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GWU versaScan - Spectra

1. 5 15 for wavelength adjustment to change the versaScan output wavelengths The scale on the micrometer is not fixed to the output wavelengths The relation between the scale on the micrometer and the versaScan wavelength is a non linear function Once the versaScan is set up and aligned it is possible to calibrate the scale on the micrometer Just let the system warm up enough and measure the signal wavelength and note down the corresponding micrometer position When measuring the signal wavelength the corresponding idler wavelength can be obtained through the following relation see as well fig 2 in chapter 3 Specifications of the versaScan 1 Midier 1 A4 pump 1 Asignal 38 GWU Lasertechnik ML Which follows directly out of the energy conservation Opump Osignal Oidler This calibration is valid as long as the alignment and set up of the pump laser and the versaScan has not changed The versaScan wavelength is depending on the beam direction of the three interacting waves pump signal idler relative to the crystal optical axis Thus the angle under which the crystal is fixed inside the holder as well as the pump beam direction and the alignment of the versaScan resonator mirrors are affecting the output wavelengths The typical pointing stability specification of many pump lasers 100 urad is such that if the pump laser changes its beam direction by 1 time its specified range then the versaScan wavelength c
2. 2 Label types German Label 1 Part no 902107 Label 3 Part no 902100 VISIBLE pren INVISIBLE R RADIATION DIRECT OR SCATTERED RADIA POWER W wma nae age WIDTH pote OPTIONS AND LASER C CLASS IV LASER PRODUCT Label 5 Part no 902101 Label 2 Part no 902103 Label 4 Part no 902102 Label 6 Part no 902105 ML GWU Lasertechnik ML 2 Pump laser requirements 355 nm 5 ns 9 ns shorter pulse length on request up to 30 Hz higher repetition rates on request homogenous beam profile without hot spots 1cm pump beam divergence versaScan BB lt 0 5 mrad full angle at 355 nm versaScan MB 0 8 mrad full angle possible is up to 1 5 mrad for BB and up to 3 mrad for MB with reduced output and energy stabilit polarization horizontal 3 Specifications of the versaScan dimensions Lx W 285 x 100 mm2 H 142 mm feet Standard feet 35 nm 10 mm Feet elongations 40 mm 55 mm and 82 mm available non linear crystal versaScan MB Type II pump energy density lt 0 65 J cm recommended 0 5 J cm 0 6 J cm adjustable by the use of appropriate telescope lenses tuning range signal wave 410 nm 709 nm idler wave 710 nm 2630 nm hreshold fluence lt 0 2 J cm total efficiency signal typically gt 20 at 435 nm 2000 nm idler for pump energies gt 80 mJ pulse 355 nm pulse duration energy ratio signal idler typical spectral width depending
3. SHG stage For a versaScan BB HE and for a versaScan MB build up the OPO in some distance to the pump laser Choose the distance between the pump laser and the versaScan in a way that the reflection from the versaScan output coupler figure 5 9 does not overlap with the laser pulse at the THG crystal of the pump laser The light propagates 30 cm each 1 ns Thus for 5 ns pump pulse length for example the geometrical spread of the pump pulse is 5 x 30 cm 150 cm and hence the distance between the THG crystal and the OPO resonator should be 150 cm 2 75 cm In general the distance between the laser THG crystal inside the laser housing and the versaScan output coupler figure 5 9 should be Pulse length of the pump laser in ns x 15 cm This is usually fulfilled for a typical distance between the pump laser housing and the versaScan housing of about 30 cm 40 cm 6 1 1 LBP AR coated UV filter For pump laser output power of up to 3 6 W at 355 nm e g 360 mJ at 10 Hz 3 6 W the LBP is consisting of an AR coated UV filter AR 1064 nm 532 nm Just place the UV filter inside the pump laser housing into the laser beam and make sure that it is tilted against the pump laser beam a little bit 8 to 10 DEG that its back reflection does not enter the YAG rod As well let the UV filter have a tight contact to some metal parts e g hold it in a metal ring for cooling purpose Otherwise the heated up filter may break After installing the
