. ially oper ated as an optically pumped Q switched laser In this configuration the Spitfire is capable of producing gt 1 5 W of average power at a wave length near 800 nm Use appropriate caution Block the seed beam Open the pump laser shutter Disable OUT 2 DELAY The regenerative amplifier will begin to operate as a laser Allow it to stabilize for about 5 minutes Monitor the intracavity pulse using the output of the photodiode behind CM Use a fast oscilloscope with a micro channel plate screen or a digitizing oscilloscope with a sampling rate greater than 2 GHz Trigger the oscilloscope externally with the SDG IJ SYNC OUT DELAY Set the time base to 100 or 200 ns div Use a 50 Q input impedance for the photodiode The pulse should appear as shown in Figure 6 3 Figure 6 3 Appearance of Q switched Pulse 5 Unblock the seed beam The energy of the seed laser pulses will now overcome the energy of the spontaneous emission in the Ti sapphire rod in the regenerative amplifier so that it now amplifies the seed pulses The intracavity radiation should now look like that shown in Figure 6 4 6 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Figure 6 4 Intracavity Pulse Train 6 Reduce the pulse build up time to the minimum possible While moni toring the pulse train make small iterative adjustments to turning mir rors Mz and M which direct the seed pulse into the resonator
69. igure B 5 Unblock or unshutter the seed laser to allow the seed beam to enter the stretcher Using the IR viewer rotate the grating stage until the correct femtosec ond pattern on the stretcher grating is observed Spitfire Ti Sapphire Regenerative Amplifer Systems Grating Mounting Screws Stage Screw sic POSITION a Seed Beam _ Stage Screw amp e Hidden a z p Figure B 4 Rotation Stage Picosecond Configuration Grating Mounting Screws Stage Screw rico rooien o o sae e e e Seed Beam be p 2 __ Stage Screw Hidden Figure B 5 Rotation Stage Femtosecond Configuration 9 Next adjust the BWD photodetectors for the new pulse bandwidth in the stretcher while observing the signals for PD and PD on the SGD II a Loosen the 0 050 in setscrews on top of the BWD photodetector slide assembly behind the tall mirror M Figure B 6 For femto second operation move the photodiodes apart until the LEDs on the SGD II just flicker then slide them together slightly until they produce a bright and steady glow Changing to from PicoMask Operation Photodiode Adjustment Screws Figure B 6 Adjustment Screws for the BWD Photodiodes Note The design of the adjustment for the BWD photodiodes differs depend ing on the date of manufacture of the Spitfire b If either or both BWD LEDs are not brightly lit then slightly adjust gold mirror M up or down until both LEDs produce a
70. is warranty is limited to repairing replacing or giving credit for the purchase price of any equipment that proves defective during the warranty period provided prior authorization for such return has been given by an authorized representative of Spectra Physics Spectra Physics will provide at its expense all parts and labor and one way return shipping of the defective part or instrument if required In warranty repaired or replaced equipment is warranted only for the remaining portion of the orig inal warranty period applicable to the repaired or replaced equipment This warranty does not apply to any instrument or component not manufac tured by Spectra Physics When products manufactured by others are included in Spectra Physics equipment the original manufacturer s war ranty is extended to Spectra Physics customers When products manufactured by others are used in conjunction with Spectra Physics equipment this warranty is extended only to the equip ment manufactured by Spectra Physics Maintenance and Troubleshooting This warranty also does not apply to equipment or components that upon inspection by Spectra Physics discloses to be defective or unworkable due to abuse mishandling misuse alteration negligence improper installa tion unauthorized modification damage in transit or other causes beyond the control of Spectra Physics This warranty is in lieu of all other warranties expressed or implied and does not cover i
71. it builds up It should look like that shown in Figure 6 4 Block the seed beam into the Spitfire and observe the intracavity Q switched pulse Figure 6 3 as it builds up If the Q switched pulse is unstable in amplitude or time make slight adjustments to end mirrors CM and CM With the oscilloscope trig gered by the SYNC OUT DELAY on the SDG II the Q switched buildup time reduction should be approximately 100 150 ns Unblock the seed beam into the Spitfire The pulse train should look like that shown in Figure 6 4 Make small iterative adjustments to mirrors M and M to reduce the pulse buildup time as much as possi ble that is adjust it so that the pulse train shifts from right to left on the oscilloscope screen By alternatively blocking and unblocking the seed beam into the Spit fire the difference between the unseeded Q switched time and the seeded pulse train time can be measured This difference in buildup time should be approximately 50 80 ns Re enable OUT 2 DELAY on the SDG II Again the intracavity pulse train should look like that shown in Figure 6 5 If it does not adjust OUT 2 DELAY so that the highest amplitude pulses in the train remain Position the photodiode at the output port of the Spitfire to look at the ejected pulse Make slight adjustments to OUT 2 DELAY to eject the pulse that has the best stability Adjust OUT 1 DELAY slightly if there is evidence of a secondary pulse being ejected 6 7 Spitfire
72. itfire USF femtosecond models to and from picomask operation 7 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Spitfire 50FS Stretcher and Compressor Seed Input 4 PASS STRETCHER 4 PASS COMPRESSOR Redder wer A gt Amplified A Pulse Figure 7 5 Spitfire 50FS Stretcher and Compressor Beam Path Amplification of pulses of the shortest duration requires that extra attention be paid to correcting the dispersion that occurs within the amplifier cavity Each Fourier component frequency of a pulse experiences a slightly differ ent index of refraction as it propagates though a material causing a time delay between the different frequencies Group Velocity Dispersion GVD is defined as the variation in the time delay as a function of wavelength Typically GVD causes red frequencies to travel faster than blue frequen cies The effect is more pronounced for shorter pulses such as those ampli fied by the Spitfire 50FS In addition to GVD the pulse width is affected by the nonlinear index of Ti sapphire which results in self phase modulation SPM As the pulse propagates through the Ti sapphire material the leading edge is red shifted by an increasing index of refraction Conversely the trailing edge of the pulse is blue shifted More information about GVD SPM and dispersion compensation can be found in the Mai Tai or Tsunami user s manuals In order to ac
73. ive input Pockels cell again through the aperture and is reflected by CM 6 this time to the Ti sapphire rod Because it is now horizontally polarized it passes through the rod and picks up first pass gain 3 The pulse is reflected by CM 7 through the horizontal polarizer through aperture A and through the inactive output Pockels cell 4 The pulse reflects off CM 8 and passes back through the inactive out put Pockels cell through aperture A through the horizontal polarizer reflects off CM 9 and passes back through the Ti sapphire rod for second pass gain 5 The beam reflects from CM 10 passes through the inactive input Pockels cell and is again reflected back from CM 11 Having passed twice through 4 it is now vertically polarized and is reflected from the surface of the Ti sapphire rod and out of the amplifier cavity to M Once rejected the pulse passes back through the stretcher and is absorbed by the Faraday isolator The Spitfire Beam Path Case b Input Pockels cell is already on pulse is rejected 1 The incoming vertically polarized pulse reflects off CM 4 and passes through aperture A But this time as it passes through the now active input Pockels cell it is rotated 45 by the cell and another 45 as it passes through 4 becoming horizontally polarized After reflecting off CM 5 it is rotated another 45 by 4 and another 45 by the still active input Pockels cell and retur
74. k into a round beam However the bluer components are now well ahead of the red Because the beam hits high on the concave mirror it is reflected to the bottom of the grating and as it leaves the grating it is now low enough to be picked off by mirror M 17 It exits the stretcher and is routed into the regenerative amplifier M has vertical and horizontal adjust ments 7 3 Spitfire Ti Sapphire Regenerative Amplifer Systems The Spitfire F Compressor Compressed Amplified Pulse gt Stretched Amplified Pulse AMPLIFIER A en v SS Dl gt Figure 7 3 Spitfire F Compressor Beam Path The temporally stretched pulsed beam passes from the stretcher into the regenerative amplifier After 1t achieves its maximum level of amplifica tion the beam is then ejected out of the regenerative amplifier by the hori zontal polarizer see Figure 7 6 The mechanism for ejecting the beam from the amplifier is discussed in The Ti Sapphire Regenerative Ampli fier on page 7 7 1 Ms 1 directs the vertically polarized beam through the expanding telescope 2 comprising OL and OL to reduce the beam intensity in the compressor Polarizing periscope PS 3 rotates the beam to horizontal polariza tion and directs it to the compressor routing mirror Me 4 which then sends it onto the right side of the compressor grating 5 Mg has verti cal and horizontal adjustments The grating spreads an