4. and dry place if itis not used for a longer time Preferably use a desiccator for storage Centre the crystal in the crystal holder with the upper side to the spring amp pressure plate inside the crystal holder fig 8 Fix the crystal in the holder by loosening the setscrew metric M4 fig 8 carefully The pressure of the spring is now holding the crystal Install the crystal holder to the rotation stage Fasten the laser safety beam shield fig 5 3 above the crystal rotation stage 6 5 2 Check if the beam is clipped by the crystal e f present take out the first signal idler separator mirror or the alternative polarizing beam splitter cube by loosening the screw fig 5 22 e Take out the output coupler holder with the output coupler fig 5 9 and the UV filter fig 5 17 therein as well Loosen the screw fig 5 11 to take out this holder If the OPO resonator is already aligned it is alternatively possible to take out the UV filter only by loosening the setscrew figure 5 17a e llluminate the crystal with the pump beam at the lowest power available and watch the transmitted pump beam with a white paper sheet The beam should pass through the middle of the crystal e Rotate the crystal with the micrometer screw fig 5 15 or if present with the optional motor The beam should not be clipped for the tilted crystal Laser safety The laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 mu
5. better then 80 90 To avoid these losses this dichroic separator mirror can be taken out Since there is no outlet to couple out the signal radiation out of the versaScan MB housing you need to take off the rear cover plate of the versaScan MB or drill a hole into it 9 2 3 4 Non collinear versaScan alignment lf the versaScan is well aligned like described in chapter 7 or 8 then the signal and idler waves are collinear overlapping spatial It is possible to align the versaScan non collinear as well Then the signal and idler waves are not collinear and both beams are separated in some distance behind the versaScan The specified beam pointing stability of the versaScan is only obtained for the collinear alignment For non collinear alignment the beam direction of the signal and idler wave may slightly change when changing the wavelength Typically this change is less than the divergence of the beams such that it is not remarked by the user This non collinear alignment can be achieved by tilting both versaScan resonator mirrors against the pump beam and then fine align only one of the two resonator mirrors until the size of the visible signal spot is minimized This can be observed best on a black screen about 2 m behind the versaScan 9 2 4 Degeneracy Degeneracy defines the situation when the signal wavelength and the idler wavelength are the same This is at the versaScan output wavelength of 709 4 nm which is just 2 times the pu
6. 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 12 GWU Lasertechnik ML 4 Important precautions The versaScan should only be operated with all its covers closed and fixed Laser safety When opening the cover e g for alignment ensure that the laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 is in place any time pump laser light is entering the versaScan Otherwise harmful reflections from the tilted BBO crystal will put the user at high risk Avoid any optical or mechanical damage of the optical componenis Do not touch the optical components Wear gloves or use weak plastic tweezers to hold optical components Ensure that the surfaces of the optics are free from dust Particles burned onto the dielectric coatings of the mirrors or the crystal surfaces can lead to reduced output energies Dust particles and pollutants should be removed by blowing clean air onto the surfaces Never blow your wet breath onto the optics Never use acetone to clean the BBO crystals lf the versaScan will not be in use for a long period of time we recommend to store the BBO crystal in a clean and dry place For transport and delivery the BBO is packed in a small plastic transparent transportation container which protects the crystal from mechani
7. on pump pulse length versaScan BB for versaScan BB HE add 10 See figures 3 and 4 versaScan MB 4 cm for 7 ns pump pulse length 7 cm for 4 ns pump pulse length typical divergence depending on pump pulse length versaScan BB signal wave 2 5 mrad 8 mrad divergent idler wave 3 5 mrad 10 mrad focussing convergent versaScan MB horizontal 0 7 mrad signal and idler waves vertical signal 3 mrad 9 mrad divergent idler 4 mrad 11 mrad focussing convergent polarization vertical exception The idler wave of versaScan MB is horizontal GWU Lasertechnik ML 100 90 100 total versaScan pulse energy Signal Idler 80 z 70 gt g 60 D 50 w 40 O E 30 Idler oO n 20 degeneracy 10 709 4 nm 0 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 wavelength nm Figure 1 Distribution of the versaScan pulse energy between Signal and Idler O FO pump Signal Idler 1 1 A 1 A pump Signal nm Idler sig Signal wavelength 2 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 Idler wavelength nm Idler Figure 2 Relation between Signal and Idler wavelengths 10 GWU Lasertechnik 20 Ul a O linewidth nm typical UI ML red versaScan MB black versaScan BB for versaScan BB HE add 10 degeneracy 709 4 nm pump pulse length straight 4 ns dashed 7 ns 1500 200025