75. ll Stretcher Mirror Ma seed beam 4 X amplified beam We 1 Se Ys gt notch 1 EN Gold Mirror ps Mask Stretcher Compressor M Grating Grating Figure B 2 Modifications to the Stretcher for PicoMask Operation B 2 Note a Warning W Changing to from PicoMask Operation Surface of Gold Mirror Mask Positioning Block Mask Mounting Screw Figure B 3 PicoMask Assembly Mounting 3 Remove the picosecond grating assembly from the rotation stage by removing the two grating mounting screws they are either 14 20 or M3 screws see Figure B 4 Store the grating assembly carefully Often the assembly can be stored in the stretcher compartment by bolt ing it to the base plate next to the wall by the Tall Stretcher Mirror The configuration of the mask mount differs depending on the date of manufacture of the Spitfire Take care that the Allen wrench or hex driver does not touch the surface of the grating which is close to the mounting screws Loosen the two 14 20 screws that secure the rotation stage and slide the stage forward to the femtosecond position as marked on the base plate of the amplifier assembly see Figure B 4 Tighten the two 14 20 screws to secure the rotation stage in the femto second position Place the Spitfire F or the Spitfire USF femtosecond grating assembly on the rotation stage and secure it using the two mounting screws that were removed in Step 3 see F
76. lly between 700 and 1000 nm from red to infrared the Spitfire output beam is often invisible and therefore especially dangerous This type of infrared radiation passes easily through the cornea of the eye and when focused on the retina can cause instantaneous and permanent damage Precautions For The Safe Operation Of Class IV High Power Lasers Wear protective eyewear at all times selection depends on the wave length and intensity of the radiation the conditions of use and the visual function required Protective eyewear is available from suppliers listed in the Laser Focus World Lasers and Optronics and Photonics Spectra buyer s guides Consult the ANSI and ACGIH standards listed at the end of this section for guidance Maintain a high ambient light level in the laser operation area so the eye s pupil remains constricted reducing the possibility of damage Avoid looking at the output beam even diffuse reflections are hazard ous Avoid blocking the output beam or its reflections with any part of the body Establish a controlled access area for laser operation Limit access to those trained in the principles of laser safety Enclose beam paths wherever possible Post prominent warning signs near the laser operating area Figure 2 1 Set up experiments so the laser beam is either above or below eye level Set up shields to prevent any unnecessary specular reflections or beams from escaping the laser operation area Se
77. ly basis nevertheless they are fundamental to proper operation of the system and so are considered routine For convenience Figure 6 2 shows the components used to align the seed beam into the Spitfire regenerative amplifier The details of the optical design of the Spitfire models are described in Chapter 7 Stability of the Seed Pulses The mode locked output of the seed laser must be optimized to ensure good stability of the amplifier Refer to the seed laser user s manual In par ticular it is important that the duration of the seed pulse be not too long because the stretcher may not sufficiently reduce the peak power to avoid damage to the Spitfire optics Use a scanning autocorrelator to monitor the seed pulse duration Seed Beam Alignment into the Regenerative Amplifier Seed Pulses STRETCHER Stretcher Grating Compressor COMPRESSOR Grating I CM4 w Output Pockels Cell A3 Rod Oo Jon 14 Input waveplate Pockels Cell REGENERATIVE AMPLIFIER Figure 6 2 Optical Path for Seed Beam Alignment Spitfire Ti Sapphire Regenerative Amplifer Systems Beam Uniformity Warning W Caution W The input beam is directed by SM through the Faraday Isolator Fl and the first two alignment apertures A and A It is then routed by seed mirrors SM and SM through the vertical retro reflector VRR and onto the stretcher diffraction grating SM SM and
78. ly be blown clean with dry nitro gen Attempting to clean these components will permanently damage them The optics in the Spitfire should be carefully cleaned with soft optical tis sue and reagent grade methanol or acetone as described below 1 Always wash your hands first 2 Wear finger cots whenever optics are handled 3 Hold one sheet of lens tissue over the optic to be cleaned 4 Using the eyedropper place a single drop of good quality methanol on top of the lens tissue m Drag the lens tissue across the optic only once D If a residue of solvent is left on the optic repeat the procedure using less solvent and a new lens tissue until no residue remains For hard to reach optics 1 Wear finger cots or gloves 2 Fold a piece of lens tissue repeatedly to form a pad of approximately 1 cm wide 3 Hold the pad with a pair of hemostats so about 3 mm of the folded edge protrudes from the hemostat blades Saturate the pad with methanol or acetone and shake dry Reach slightly on one edge of mirrors and wipe the surface of the mir rors toward the outside in one motion Use each pad only once Be very careful that the tip of the hemostats does not scratch the mirror Troubleshooting Symptom No Spitfire output Maintenance and Troubleshooting Possible Cause Corrective Action BWD interlock is open Seed laser is not functioning correctly Pump laser is not functioning correctly Seed las
79. maintaining proper pump beam mode in the rod The correct placement of PL should be marked on the base plate of the amplifier head assembly 10 Return the pump laser to Q switched operation and adjust it to the power level noted in Step 1 If the required pump power is not known set the pump power to 10 W Note g Danger Laser Radiation 11 Alignment The Spitfire should now operate as a laser If it does not scan the pump beam waist across the Ti sapphire crystal face until it is superposed onto the intracavity beam waist To do this position the pump beam rather high in the crystal and off to one side using PM Now slowly translate the pump beam across the crystal face to the opposite side Lower the beam position in the crystal 0 5 mm and slowly translate back across the crystal face Continue this scanning process until the amplifier resonator begins to lase The Ti sapphire crystal emits less fluorescence when the Spitfire begins to lase While scanning watch for this rather than for an output from the thin film polarizer which necessitates watching both the crystal for safety and the output for lasing 12 13 14 Once the amplifier has begun to lase position a power meter just before the second lens of the beam expanding telescope OL Adjust PM vertically and horizontally for a symmetrically shaped out put mode it should approach a single order mode This should also coincide with maximum
80. match or to precisely align two stretcher gratings The beam is also multi passed to achieve greater spectral spread at reduced complexity and cost The same design principal is used in the compressor but in reverse The result is only two gratings are used in the entire system instead of four sim plifying the alignment and maintenance of the system If the input to the Spitfire is tuned to a different wavelength the diffraction grating in the stretcher will cause the beam to move and the grating must be rotated to realign the stretcher Naturally the compressor grating must be rotated by exactly the same amount to ensure optimum pulse compres sion To make this adjustment simple the Spitfire stretcher and compressor grat ings are arranged back to back on the same mount so that only one adjust ment is necessary to accommodate a change in wavelength The gratings for the Spitfire 5 0FS model are mounted separately and therefore must be adjusted individually Refer to Chapter 7 for details Spitfire Ti Sapphire Regenerative Amplifer Systems The stretcher and compressor occupy a single chamber and are separated from the amplifier by an air baffle that minimizes air currents through the stretcher and compressor The compressor uses a horizontal retroreflector to flip the red and blue components so that the bluer wavelengths are now forced to take the longer path This allows the redder wavelengths to catch up and reduce the puls
81. mation Modelocked Seed Laser The Spitfire was designed with a Tsunami or Mai Tai mode locked Ti sap phire seed laser in mind These are exceptionally stable systems Spectra Physics is not responsible for problems caused when a laser other than one of these is used to seed the Spitfire laser The seed laser must meet the following specifications Table 5 2 Seed Laser Specifications Wavelength 750 950 nm Power gt 400 mW Beam Diameter at 1 e points lt 2 mm Stability lt 1 rms Pulse Length lt 85 fs Spitfire F Spitfire PM lt 60 fs Spitfire USF lt 30 fs Spitfire 50FS lt 1 3 ps Spitfire P Polarization Linear vertical Beam Divergence full angle lt 0 6 mrad Preparation Location and Layout Required Utilities Preparing for Installation Each user will probably have unique layout requirements based on the application and the requirements and layout of the experiment so when choosing a layout please consider the following e The Spitfire head covers an area of table space as follows 5 x 2 ft 1 9 x 0 75 m for the Spitfire 50 FS 4 x 2 ft 1 5 x 0 75 m for the Spitfire E P PM USF e Allow sufficient space around the assembly for water hoses high volt age connections etc e Select a location where the electrical utilities for all the laser systems are readily available Spectra Physics strongly recommends that the laser system be located in a laboratory environment 1 e a room that is free from d
82. ment and Training 2 10 Laser Safety Guide Laser Institute of America 13501 Ingenuity Drive Suite 128 Orlando FL 32826 Tel 407 380 1553 Tel 800 34 LASER Internet www laserinstitute org Laser Focus World Buyer s Guide Laser Focus World Penwell Publishing 98 Spit Brook Road Nashua NH 03062 Tel 603 891 0123 Internet http lfw pennet com home cfm Photonics Spectra Buyer s Guide Photonics Spectra Laurin Publications Berkshire Common PO Box 4949 Pittsfield MA 01202 4949 Tel 413 499 0514 Internet www photonics com directory bg XQ ASP QX index htm Chapter 3 Ti Sapphire General Description The Spitfire amplifier system contains all the components necessary to amplify low energy Ti sapphire laser pulses to energy levels as high as a millijoule The Spitfire amplifier comprises the optical stretcher the regen erative amplifier and the optical compressor The femtosecond or picosec ond seed pulses to be amplified are provided by a separate mode locked Ti sapphire laser system The Spitfire system also includes the Synchronization and Delay Generator the SDG I which provides the precise timing required to select pulses for amplification and to eject them from the amplifier The functions of both the amplifier and SDG II are described in this chapter Ti sapphire is a crystalline material produced by introducing Ti O3 into a melt of Al O3 where Ti titanium ions replace a small percenta
83. ncidental or consequential loss The above warranty is valid for units purchased and used in the United States only Products shipped outside the United States are subject to a war ranty surcharge Return of the Instrument for Repair Warning m Contact your nearest Spectra Physics field sales office service center or local distributor for shipping instructions or an on site service appointment You are responsible for one way shipment of the defective part or instru ment to Spectra Physics We encourage you to use the original packing boxes to secure instruments during shipment If shipping boxes have been lost or destroyed we recom mend that you order new ones We will return instruments only in Spectra Physics containers Always drain the cooling water from the laser head and chiller before shipping Water expands as it freezes and will damage the laser Even during warm spells or summer months freezing may occur at high alti tudes or in the cargo hold of aircraft Such damage is excluded from warranty coverage Spitfire Ti Sapphire Regenerative Amplifer Systems Service Centers Belgium Telephone 32 0800 1 12 57 France Telephone 33 0810 00 76 15 Germany and Export Countries Spectra Physics GmbH Guerickeweg 7 D 64291 Darmstadt Telephone 49 06151 708 0 Fax 49 06151 79102 Japan East Spectra Physics KK East Regional Office Daiwa Nakameguro Building 4 6 1 Nakameguro Meguro ku Tok
84. nded it is possible to use other seed or pump lasers as components in a Spitfire system In particular seed lasers other than the Mai Tai or Tsunami will likely require a pre collimation to avoid the introduction of spatial chirp in the stretcher 5 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Pump Laser The Spitfire is designed for optimum performance when pumped by a Spectra Physics Evolution laser a frequency doubled Nd YLF laser Care has been taken to match the Spitfire optics to this pump laser especially with regard to wavelength beam diameter divergence and the ability to focus the input beam into the Spitfire Ti sapphire rod We recommended the Spitfire be pumped only with a Spectra Physics laser If this is not the case your Spitfire warranty may be voided unless prior written approval is obtained from Spectra Physics The pump laser must meet the following specifications Table 5 1 Pump Laser Specifications 1 kHz 5kHz Energy per pulse mJ 10 3 0 Average Power W 10 15 Wavelength nm 527 527 Beam Diameter nominal 6mm 6mm Energy Stability p p lt 2 lt 3 Beam Profile Multi mode uniform intensity Polarization Linear horizontal Versions of Spitfire amplifiers other than those listed in this manual may be pumped by other lasers In addition earlier Spitfire systems may be pumped by lasers such as the Spectra Physics Merlin Contact your Spectra Physics representative for more infor
85. neen eee eee een A 1 RS 232 Communication Protocols eee eeen A 1 Command Query Response Format eneen eee eeen A 2 Full Command Description onee eee en A 3 Limitations of RS 232 Control of the SDG II eee eee en A 5 Typical Command Usage sars aanta s arend Eder ine a HE BELG A 5 Appendix B Changing to from PicoMask Operati0N o oooooo B 1 A General Note on Changing Spitfire Versions enden enen enen eee B 1 Converting between PicoMask and Femtosecond Operation eneen eeen B 1 TOOIS REQUIFED nr waren atas Pa ede an vedan ea eer Bae See ae B 1 Changing the Spitfire PM to Femtosecond Operation enen enen eee B 2 Converting the Spitfire F to PicoMask Operation aen en eeen B 5 Appendix C Alignment tz ri etende A TR MWE EE a C 1 Try This First transit dew pean eae Dialed oe Re Lie dee ace eee he Pee eet Rt C 2 rools Reduredis nt einen beende ire heat ath debe tal eal are Wet D dte C 2 Stretcher Alignment Check eee eee eee A C 3 Compressor Alignment Check eee eee en C 3 Pump Beam Alignment 22 vaars ars betten Setesdal bee ed oe eet git C 4 Compressor Alignment eee eee ee eeen C 6 Ejecting the Pulse from the Amplifier eee C 7 Notes Report Form for Problems and Solutions Spitfire Ti Sapphire Regenerative Amplifer Systems List of Figures Figure 1 1 A typical layout showing the Spitfire pumping a Spectra Physics OPA 800CP 1 1 Figure 1 2 Block Diagram for the Spitfire F P
86. ng gt 1 5 W of average power at a wave length near 800 nm Use appropriate caution This procedure assumes that the grating block assembly is properly aligned as are the input beams into the stretcher and compressor and that the Spitfire is fully operational Under these circumstances the compressor requires only minimal adjustment for optimal performance 1 Disable OUT 1 DELAY and OUT 2 DELAY on the SDG II 2 Close the shutters of the pump laser and the seed laser Warning Failure to block the seed beam when called for in this procedure will result in significant damage to amplifier components Such damage is not covered by your warranty 3 Remove the covers from the Spitfire Carefully remove the grating block by removing the 14 20 or M3 screws depending on the Spitfire revision from the rotation stage If aligning a Spitfire SOFS compressor remove only the compressor grating 5 Install the removable reference iris in the X location see Figure C 4 and adjust the aperture opening to about 4 mm diameter HRR STRETCHER Stretcher E x Ma Grating 8 2 A 1 Compressor Grating COMPRESSOR Ms H OL 0 OL gt PT2 i em F Polarizer l REGENERATIVE AMPLIFIER Figure C 4 Alignment of beam into the compressor Alignment 6 Operate the Spitfire as a Q switched cavity dumped laser To do this enable OUT 1 DELAY and OUT 2 DELAY and adjust OUT 2 DELA
87. nge allows Ti sapphire lasers to pro duce and amplify optical pulses of extremely short duration As a corollary the same factors that allow Ti sapphire a broad tunable wavelength range might also affect the production and amplification of these ultrashort pulses 1 0 e u l Intensity arbitrary units 0 T 400 500 T T 600 700 800 T 900 1000 Wavelength nm Figure 3 2 Absorption and Emission Spectra of Ti Sapphire The Ti sapphire crystal is highly resistant to thermally induced stress This resistance allows it to be optically pumped at relatively high average pow ers without danger of fracture However it cannot handle the high peak powers that would result from directly amplifying femtosecond pulses A technique called Chirped Pulse Amplification which temporally stretches the pulse prior to amplification and then recompresses it following amplifi cation circumvents this limitation General Description Chirped Pulse Amplification How It Works When an intense beam travels through a Ti sapphire crystal it tends to self focus Self focusing is a nonlinear optical effect in which an intense light beam modifies the refractive index of the material it is passing through causing the beam to focus and intensify even further This can potentially result in a run away condition that causes permanent damage to the crystal Therefore self focusing makes it necessary to limit the peak power of a pul
88. norana mo 7 1 Stretcher and Compressor Beam Paths oenen eee 7 2 The Spitfire F Stretcher neee 7 3 The Spitfire F Compressor aaneen 7 4 viii Table of Contents Spitfire USF Stretcher and Compressor 0000 c cece eeen 7 5 Spitfire P Stretcher and Compressor 0000 cece tenes 7 5 Spitfire PM Stretcher and Compressor eneen eeen 7 5 Spitfire 50FS Stretcher and Compressor ane 7 6 The Ti Sapphire Regenerative Amplifier oee ee 7 7 Chapter 8 Maintenance and Troubleshooting 00000eeeeee ee ee eens 8 1 AY LISS FUS DEE 8 1 Cleaning Optic S i reiia rat oetan tinta ale Bi ag ee kate Bae e 8 2 TYOUDISSHOOUNG 2000 A Paty eS aed wage Bote Giese Seen a eee eee os 8 3 Symptom No Spitfire output eee ee 8 3 Symptom Regenerative Amplifier power is below specification eneen 8 3 Symptom Pulse has broadened out of specification oaeen 8 4 Symptom Output power or output spectrum is unstable nen eeen 8 4 Symptom Poor contrast ratio eneen eeen 8 5 Symptom Poor output beam quality eeen 8 5 Symptom Optical damage in the amplifier cavity eee eeen 8 5 Customer Service ane i srate nadat latend dion ae BE Qa ede edet veel ee he dee ied igs 8 6 Warranty oan o ea tee EN depen A tinal cna Dr Ae re Ee 8 6 Return of the Instrument for Repair neee 8 7 Service COnters eien narnia nein at aten Ea A ae ay Sid Boe A ge 8 8 Appendix A RS 232 Interface 00 0c eee eee eee A 1 RS 232 Connector Wiring e