8. screw fig 5 11 to take out this holder gt The compensator fig 5 19 by loosening the screws fig 5 20 gt f present the first signal idler separator mirror by loosening the screw fig 5 22 gt The VIS filter fig 5 18 Install the laser safety beam tube fig 5 5 and the laser safety beam shield fig 5 3 e Direct the pump beam at lowest possible intensity through the centre of the entrance aperture of the versaScan Adjust the legs of the versaScan housing that the pump beam passes through the versaScan and exit through the exit aperture Fix the versaScan to the table Remember that for a versaScan BB HE and for a versaScan MB the OPO should be build up in some distance to the pump laser in order to protect the THG crystal of the pump laser from overlapping outgoing and back reflected 355 nm radiation The distance between the THG crystal of the pump laser and the versaScan output coupler figure 5 9 should be Pulse length of the pump laser in ns x 15 cm This is usually fulfilled for a typical distance between pump laser housing and the versaScan housing of about 30 cm 40 cm e Begin the adjustment of the lens distance with minimum lens distance d and minimum pump energy Slide the inner tube of telescope fig 6 2 to change the lens distance e Increase the lens distance d step by step until the beam diameter in some distance behind the versaScan Is only a little bit bigger then direc
9. signal radiation is polarized vertical like with the BB models while the idler radiation is polarized horizontal This aided already the separation by the standard dichroic signal idler separator mirrors Even when using them near and at degeneracy the reflection of the signal wave of the versaScan MB is still much higher then the reflection of the idler wave even if their wavelengths are the same But a separation quality of better then 500 1 near degeneracy in the wavelength range 620 nm 735 nm is only possible using the polarizing beam splitter cube for the versaScan MB The polarizing beam splitter cube is substituting the first of the 2 dichroic signal idler separators Thus to insert the polarizing beam splitter cube take out the first dichroic signal idler separator by loosening the screw fig 5 22 Put in the beam splitter cube 41 GWU Lasertechnik LIM to the former place of this dichroic signal idler separator mirror Pins in the base plate Ol the VEE Eee AE help to position the polarizing beam splitter cube Conclusion The best possible separation of signal and idler is provided by Wavelenath range Recommended separation optics for versaScan MB 400 nm 620 nm 620 nm 750 nm Polarizing beam splitter cube 50 nm 2630 nm VIS filter with or without dichroic mirrors Tip Above 700 nm between 700 nm and 709 4 nm the reflection of the remaining second dichroic separator may be less then 95 but is
10. take out all optics in the beam path behind the periscope mirrors fig 5 16 These are gt The BBO crystal holder fig 5 14 if the BBO crystal fig 5 12 is mounted therein Be careful not to touch any nearby optics gt The output coupler holder with the output coupler fig 5 9 and the UV filter fig 5 17 therein Loosen the screw fig 5 11 to take out this holder gt The compensator fig 5 19 by loosening the screws fig 5 20 gt If present the first signal idler separator mirror by loosening the screw fig 5 22 gt The VIS filter fig 5 18 If not already done install the laser safety beam tube fig 5 5 Set the pump laser to the lowest output energy possible at 355 nm for the following adjustment l e use long pulse operation mode Make sure that the pump light hits the upper mirror of the periscope in the middle If not adjust the telescope of the versaScan in the way like it is explained in chapter 6 3 At first adjust the parallelism of the beam that exits the versaScan by turning the upper periscope mirror Use a screen to check the position of the beam about 1 m behind the versaScan exit The position of the upper mirror holder is controlled by a pin in the rear panel of the versaScan By loosening the metric screw the upper mirror holder can be turned around the pin and it is possible to adjust the pointing of the beam Laser safety When the metric screw is removed from the rear panel co