89. ns to vertical polarization It passes through aperture A reflects off CM 6 and is reflected off the Ti sap phire surface and ejected out of the cavity Case c Input Pockels cell is off and then is turned on pulse is selected 1 The soon to be selected vertically polarized pulse reflects off CM 4 passes through aperture A through the inactive input Pockels cell and is rotated 45 as it passes through 4 It reflects off CM 5 and rotates another 45 as it passes through 4 again This time after the pulse passes back through the inactive Pockels cell and travels toward CM 6 the input Pockels cell is turned on The output Pockels cell remains off for now The pulse remains in the cavity because it remains horizontally polar ized Since the input Pockels cell is on the pulse is flipped 180 each time it traverses the input path leaving its polarization unchanged The pulse is then amplified each time it passes through the crystal The pulses that follow behind the selected pulse arrive with the input Pock els cell already turned on These following pulses remain vertically polarized as in Case b and are discarded After the selected pulse has passed through the crystal about 20 25 times 6 through 14 it has reached its optimum amplification The output Pockels cell is now turned on just before the pulse returns to it the precise timing is set by the SDG ID and the pulse now finds the output Po
90. nt and often complementary information When making burn patterns keep the sample of burn paper in a trans parent plastic bag in order to avoid getting residue on the optical sur faces Be careful to avoid reflections from the plastic A poor beam is an indication of optical damage or misalignment particu larly the alignment of the pump beam Refer to Appendix C for procedures to optimize pump beam alignment refer to Chapter 7 for a description of the pump beam path Make only small and reversible changes to the pump beam alignment The pump beam is tightly focused in the Ti sapphire rod in the amplifier and is easy to misalign Refer to Appendix C for a complete description of the pump beam alignment procedure It is recommended that you contact your Spectra Physics representative before making adjustments to the pump laser Operation Optimizing the Regenerative Amplifier Note g Danger Laser Radiation Use this procedure to minimize the time it takes for the amplified pulse to reach its peak level This build up time is compared to the time it takes for the Spitfire to amplify its own spontaneous emission in the absence of a seed pulse Minimizing this relative time for the pulse to be amplified is called build up time reduction Minimizing the build up time reduction is fundamental to optimizing the performance of the Spitfire In the following procedure the regenerative amplifier is init
91. nterlocks are cleared enable output status Periodically monitor the SDG II oy Nay ae A 5 Spitfire Ti Sapphire Regenerative Amplifer Systems A 6 Appendix B Changing to from PicoMask Operation A General Note on Changing Spitfire Versions It might be possible to change the output characteristics of a Spitfire ampli fier but conversion depends upon the amplifier model not all systems can be converted to other versions Refer to Chapter 1 for a complete descrip tion of the different versions of the Spitfire amplifier It is also possible with the proper sets of optics to extend the wavelength of the output of most versions to a portion of the range between 750 nm and 900 nm In addition if ordered from the factory with this option it is possible to change the output of most amplifiers to either 1 kHz or 5 kHz pulse repetition rate While most often straightforward it is possible that conversion between Spitfire models might require alignment techniques that are beyond the scope of this manual For more information about changing wavelengths or pulse repetition rates contact Spectra Physics Converting between PicoMask and Femtosecond Operation Spitfire PM systems are assembled and tested at the factory so that they can be transformed in the field to either a Spitfire F lt 130 fs pulse width or Spitfire USF lt 90 fs pulse width Similarly if ordered with this option a Spitfire F or Spitfire USF amplifier can be c
92. ompressor Stretcher Design 3 6 Because the GVD phenomenon described above is not a simple linear effect extra consideration must be given to a design intended to produce the shortest possible pulses The frequency components of a pulse travers ing an optical system experience dispersion that depends upon the square of the frequency In addition dispersion also results from higher order powers of the frequency For pulses around 100 fs or longer this higher order dispersion is small enough so that it is adequately compensated by the robust back to back design of the Spitfire stretcher compressor However for pulses of extremely short duration the higher order disper sion becomes large enough that additional compensation is required The Spitfire 5 0FS compensates for this higher order dispersion by using a mixed stretcher and compressor design the groove densities of the grat ings are different This requires that the gratings be adjusted independent of one another To provide this flexibility the Spitfire 50FS gratings are installed on separate mounts General Description The Spitfire PM Compressor Stretcher Design Some applications require amplified picosecond pulses rather than femto second pulses The Spitfire P system produces picosecond pulses from picosecond duration seed pulses such as those produced by the picosecond version of the Spectra Physics Tsunami The operation of the Spitfire P is based on the principals
93. on high reflector infrared output coupler picosecond or 10 second piezo electric transducer radio frequency saturable Bragg reflector standard cubic feet per hour self phase modulation transverse electromagnetic mode Titanium doped Sapphire ultraviolet wavelength xvii Unpacking and Inspection Unpacking Your System Your Spitfire laser amplifier was packed with great care and the containers were inspected prior to shipment Upon receiving the system immediately inspect the outside of the shipping containers If there is any major damage holes in the containers crushing etc insist that a representative of the carrier be present when you unpack the contents Instructions for unpacking the system are attached to the outside of the containers It is important that these instructions are followed carefully The system was precisely aligned at the factory then packed and shipped in a manner to preserve that alignment Handle the system with care while unpacking to preserve this condition Carefully inspect the laser system as you unpack it If any damage is evi dent such as dents or scratches on the covers or broken parts etc immedi ately notify the carrier and your Spectra Physics sales representative Keep the shipping containers If you file a damage claim they may be needed to demonstrate that the damage occurred as a result of shipping If the system is ever returned for service the specially designed container
94. onverted to a Spitfire PM which can produce picosecond pulses 2 ps pulse width when seeded by a femtosecond Mai Tai or Tsunami laser The necessary parts for conversion are included with each system This appendix lists the procedures for changing between these versions of the Spitfire amplifier Tools Required e hex driver for M3 for some versions of Spitfire e hex driver for 14 20 screws e hex driver for 0 050 in screws e 3 16 in hex driver e IR viewer B 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Changing the Spitfire PM to Femtosecond Operation Warning Do not attempt to clean the surfaces of the gratings or the gold coated W mirrors These optical surfaces can only be blown clean with dry nitro gen Attempting to clean these components will permanently damage them Do not allow anything to touch their surfaces Block the seed and pump beams or close the shutter on these lasers 2 Using the 7 16 in hex driver remove the mask assembly Figure B 1 that is in front of the gold mirror M in the stretcher Figure B 2 and Figure B 3 Do not loosen or move the block used to position the mask assembly leave it in place in order to return the mask assembly to its correct position when this procedure is reversed 0 136 0 354 mask number a 0 64 2 1 40 2 00 3 56 5 08 AA NS Y All dimensions in inches cm Figure B 1 Stretcher Mask Ta
95. or slide assembly behind the tall mirror M see Figure B 6 For picosec ond operation move the photodiodes closer together until the LEDs on the SDG 11 just flicker then slide them apart slightly until they produce a bright and steady glow b If either or both BWD LEDs are not brightly lit then slightly adjust gold mirror M up or down until both LEDs produce a bright and constant display c Compensate for any adjustment of M with the opposite adjustment of the tall mirror M so that the fourth pass of the beam in the stretcher is picked off by M Refer to the instructions in Chapter 6 for aligning the seed beam into the regenerative amplifier Use the IR viewer to check the pattern on the compressor grating Make sure the first and the last beam spots on the compressor grating are in a single vertical line If necessary translate the compressor stage to obtain the correct pattern The Spitfire should now be ready for picomask operation Appendix C Danger Laser Radiation Caution W Alignment Before starting these procedures it is essential that you read Chapter 2 Laser Safety and that you become thoroughly familiar with the compo nents and optical design of the Spitfire as discussed in Chapter 7 Use of controls or adjustments or performance of procedures other than those specified herein may result in hazardous radiation exposure The following procedures are not intended for the initial installa
96. ot selected and is rejected without passing through the Ti sapphire rod Case c the input Pockels cell is off when the pulse arrives but is turned on after the pulse travels through it and before the pulse is reflected back to the same cell The pulse is now selected In this case the pulse makes about 20 round trips in the cavity gaining in amplitude with each pass and is released into the compressor by the activation of the output Pockels cell As long as the selected pulse remains horizontally polarized it remains in the cavity Whenever a pulse arrives at the Ti sapphire crystal as verti cally polarized it is reflected off the surface and is not amplified Pulse selection is accomplished by using the polarization rotating proper ties of the passive 4 together with the input Pockels cell Pulses at kilo hertz rates are selected for amplification while the remaining megahertz seed pulses are rejected Control of pulse selection is determined by the SDG II as described in Chapter 4 Each of these three cases is now described in detail Case a the input Pockels cell is off and stays off pulse is rejected 1 The vertically polarized pulse reflects off CM 4 passes through aper ture Ay through the inactive input Pockels cell and is rotated 45 as it passes through 4 It reflects off CM 5 and rotates another 45 as it passes through 4 again 2 The pulse now horizontally polarized passes through the inact
97. ough The bandwidth of this stretched pulse is thereby reduced to that produced by a picosecond seed pulse If these reduced bandwidth pulses were allowed to pass through a stretcher designed for femtosecond pulses optical damage might result The band width of these masked pulses is much narrower than the bandwidth of fem tosecond pulses about Y2 nanometer as opposed to 10 nanometers This is also true for the picosecond seed pulses in the Spitfire P amplifier Picosecond pulses require a greater degree of dispersion to produce spatial and hence temporal separation This is achieved by increasing the path length of the beam in the stretcher and increasing the ruling density of the stretcher grating After amplification the stretched pulse is directed into the compressor which is configured just as it would be for a picosecond seed laser especially in the choice of compressor grating ruling and amplified picosecond pulses are the result A detailed description of the optical layout of the Spitfire PM is given in Chapter 7 Procedures for converting a Spitfire F or USF system to Spitfire PM operation or vice versa are given in Appendix B Changing to from PicoMask Operation Spitfire Ti Sapphire Regenerative Amplifer Systems Pulse Selection and Pockels Cells 3 8 Note Once the pulses leave the stretcher selecting a pulse for retention in the amplifier cavity is accomplished by exploiting its polarization characteris
98. output is deactivated the other outputs remain active OUT 1 DELAY display control and connector the display shows the selected delay 0 to 1275 ns between the pump laser Q switch sync signal and the time the input Pockels cell is turned on to capture the current seed pulse in the Spitfire amplifier The control knob adjusts the delay in 250 ps increments or 10 ns incre ments if the knob is pushed in during adjustment The corresponding BNC connector connects to the Spitfire s HSD 1 TRIG BNC connector This pro vides a low voltage sync signal to the high voltage driver which turns on the input Pockels cell to capture the current seed pulse OUT 2 DELAY display control and connector the display shows the selected delay 0 to 1275 ns between the pump laser Q switch sync signal and the time the output Pockels cell is turned on to eject the amplified pulse into the compressor This delay must be greater than the setting for OUT 1 DELAY The control knob adjusts the delay in 250 ps increments or 10 ns incre ments if the knob is pushed in during adjustment The corresponding BNC connector connects to the Spitfire s HSD 2 TRIG BNC connector This pro vides a low voltage sync signal to the high voltage driver which turns on the output Pockels cell to eject the amplified pulse SYNC OUT DELAY display control and connector the display shows the selected delay 0 to 1275 ns between the time the output Pockels cell is fired and the
99. output power Verify the cavity beams are parallel to the chassis top surface measure the mirror leakage beam height from the chassis surface outside the cavity behind CM and CM and correct any error It is likely that the beam height beyond CM is either too high or too low To correct any error make vertical adjustments to CM while com pensating for power and mode shape with vertical adjustments to CM until the correct beam height is restored Laser radiation is present Beware the eye hazard from the residual pump beam behind CM 15 16 17 Repeat Step 14 for the beam between CM and CM Adjust CM for beam height behind CM and compensate for output power and mode shape with CM Reposition both intracavity apertures coaxially about the beam as fol lows Open each aperture fully then reduce the diameter of each iris The beam should be symmetrical around the iris as it is reduced pass ing through its center If it is not loosen the screw that retains the aper ture post and center the iris about the 800 nm intracavity beam Open both intracavity apertures and record the output power The pump laser beam should now be optimally aligned C 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Compressor Alignment Danger In the following procedure the regenerative amplifier is initially oper AAM ated as an optically pumped Q switched laser In this configuration the Spitfire is capable of produci
100. pit fire system While this manual contains a brief installation procedure it is only a guide to preparing the site for the initial set up of the Spitfire system Please wait for the Spectra Physics service engineer to install the system as part of your purchase agreement Only personnel authorized by Spectra Physics can install and set up your Spitfire system Operation describes the routine operation of the Spitfire It is followed by a detailed description of the beam path and internal adjustments of the amplifier This information is needed should it become necessary to per form a simple re alignment of the system using the procedures described in this manual A full alignment of the system should only be performed by an authorized Spectra Physics representative The Maintenance and Troubleshooting section contains maintenance procedures that will allow you to keep your Spitfire clean and operational on a day to day basis It also contains procedures you can perform to rem edy any minor problems that might be encountered Also included are pro cedures to help you guide your Spectra Physics field service engineer to the source of any major problems Do not attempt repairs yourself while the unit is still under warranty instead report all problems to Spectra Physics for warranty repair This section includes a replacement parts list plus a list of world wide Spectra Physics service centers you can call if you need help This p
101. pitfire F Stretcher Beam Path The vertically polarized seed beam is first routed through the Faraday iso lator 1 2 3 before entering the stretcher 1 To enter the stretcher the seed beam passes through a gap in the verti cal retroreflector VRR 4 and over the pick off mirror M 5 The grating spreads the beam spectrally 6 and directs the broadening beam onto the center of the concave gold mirror M 7 The grating mount has a single adjustment that rotates the grating to change the angle of incidence of the beam The stretcher grating shares its mount with the compressor grating M is angled slightly upward to reflect the beam over the grating 8 onto the tall stretcher end mirror M The concave gold mirror and the tall stretcher end mirror have vertical and horizontal adjustments M2 reflects the beam back over the grating to M 9 which returns it to the grating 10 The grating reflects the collimated beam toward the bottom of the ver tical retroreflector VRR 11 Notice that the path of the redder wave lengths is longer than that of the bluer wavelengths and therefore lags behind the bluer wavelengths The beam now retraces its path back through the stretcher VRR 12 reflects the beam back to the top of the grating The spectrum is tem porally spread even further as the redder wavelengths again take the longer path Passing the beam through the stretcher one more time 13 14 15 16 it is focused bac