11. the beam propagates Prelasing means that there is laser light 1064 nm leaking out of the pump laser BEFORE the Q switch opens You have to detect if there is 1064 nm radiation emitted before the main laser pulse e g using a slow photodiode and an oscilloscope 30 MHz Alternatively the Q switch trigger can be set to external triggering and no trigger signal applied Then it is not allowed that 1064 nm radiation is emitted by the laser detected by a sensitive IR detector card Use black exposed and processed photo paper Put the photo paper always inside a transparent plastic bag to avoid contamination of the optics with ablated dust powder The plastic bags have to be free of any imprints on it e g NO recycling sign imprinted The laser ablation of the imprints will damage optics Direct the laser beam onto the photo paper only one shot at one place DANGER Be very careful with the reflection of the laser beam from the photo paper Protect your eyes Do not look at the photo paper when taking burn pattern 16 GWU Lasertechnik MW e Calculate the energy density of the pump beam Pump energy density mJ cm E355 mJ Fnoriz CM Fer EM 7 with E355 Max output energy of the pump laser at 355 nm in mJ pulse fhoriz lvert Radius horizontal vertical of the 355 nm radiation in cm ni 3 14 If the intense part of the pump beam does not fill the whole beam then calculate the energy density with a mark
12. the crystal by turning the micrometer fig 5 15 or the optional motor to get rid of the crystal reflections which are not of interest 2 or more due to mirror reflections crystal reflections resonator output end mirror coupler crystal HeNe input beam 3 mirror reflections 2 of them overlap when adjustement O K screen coated side with pinhole Figure 9 HeNe reflections from the well aligned versaScan cavity The coated surfaces of the mirrors have to be aligned parallel with respect to each other e Adjust the mirrors in a way that the two reflections from the coated mirror Surfaces are superimposed with the input beam see fig 9 In this case you may notice an interference pattern on the screen around the pinhole e Install the UV filter fig 5 17 to the output coupler holder of the versaScan BB e Turn on the pump laser again and select a reasonable pump energy level 0 45 J cm 0 6 J cm e Tilt the crystal with the micrometer fig 5 15 or if present with the optional motor 32 GWU Lasertechnik ML Now the versaScan BB should oscillate within a certain angle range of the crystal lf not the optical cavity is not aligned properly Repeat the mirror adjustment procedure Once oscillation occurs the versaScan BB will probably require further optimization refer to 7 1 Optimizing the versaScan BB output described below Note It is possible to align the optical cavit
13. the output coupler like described above Then you select a reasonable pump energy level 0 45 J cm 0 6 J cm and adjust the resonator end mirror until the versaScan begins to oscillate Finally fine align the resonator end mirror so that the spot size of the visible OPO output beam is minimized observed on a black screen in a distance of at least 1 m behind the versaScan Note This note is relevant for the versaScan MB only It is not relevant for the versascan BB HE The typical beam shape of the versaScan MB in some distance behind the versaScan MB is elliptical The reason is the minimized divergence of the versascan MB in the horizontal plane typical lt 0 3 mrad The versaScan MB is aligned properly when the beam shape gt 2 m behind the versaScan MB is a vertical narrow line If the line is broadened in the horizontal this broadening means a broadening of the versaScan MB linewidth The versaScan MB is aligned best and has purest narrow linewidth when the stray radiation beyond this line is minimized and the line is as narrow as possible 3 GWU Lasertechnik MW 9 Daily use 9 1 Startup Ensure that the surfaces of the optics are free from dust Particles burned onto the dielectric coatings of the mirrors or the crystal surfaces can lead to reduced output energies Dust particles and pollutants should be removed by blowing clean air onto the surfaces Never blow your wet breath onto the optics Close all the covers of
14. then for relatively short pulses 3 ns 5 ns 9 3 Shut down Just switch off the pump laser Refer to the manual of the pump laser for the shut down procedure We recommend to let the internal cooling water of the pump laser circulate for some minutes after switching off the flashlamp flashing In case of the option M First exit the software ScanMaster and wait for the motor to access its home position Then you can switch off the motor controller 44 GWU Lasertechnik ML 10 Maintenance 10 1 Precautions Do not touch the optical components Wear gloves or use weak plastic tweezers to hold optical components Ensure that the surfaces of the optics are free from dust Particles burned onto the dielectric coatings of the mirrors or the crystal surfaces can lead to reduced output energies Dust particles and pollutants should be removed by blowing clean air onto the surfaces It is recommended to do this any time the versaScan was not in use for more then 1 week or any time the cover of the versaScan was opened Never blow your wet breath onto the optics lf the versaScan will not be in use for a long period of time we recommend to store the BBO crystal in a clean and dry place Preferably use a desiccator for storage From time to time it is recommended to take a burn pattern of the pump laser to observe the laser beam profile Use black exposed and processed photo paper Always place a transparent plastic bag