102. r in this chapter function properly Also make sure that all warning labels remain firmly attached CDRH Requirements for Operating the Spitfire Using the Optional PC Control The Spitfire system complies with all CDRH safety standards when oper ated using the SDG IJ controller However when the laser is operated from a computer using the command language described in Appendix A RS 232 Interface the following must be provided in order to satisfy CDRH regulation requirements An emission indicator that indicates laser energy is present or can be accessed It can be a power on lamp a computer display that flashes a statement to this effect or an indicator on the control equip ment for this purpose It need not be marked as an emission indicator so long as its function is obvious Its presence is required on any con trol panel that affects laser output including a computer display panel Spitfire Ti Sapphire Regenerative Amplifer Systems CE CDRH Radiation Control Drawings Refer to the warning labels in Figure 2 4 Pump Laser Input Port Seed Laser Input Port Input Panel Amplified Pulse Spitfire Amplifier Alignment Laser Input Port On Off Switch and Power Cord Connector Synchronization and Delay Generator SDG II Back Panel Figure 2 3 CE CDRH Radiation Control Drawing Laser Safety CE CDRH Warning Labels SPECTRA PHYSICS LASERS P O BOX 7
103. raining Laser Safety Standards Safe Use of Lasers Z136 1 American National Standards Institute ANSI 11 West 42 Street New York NY 10036 Tel 212 642 4900 Occupational Safety and Health Administration Publication 8 1 7 U S Department of Labor 200 Constitution Avenue N W Room N3647 Washington DC 20210 Tel 202 693 1999 Internet www osha gov A Guide for Control of Laser Hazards American Conference of Governmental and Industrial Hygienists ACGIH 1330 Kemper Meadow Drive Cincinnati OH 45240 Tel 513 742 2020 Laser Institute of America 13501 Ingenuity Drive Suite 128 Orlando FL 32826 Tel 800 345 2737 Internet www laserinstitute org Compliance Engineering 70 Codman Hill Road Boxborough MA 01719 Tel 978 635 8580 International Electrotechnical Commission Journal of the European Communities IEC60825 1 Safety of Laser Products Part 1 Equipment Classification Requirements and User s Guide IEC 309 Plug Outlet and Socket Coupler for Industrial Uses Tel 41 22 919 0211 Fax 41 22 919 0300 Internet www iec ch Cenelec European Committee for Electrotechnical Standardization 35 Rue de Stassartstraat B 1050 Brussels Belgium Tel 32 2 519 68 71 Internet www cenelec org Spitfire Ti Sapphire Regenerative Amplifer Systems Document Center Inc 111 Industrial Road Suite 9 Belmont CA 94002 4044 Tel 650 591 7600 Internet www document center com Equip
104. rative amplifier as a temporary solution Optimize the seed laser beam alignment Optimize the pump laser power according to its user s manual Optimize the alignment of the pump laser beam Refer to Appendix C Check the settings for OUT 1 DELAY and OUT 2 DELAY on the SDG Il Spitfire Ti Sapphire Regenerative Amplifer Systems Symptom Pulse has broadened out of specification Possible Cause Corrective Action Compressor delay not be optimized Seed laser pulses are broadened Pump laser power is low or unstable Stretcher misalignment is broadening pulses Pockels cells timing is incorrect Optical components are damaged Wings are present on output autocorrela tion Adjust the compressor motor controller to get the shortest pulse Check the seed laser bandwidth and center wavelength See troubleshooting guide in the pump laser user s manual Check the alignment of the stretcher Verify the seed laser beam alignment is optimized Check the settings for OUT 1 DELAY and OUT 2 DELAY Contact your Spectra Physics representative Check the seed laser bandwidth and center wavelength Make certain that stretcher mirror M is at focal point of large gold mirror M Verify the compressor grating is parallel to the stretcher grating coupled grating mount systems only not applicable to the Spitfire 50FS Contact your Spectra Physics representative if this is not the case Verify the beam is not clippin
105. re to remove the iris when called for in this procedure will result in significant damage to Spitfire components Such damage is not covered by your warranty 23 The compressor alignment should now be optimized If this is not the case contact your Spectra Physics service engineer Ejecting the Pulse from the Amplifier After performing the alignment procedures above it will be necessary to adjust the timing of the Pockels cells to achieve proper capture and ejection of pulses from the amplifier Refer to Chapter 6 for this procedure C 7 Spitfire Ti Sapphire Regenerative Amplifer Systems C 8 Notes Notes 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Notes 2 Notes Notes 3 Spitfire Ti Sapphire Regenerative Amplifer Systems
106. roduct has been tested and found to conform to Directive 89 336 EEC for Electromagnetic Compatibility Class A compliance was demon strated for EN 50081 2 1993 Emissions and EN 50082 1 1992 Immu nity as listed in the official Journal of the European Communities Refer to CE Declaration of Conformity Low Emissions on page 2 7 Every effort has been made to ensure that the information in this manual is accurate All information in this document is subject to change without notice Spectra Physics makes no representation or warranty either express or implied with respect to this document In no event will Spectra Physics be liable for any direct indirect special incidental or consequential dam ages resulting from any defects in this documentation If you encounter any difficulty with the content or style of this manual please let us know The last page is a form to aid in bringing such problems to our attention Thank you for your purchase of Spectra Physics instruments Environmental Specifications CE Electrical Equipment Requirements For information regarding the equipment needed to provide the electrical service listed under Required Utilities on page 5 3 please refer to speci fication EN 309 Plug Outlet and Socket Couplers for Industrial Uses listed in the official Journal of the European Communities Environmental Specifications FCC Regulations The environmental conditions under which
107. ror of the amplifier Danger The alignment laser input port must be closed while either the Spitfire or A Laser Radiation the pump or the seed lasers are operating The Synchronous Delay Generator The Synchronous Delay Generator SDG II controls the selection of pulses from the seed laser and the repetition rate of the pulsed output of the Spitfire It acts as a counter that counts and then selects mode locked seed pump pulses at either the 1 kHz or the 5 kHz amplifier rate The SDG IJ also synchronizes the seed pulses with pulses from the pump laser it captures the next seed pulse while the laser rod is still excited by the pump pulse It does this by providing an adjustable delay in nanosec onds that the amplifier input Pockels cell can be set to in order to capture the pulse The second adjustable delay controls the output Pockels cell to eject the pulse into the compressor after it has been amplified The SDG H allows the output repetition rate to be reduced from its pre set value by dividing 4 3 Spitfire Ti Sapphire Regenerative Amplifer Systems Front Panel the input synchronization signal from the pump laser Preset integer divider values are provided The third adjustable delay provides a trigger for laboratory equipment such as the horizontal sweep of a high speed oscilloscope The SDG II also contains the high voltage power supplies for driving the Pockels cells for 1 kHz systems 5 kHz systems use an addition
108. roviding the best equipment for the money and second by offering service facilities that get your instrument repaired and back to you as soon as possible Spectra Physics maintains major service centers in the United States Europe and Japan Additionally there are field service offices in major United States cities When calling for service inside the United States dial our toll free number 1 800 456 2552 To phone for service in other coun tries refer to the section Service Centers on page 8 8 Order replacement parts directly from Spectra Physics For ordering or shipping instructions or for assistance of any kind contact your nearest sales office or service center You will need your instrument model and serial numbers available when you call Service data or shipping instruc tions will be promptly supplied To order optional items or other system components or for general sales assistance dial 1 800 SPL LASER in the United States or 1 650 961 2550 from anywhere else This warranty supplements the warranty contained in the specific sales order In the event of a conflict between documents the terms and condi tions of the sales order shall prevail Unless otherwise specified all parts and assemblies manufactured by Spectra Physics are unconditionally warranted to be free of defects in workmanship and materials for a period of one year following delivery of the equipment to the F O B point Liability under th