15. versaScan cavity that the signal and idler waves are collinear e Lower the pump energy density e g by changing the telescope lenses call GWU Note The output power will drop Adjust telescope focal length refer to 6 3 Setup of the telescope Take a pump laser which has longer pulse length pump pulse duration has a strong influence to the versaScan linewidth and divergence Narrow the spectral width of the pump laser i e use an injection seeder Bad beam profile Check the beam profile of the pump laser Check the optics of the versaScan for any evidence of damage Adjust the versaScan cavit Divergence is to high Lower the pump energy density e g by changing the telescope lenses call GWU Note The output power will drop Check pump laser divergence Adjust telescope focal length refer to 6 3 Set up of the telescope Take a pump laser which has longer pulse length pump pulse duration has a strong influence to the versaScan linewidth and divergence idler beam direction changes e Adjust the versaScan cavity that the signal and when changing the idler waves are collinear versaScan wavelength Tuning range is limited e Refer to 6 4 3 Correct the crystal position to obtain the whole tuning range Output energy is not stable e Fine adjust the SHG and THG stage of the pump laser until the generated 355 nm output of the pump laser is maximum Check energy stability of the pump laser Check pump energy It has to
16. 0 1 These lenses have been the standard up to 2010 They are still available as non standard These lens combinations exhibit a bigger change in energy density from step to step compared to the actual standard lens set see chapter 6 3 1 Possible lens combinations On the other hand this lens set covers a much wider range to change the energy density So they may be useful in particular for non standard pump lasers Choose an appropriate set of telescope lenses in order to attain within the target pump energy density 500 mJ cm 550 mJ cm At least try to stay within the recommended pump energy density 500 mJ cm 600 mJ cm Never exceed the allowed pump energy density 450 mJ cm 650 mJ cm Way out Orientate the curvature of the 2 concave lens the other way round then standard But be careful to pre align the lens distance accurately before exposing it with the pump beam 48
17. 00 wavelength nm Figure 3 Typical spectral width of the versaScan 450 400 350 300 250 200 150 1 linewidth cm typical 100 50 red versaScan MB black versaScan BB for versaScan BB HE add 10 degeneracy 709 4 nm pump pulse length straight 4 ns dashed 7 ns 1000 1500 20002500 wavelength nm Figure 4 Typical spectral width of the versaScan 11 GWU Lasertechnik MW 3 1 Electromagnetic compatibility EMC of the option M The GWU OPOs emit very low electromagnetic radio frequency radiation in case of the option M motorised wavelength tuning This statement did not take into account possible emissions by the pump laser The GWU OPOs have been undergoing a comprehensive testing of the EMC according to the FCC regulations that apply in the USA Important In order to maintain the low EMC emissions of the GWU OPOS it is necessary to use only the original connection cables supplied by GWU Follow the instructions in the chapter Option M NOTE This equipment has been tested and found to comply with the limits for 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 equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with this user manual may cause harmful
18. Figure 5 Schematic set up of the versaScan 1 Telescope assembly 13 Crystal rotation stage 2 Screws to the fix telescope 14 Screws to fix the crystal holder 3 Laser safety beam shield dashed 15 Wavelength controlling micrometer 4 Screws to fix laser safety beam shield 16 Pump mirrors refer to chapter 6 4 5 Laser safety beam tube 17 UV filter 17a Set screw UV filter 6 Screw to fix the laser safety beam tube 18 VIS filter 7 Resonator end mirror 19 Compensator 8 End mirror alignment screws 20 Screws to fix the compensator holder 9 Output coupler 21 Dichroic signal idler separators 10 Output coupler alignment screws 22 Screw to fix the signal idler separator 11 Screw to fix the output coupler holder 23 Screw to fix the end mirror holder 12 BBO crystal 24 Screws to fix the periscope 14 GWU Lasertechnik ML 6 Installation 6 1 Install the laser back reflection protection LBP In case of a versaScan BB skip chapter 6 1 and proceed with chapter 6 2 The laser back reflection protection LBP is not needed for the versaScan BB It is necessary for the versaScan BB HE and the versaScan MB which are reflecting back some part of the 355 nm pump beam light The LBP has to be installed inside the pump laser between the SHG and the THG stage If there is no place between the SHG and the THG stage inside the pump laser it is possible to install the LBP in front of the SHG stage where the fundamental 1064 nm radiation of the laser enters the
19. GWU Lasertechnik ML GWU versaScan Beta Barium Borate Optical Parametric Oscillator User Manual V 1 63 Copyright O GWU 03 2012 GWU Lasertechnik 1 LASER SAFETY 1 1 Location of the safety labels 1 1 1 Label types English 1 1 2 Label types German 2 PUMP LASER REQUIREMENTS 3 SPECIFICATIONS OF THE VERSASCAN 3 1 Electromagnetic compatibility EMC of the option M 4 IMPORTANT PRECAUTIONS 5 SCHEMATIC SET UP OF THE VERSASCAN 6 INSTALLATION 6 1 Install the laser back reflection protection LBP 6 1 1 LBP AR coated UV filter 6 1 2 LBP Mirror beam dump 6 2 Characterize the pump beam 6 3 Setup of the telescope 6 3 1 Possible lens combinations 6 3 2 Installation of the lenses 6 3 3 Adjustment of the lens distance 6 4 Adjustable periscope mirrors 6 4 1 Changing periscope mirrors 6 4 2 Adjusting the periscope mirror holders 6 5 Installation of the crystal 6 5 1 Build in the crystal to the crystal holder 6 5 22 Check if the beam is clipped by the crystal 6 5 3 Correct the crystal position to obtain the whole tuning range 6 5 4 Cleaning the crystal 6 6 The compensator crystal 6 6 1 Installation of the compensator crystal 6 7 Option M 6 7 1 Unpacking the Option M 6 7 2 Connecting the Option M ML 12 13 14 15 15 15 15 16 17 17 19 20 22 23 24 26 26 2i 28 28 28 28 29 29 30 GWU Lasertechnik 7 RESONATOR ALIGNMENT OF THE VERSASCAN BB 71 Optimizing the vers
20. UV filter check the pump laser output for any evidence of prelasing Prelasing could damage optics If prelasing occurs tilt the UV filter a little more against the laser beam 6 1 2 LBP Mirror beam dump For pump laser output power of more than 3 6 W at 355 nm e g 200 mJ at 20 Hz 4 W the LBP is consisting of a mirror and a beam dump Place the mirror which Prelasing means that there is laser light 1064 nm leaking out of the pump laser BEFORE the Q switch opens You have to detect if there is 1064 nm radiation emitted before the main laser pulse e g using a slow photodiode and an oscilloscope 30 MHz Alternatively the Q switch trigger can be set to external triggering and no trigger signal applied Then it is not allowed that 1064 nm radiation is emitted by the laser detected by a sensitive IR detector card 15 GWU Lasertechnik ML reflects the 355 nm radiation and transmits 1064 nm and 532 nm radiation under 45 DEG against the laser beam that the back reflection from the OPO is reflected at this mirror under 90 into the beam dump After installing the mirror and the beam dump check if the laser beam passes through the SHG and THG crystal of the pump laser without clipping If the laser beam is clipped position the SHG and THG stage in a way that the laser beam passes through without clipping Adjust SHG and THG angle for maximum 355 nm output power of the pump laser 6 2 Characterize the pump beam Befo
21. aScan BB output 7 1 1 Collinear alignment Overlapping signal and idler beam 7 1 2 Alternative alignment Overlapping signal and pump beam 8 RESONATOR ALIGNMENT OF THE VERSASCAN MB AND THE VERSASCAN BB HE 9 DAILY USE 9 1 Start up 92 Operation 9 2 1 Wavelength tuning 9 2 2 Motorized tuning 9 2 3 Separation of signal and idler 9 2 3 1 VIS filter 9 2 3 2 Dichroic separators 9 2 3 3 Polarizing beam splitter cube 9 2 3 4 Non collinear versaScan alignment 9 2 4 Degeneracy 9 2 4 1 versaScan BB and versaScan BB HE 9 2 4 2 versaScan MB 9 2 5 versaScan beam characteristics 9 3 Shut down 10 MAINTENANCE 10 1 Precautions 10 2 Cleaning optics 11 TROUBLESHOOTING 12 APPENDIX A ML 32 33 34 45 45 45 46 48 GWU Lasertechnik ML 1 Laser safety DANGER Visible AND Invisible Laser Radiation Emission of visible signal wave 398 nm 709 nm and invisible idler wave 710 nm 3300 nm laser radiation as well as pump laser light at 355 nm Exposure to direct or reflected beams can cause severe eye and skin damage Wavelength conversion pumped by class 4 laser product e Avoid looking at the output beam and reflections e Always use protective eyewear e Operate the versaScan at the lowest possible beam intensity allowed by the requirements of the application e Maintain high ambient light level e Avoid unnecessary reflections Use enclosures for beam paths and shields e Let the beam propagate o