109. s assure adequate protection Warning Spectra Physics considers itself responsible for the safety reliability and performance of the Spitfire amplifier only under the following condi tions e All field installable options modifications or repairs are performed by persons trained and authorized by Spectra Physics e The equipment is used in accordance with the instructions provided in this manual System Components The system is shipped in two separate containers e One contains the Spitfire assembly e One contains the SDG II controller and accessory kit see below xix Spitfire Ti Sapphire Regenerative Amplifer Systems Accessory Kit XX Included with the laser system is this manual a packing slip listing all the components shipped with this order and an accessory kit containing the following items e cables kit e SDG II controller e DC motor controller and AC adapter e 4 chassis clamps e beam tubes for the pump laser e 2 routing mirror assemblies for the beam from the seed laser Chapter 1 Introduction The Spectra Physics Spitfire system amplifies individual laser pulses that are selected from a stream of pulses and produced by a separate mode locked Ti sapphire laser Typically an input pulse with an energy of only a few nanojoules can be amplified to about 1 millijoule Specific Spitfire models can amplify pulses ranging in duration from less than 50 femto seconds up to about 80 picosecon
110. s in the Spitfire F Stretcher and Compressor Note g 7 2 The different versions of the Spitfire have different stretcher and compres sor designs as a result of their different pulse widths Basically each ver sion uses its own set of gratings that are set at different angles to the beam There are also other relatively minor differences Although your version of the Spitfire may differ slightly study the beam path through the Spitfire F model Differences in the design of the stretcher compressor in the other versions are described relative to the Spitfire F in later sections After passing through the Faraday isolator the seed laser beam is horizon tally polarized and remains so in the stretcher The polarization of the beam is changed in the amplifier but when it enters the compressor it is again horizontally polarized Numbers are used in the following drawings to track the path of the beam as it passes from optic to optic The numbers are not used either to name the optic itself or to indicate the position of the beam Refer to Figure 7 1 for the abbreviations used to name components in the stretcher and com pressor Shorter and longer wavelengths strike the optical components in the stretcher and compressor at different locations Figure 7 2 shows how the wavelengths are separated The Spitfire F Stretcher The Spitfire Beam Path Seed Input zen Redder Figure 7 2 S
111. s that produce a wide range of pulse durations Table 1 1 lists the models covered by this manual Each Spitfire model operates at either a 1 kHz or 5 kHz pulse repetition rate and can be ordered preset to either rate Systems may also be converted from one models to another Contact your Spectra Physics representative for more information about these options Most of the configurations listed in Table 1 1 are also available with a high power option the Spitfire HP that operates at 1 kHz Spitfire HP systems add extra length to the head assembly to accommodate a second stage of amplification These high power systems are described in separate docu mentation Contact your Spectra Physics representative for more informa tion Table 1 1 Spitfire Configuration Matrix Amplifier Pulse Width Description Model Spitfire F lt 130 fs standard version Spitfire P lt 2 ps produces picosecond pulses using a pico second seed laser Spitfire PM lt 2 ps pico mask version produces picosecond pulses using a femtosecond seed laser Spitfire USF lt 90 fs simple reconfiguration for shorter pulses Spitfire 50FS lt 50 fs ultra short output pulses All versions of the Spitfire listed in Table 1 1 with the exception of the Spitfire SOFS are available in three standard wavelength ranges as deter mined by the optics set used The Spitfire 50FS is available only with Optics Set 1 Table 1 2 Spitfire Optics Sets Optics S
112. se in the Ti sapphire crystal to less than 10 GW cm Chirped Pulse Amplification CPA allows a Ti sapphire crystal to be used to amplify pulses beyond this peak power while keeping the power density in the amplifier below the damage threshold of the crystal CPA is accom plished in three steps The first step stretches the very short seed pulse that is supplied by a stable mode locked picosecond or femtosecond laser Stretching the pulse i e increasing its duration reduces its peak power which greatly reduces the probability of damage to the Ti sapphire ampli fier crystal The second step amplifies the stretched pulse a pump laser provides a syn chronous energy pulse to the Ti sapphire crystal to excite it just prior to the arrival of the stretched seed pulse The seed pulse causes stimulated emis sion which amplifies the pulse at the same wavelength and direction This is in contrast to spontaneous emission within the gain medium that typi cally is amplified to become laser output in other systems The third step recompresses the stretched amplified pulse as close as pos sible to its original duration The fundamental relationship that exists between laser pulse width and bandwidth is that a very short pulse exhibits a broad bandwidth and vice versa For a Gaussian pulse this relation is given as dv dt gt 0 441 1 where dv is the bandwidth and dt is the laser pulse width For example for a 100 fs duration puls
113. stments If the Spitfire is not producing amplified pulses first verify the following e there is sufficient pump power e the pump beam has not become misaligned e the SDG II OUT 2 DELAY is sufficiently greater than OUT 1 DELAY e the 5VDC ENABLE switch on the SDG II back panel is in the disabled or down position e the Pockels cells are properly connected triggered and operating e the intracavity apertures are not blocking the beam If these criteria are all met inspect the internal optics for cleanliness and damage Use the procedure below to clean optics as needed Heed the warnings regarding cleaning Not all optical surfaces can be cleaned other than by blowing dust off with dry nitrogen If the troubleshooting and corrective procedures in this chapter do not solve the problem please contact your Spectra Physics representative before tak ing further action Contact information is included in Customer Service on page 8 6 8 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Cleaning Optics Warning W The Spitfire has been designed for minimal maintenance However from time to time depending on the laboratory environment it may be necessary to clean the optics The following materials are required e Reagent grade methanol or acetone e Lens tissues e Hemostat surgical pliers e Eyedropper Do not attempt to clean the surfaces of the gratings and the gold coated mirrors These optical surfaces can on
114. t up a beam dump to capture the laser beam and prevent accidental exposure Figure 2 2 2 1 Spitfire Ti Sapphire Regenerative Amplifer Systems Caution W Safety Devices 2 2 VISIBLE AND OR INVISIBLE VISIBLE AND OR INVISIBLE LASER RADIATION LASER RADIATION AVOID EYE OR SKIN EXPOSURE TO AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION DIRECT OR SCATTERED RADIATION CLASS 4 LASER PRODUCT WAVELENGTH S POWER WAVELENGTH S AND PULSE WIDTH DEPEND ON PUMP OPTIONS AND LASER CONFIGURATION CLASS IV LASER PRODUCT SEE MANUAL 0451 8080 POWER PULSE WIDTH DEPEND Ol OPTIONS AND LASER FIGURATION Figure 2 1 These CE and CDRH standard safety warning labels would be appropriate for use as entry warning signs EN 60825 1 ANSI Z136 1 Section 4 7 Figure 2 2 Folded Metal Beam Target Use of controls or adjustments or the performance of procedures other than those specified herein may result in hazardous radiation exposure Follow the instructions contained in this manual for safe operation of your laser At all times during operation maintenance or service of your laser avoid unnecessary exposure to laser or collateral radiation that exceeds the accessible emission limits listed in Performance Standards for Laser Prod ucts United States Code of Federal Regulations 21CFR1040 10 d Because the Spitfire cannot generate output energy without being pumped and seeded by
115. t von sichtbarer Radiaci n l ser visi Zichtbare en of Warning et ou invisible exposi und oder unsicht ble y o invisible Evi onzichtbare laser Label tion dangereuse de barer Laserstrahl tar la exposici n de straling Vermijd 1 l il ou de la peauau ung Augen und los ojos ola piel ala blootstelling aan rayonnement direct Hautkontakt mit radiacion ya sea ogen of huid door ou diffus Appareil a direkter Strahlung directa difusa Pro directe of gereflect laser de Classe 4 oder Streustrahlung ducto l ser Clase IV eerde straling Klasse Puissance maximum vermeiden Laser Potencia m xima lt 5 4 laser produkt 532 5 W Longueur Klasse IV Maximale W Longitud de onda nm maximaal uittre D onde 700 1000 Ausgangsleistung lt 700 1000 nm Longi dend vermogen nm Duree d impul tud de pulso 30 fs 6 15 W sion 30 fs 6 ps Wellenlange 700 ps zie handleiding 1000 nm Pulsbreite 30 fs 6 ps CE Exposition Dan Nicht dem Strahl aus Evitar exponerse j Vanuit dit apertuur Aperture gereuse Un Rayon setzen Austritt von Atraves de esta aper wordt zichtbare en Label nement laser visible sichtbarer und oder tura se emite radia onzichtbare lasers 3 et ou invisible est unsicht barer Laser cion laser visible y o traling geemiteerd emis par cette ouver strahlung invisible Vermijd blootstelling ture CE Rayonnement Laser Sichtbare und oder Al abrir y retirar el Zichtbare en onzicht Inter Visible et ou Invisible unsichtb