22. around the burn pattern photo paper to avoid contamination of the optics with ablated dust powder The plastic bags have to be free of any imprints on it e g NO recycling sign imprinted The laser ablation of the imprints will damage optics Direct the laser beam onto the photo paper only one shot at one place DANGER Be very careful with the reflection of the laser beam from the photo paper Protect your eyes Do not look at the photo paper when taking burn pattern From time to time with most pump lasers it is necessary to fine adjust the SHG and THG crystals This should be done with the pump laser warmed up very well after about 2 hours running time at full power 10 2 Cleaning optics Ensure that the surfaces of the optics are free from dust Particles burned onto the dielectric coatings of the mirrors or the crystal surfaces can lead to reduced output energies Dust particles and pollutants should be removed by blowing clean air onto the surfaces Never blow your wet breath onto the optics If optics cleaning is necessary To clean the BBO crystal surfaces Isopropyl alcohol IPA or a mixture of alcohol and ether in the 1 1 ratio or trichlorethylen or trichlorethan on a soft lens tissue is recommended Never use acetone to clean the BBO crystals The other optics may be cleaned with fresh water free methanol on a soft lens tissue 45 GWU Lasertechnik MW 11 Troubleshooting Spectral width is too large e Adjust the
23. be at least 3 times threshold for stable versaScan operation But the pump energy density behind the telescope must not exceed 0 65 J cm for pump pulse duration gt 4 ns or 0 6 J cm for pump pulse duration lt 4 ns Adjust the versaScan cavity Check the optics of the versaScan for any evidence of damage 46 GWU Lasertechnik ML Output energy is too low Fine adjust the SHG and THG stage of the pump laser until the generated 355 nm output of the pump laser is maximum Check pump energy It has to be at least 3 times threshold for stable versaScan operation But the pump energy density behind the telescope must not exceed 0 65 J cm for pump pulse duration gt 4 ns or 0 6 J cm for pump pulse duration lt 4 ns Adjust the versaScan cavity Check the optics of the versaScan for any evidence of damage versascan does not oscillate Check polarization of the pump laser 355 nm It no versaScan output has to be horizontal Check the optics of your versaScan for any evidence of damage Check pump energy The pump energy density behind the telescope has to be higher than 0 45 J cm in a beam diameter bigger than 3 mm Repeat the whole versaScan installation and adjustment procedure In the case that you have problems with your GWU OPO call our service engineers Headquarter Technical Support GW U Lasertechnik GmbH GWU Lasertechnik GmbH Bonner Ring 9 Kohlenhofstrasse 10 50374 Erftstadt Lechenich 67663 Kaiserslautern Germa
24. cal shock Do not use this transportation container to store the crystal It is appropriate only for the short storage of during the transport After the delivery take out the crystal and place the crystal in a clean and dry place Preferably use a desiccator for storage Avoid focussed back reflection of the OPO output into the OPO It could possibly damage optical components The alignment of the telescope of the versaScan should only be done by authorized service engineers They have to be extremely careful that the pump beam exits the telescope with minimum divergence and does not exhibit a focus There is no need to readjust the telescope after initial installation unless the pump laser beam parameters has been changed The versaScan resonator should not be exposed to pump energy densities of more than 0 65 J cm for a pump pulse duration gt 4 ns and 0 6 J cm for a pump pulse duration between 2 5 ns and 4 ns 13 GWU Lasertechnik ML 5 Schematic set up of the versaScan Pr mo I Beam shield Pains ii only with motor EFH OR 355 nm w t OPO out Q 405 nm 2 55 um To a 60 5 cO N Motor dn H optional N a Eas aay it 7 2 919 2 a a om A mJ mJ o S Feet elongations available as 8 23 24 4 14 11 10 22 21 Motorposiionfo f o 1 i N t Da ETT gg a 405 nm 709 nm 2 st Pump in 355 nm Idler out 710 nm 2 55 um
25. ch screw that this sidewards tail goes on average exactly sidewards not sidewards up and not sidewards down It may be that the upper part of the tail goes a little bit upwards and the lower part of the tail goes a little bit downwards Align the upper fine pitch screw in a way that the middle part of the tail points exactly sidewards Then align the lower fine pitch screw to achieve the minimum horizontal beam diameter observed on the black screen in gt 1 m distance behind the OPO Now the versaScan MB or versaScan BB HE is aligned properly with a collinear alignment This means the pump the signal and the idler radiation are collinear There is no need to perform a procedure like in chapter 7 1 Optimizing the The upper fine pitch screw of the resonator end mirror is the fine pitch screw behind the laser safety beam tube fig 5 5 36 GWU Lasertechnik ML versaScan BB output since the alignment of the back reflection of the output coupler ensures the collinear alignment If you want you can double check the collinear alignment of the versaScan like described in chapter 7 1 But note for the versascan MB that the birefringence of the BBO crystal leads to a beam walk off of the signal beam against the idler beam Thus for the versaScan MB you should ae BASO that loke LII wave canc tne aE wave are collinear atlas ae Sao Note It is possible to align the optical cavity without using a HeNe laser In this case first you adjust