116. tems Recommended Diagnostic Equipment Tools Required 5 4 The following equipment is recommended for day to day operation of the Spitfire a power meter capable of measuring between 10 mW and 20 W aver age power e g Ophir Scientec Molectron from 500 nm to 900 nm a fast CRT analog oscilloscope capable of 300 MHz or better e g a Tektronix 2467 7104 or 2465 a fast photodiode with a 2 ns rise time or better e g an Electro Optics Technology Model ET 2000 IR viewer and IR card an autocorrelator e g a Spectra Physics Model SSA In addition the following equipment should also be available during instal lation maintenance and or troubleshooting a small low divergence HeNe laser for alignment two broadband mirrors and mounts for aligning the HeNe to the sys tem The following tools may be needed during installation maintenance and or troubleshooting three gimbal mounts with 4 6 in adjustable height alignment pins 10 in 25 cm scale three silver mirrors for the above mounts 1 Phillips screwdriver white business card trim pot screwdriver lens tissue standard U S hex ball driver set English and metric scales rulers gel linear polarizing film Preparing for Installation Interconnect Diagrams The figures below are schematic representations of the main signal and control connections between components of the Spitfire 1 kHz Figure 5 1 and 5 kHz systems Figure 5 2 For clarity t
117. the laser system will function are listed below For indoor use only Altitude up to 2000 m Temperatures 10 C to 40 C Maximum relative humidity 80 non condensing for temperatures up to 31 C Mains supply voltage do not exceed 10 of the nominal voltage Insulation category I Pollution degree 2 This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to Part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equip ment generates uses and can radiate radio frequency energy and if not installed and used in accordance with this instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense Modifications to the laser system not expressly approved by Spectra Physics could void your right to operate the equipment Table of Contents Preface Tinner id pheasant hee hed nee aka eee ate iii Environmental Specifications 00 e eee eee v CE Electrical Equipment Requirements enen eee v Environmental Specifications onee eee v FCC Regulations iiipin zvn oet oie AA Boa Go Bee eee See aad deen v Warning Conventions a cei esc eee nwe nnn ad wn
118. tion of the Spitfire amplifier Call your Spectra Physics service representative to arrange an installation appointment which is part of your purchase agreement Allow only authorized Spectra Physics representatives to install your laser You will be charged for repair of any damage incurred if you attempt to install the system yourself and such action may void your warranty These procedures are supplied as a convenience in the event your Spitfire system is out of warranty and a service call is problematic These advanced procedures might well result in loss of function or even permanent damage to the system if performed by personnel not trained by Spectra Physics If the amplifier is no longer lasing or if an intracavity optical component is seriously misaligned or damaged and must be replaced contact your Spectra Physics representative before attempting any repair Experienced experts may be able to apprise you of techniques that might save you con siderable time and expense in these circumstances More advanced procedures such as replacing a damaged Ti sapphire rod in the amplifier will require a service call Essential to proper Spitfire amplifier operation is the alignment of the seed laser into the Spitfire amplifier optimization and other similar adjustments These are considered routine and are described in Chapter 6 Operation If the amplifier is operating properly with the installed optics set but oper ation at a dif
119. ust and drafts and does not exhibit any large temperature fluctuations Room temperature should be maintained to within 2 C during operation e For stability the entire system should be placed on a single standard optical table e Because occasional adjustments might be required to optimize perfor mance position the Spitfire to allow easy access to its internal con trols e Place the seed laser as close as possible to the Spitfire to avoid beam instability problems such as those caused by unstable routing mirrors or by too many mirrors Only use stable routing mirrors e Do not leave exposed any laser beam that travels more than 3 inches 7 5 cm e Both the pump laser and mode locked seed laser must operate within the specifications listed earlier The Spitfire is shipped pre assembled but some optics have been removed and carefully wrapped for protection during shipment Leave them wrapped at this time The Spectra Physics representative assigned to per form the initial installation will unwrap and install these optics The Spitfire requires access to 110 120 Vac 15 A single phase power The seed and pump laser systems have electrical and cooling requirements as well Before beginning installation refer to the user manuals for those units Make sure proper service is available at the site before the Spectra Physics field technician arrives for the initial installation 5 3 Spitfire Ti Sapphire Regenerative Amplifer Sys
120. ut Pockels cell ejects the amplified pulse into the compressor Fol lowing the synchronization of the input Pockels cell there is a delay before the output cell is activated to ensure the captured pulse is released at opti mum amplification This delay is adjustable from O to 1275 ns which allows the pulse to complete the amplifier cavity path an integral number of times The SDG JI is first triggered by a TTL positive edge pulse provided by the pump laser It then produces separate triggers with adjustable delays for both Pockels cells OUT 1 DELAY on the front panel connects to the input Pockels cell OUT 2 DELAY connects to the output Pockels cell Delay adjustment is via the corresponding knobs on the front panel and each delay is displayed in nanoseconds above each knob Adjusting OUT 3 DELAY allows the user to synchronize target or monitoring devices to the Spitfire output pulse As a simplified example OUT 3 DELAY can be used to provide horizontal triggering for an oscilloscope The repetition rate of Pockels cell switching and hence the repetition frequency of the Spitfire output is dependent on the repetition rate of the input trigger from the pump laser For 1 kHz systems the SDG II also contains the high voltage power sup plies used to power the Pockels cells 5 kHz systems use a separate high voltage power supply The SDG II contains the control and the signals for the Bandwidth Detector BWD The control of the B
121. wall by the tall stretcher mirror B 5 Spitfire Ti Sapphire Regenerative Amplifer Systems Note g Warning W The configuration of the mask mount differs depending on the date of manufacture of the Spitfire Take care that the Allen wrench or hex driver doesn t touch the grating surface which is close to the mounting screws 10 11 12 Loosen the two 14 20 screws that secure the rotation stage and slide the stage backward to the picosecond position as marked on the base plate of the amplifier assembly see Figure B 4 Tighten the two 4 20 screws to secure the rotation stage in the pico second position Place the Spitfire PM picosecond grating assembly on the rotation stage and secure it using the two mounting screws removed in Step 3 Unblock or unshutter the seed laser and allow the seed beam to enter stretcher Check the alignment of the beam through the mask The beam reflects from mirror M multiple times Make sure that only the top beam is clipped by the top narrow notch of the mask Be certain that the spec trum reflected back from M is centered on the notch of the mask Using the IR viewer rotate the grating stage until the correct picosec ond pattern on the stretcher grating is observed Next adjust the BWD photodetectors for the new pulse bandwidth in the stretcher while observing the signals for PD and PD on the SGD II a Loosen the 0 050 in setscrews on top of the photodetect
122. yo 153 0061 Telephone 81 3 3794 5511 Fax 81 3 3794 5510 Japan West Spectra Physics KK West Regional Office Nishi honmachi Solar Building 3 1 43 Nishi honmachi Nishi ku Osaka 550 0005 Telephone 81 6 4390 6770 Fax 81 6 4390 2760 The Netherlands Telephone 31 0900 5 55 56 78 United Kingdom Telephone 44 1442 258100 United States and Export Countries Spectra Physics 1330 Terra Bella Avenue Mountain View CA 94043 Telephone 800 456 2552 Service or 800 SPL LASER Sales or 800 775 5273 Sales or 650 961 2550 Operator Fax 650 964 3584 e mail service splasers com sales splasers com Internet www spectra physics com And all European and Middle Eastern countries not included on this list And all non European or Middle Eastern countries not included on this list Appendix A RS 232 Interface Most functions of the SDG II can be controlled by any computer with a standard RS 232 serial port The RS 232 command syntax described here is designed to replicate the functions of the front panel controls and read outs of the SDG II controller RS 232 Connector Wiring The SDG II serial port accepts a standard 9 pin D sub connector male female extension cable for hookup Only three pins on the connector are used for serial communications Pin Number Function 2 SDG Il transmit data computer receive data 3 SDG Il receive data computer transmit data 5 Signal ground

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