26. d the versaScan BB and mark the pump beam spot on a screen in a distance of at least 1 m behind the versaScan BB e Now raise the pump power until the versaScan BB oscillates with low output power lt 5 mJ pUlse e First adjust both versaScan BB resonator mirrors that the signal beam approaches the pump beam mark on the screen until the signal beam is at this mark e Then fine adjust only one mirror input mirror or output coupler until the size of the visible signal spot is minimized observed on the screen e Finally observe the signal beam direction again Repeat the adjustment procedure above until the signal points towards the mark on the screen and its spot size is minimized 34 GWU Lasertechnik ZAVA 8 Resonator alignment of the versaScan MB and the versaScan BB HE Recommended equipment HeNe Laser beam steering optics for HeNe The versaScan has to be set up with all optics built in except the UV filter fig 5 17 by loosening the set screw figure 5 17a and the VIS filter fig 5 18 and the compensator fig 5 19 and the first dichroic signal idler separator mirror fig 5 22 or the alternative polarizing beam splitter cube have to be removed e Use a pin to pierce a pinhole in a sheet of black photo paper Place and fix the photo paper between the pump laser and the versaScan with the black side towards the pump laser and the white side towards the versaScan If you do not have such photo paper i
27. ed and the screws are fixed when it is delivered to the customer No readjustment is needed during normal operation and after the versaScan once is installed Although when changing periscope mirrors the mirror holders must be adjusted The procedure for changing periscope mirrors is explained in chapter 6 4 1 The adjustment of the periscope is explained in chapter 6 4 2 Laser safety When opening the cover e g for alignment ensure that the laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 is in place any time pump laser light is entering the versaScan Otherwise harmful reflections from the tilted BBO crystal will put the user at high risk safety panel lower mirror holder Figure 7 a Adjustable periscope mirror holders front view 22 GWU Lasertechnik MA ll NU 6 4 1 Changing periscope mirrors To change the periscope mirrors first remove the laser safety beam shield fig 5 3 Then loosen and screw out completely the metric screws M4 wrench size 3 that attach the periscope mirror holders to the rear panel of the versaScan On each of the screws two washers and one lock washer are mounted These washers are needed on the one hand to make the mirror holders adjustable and on the other hand to fix them securely to the rear panel For the correct arrangement of the washers refer to figure 7 b The stack of washers consists of two normal washers with one lock washer between Af
28. ed down beam radius between the radius of the whole beam and the radius of the intense part The versaScan shall be pumped at 355 nm with the recommended pump energy density 500 mJ cm 600 mJ cm If the energy density of the 355 nm pump beam is different the energy density has to be changed by using an appropriate set of telescope lenses inside the versaScan telescope assembly The allowed range is between Allowed pump energy density 450 mJ cm 650 mJ cm 6 3 Setup of the telescope The telescope is a Galilean type consisting of a plano convex and plano concave lens see fig 6 below Ask your GWU OPO service support for the correct telescope lenses appropriate to your pump laser Only authorized service engineers should do the versaScan telescope setup and alignment They have to be extremely careful that the pump beam exits the telescope with minimum divergence and does not exhibit a focus and they have to double check that the correct pump energy density for the versaScan is obtained The pump energy density must not exceed 0 65 J cm but should be higher than 0 45 J cm to obtain high conversion efficiency To perform the telescope alignment most optics has to be removed from the versascan 6 3 1 Possible lens combinations If the energy density of the pump beam is different the required energy density for the versaScan could be obtained by using one of the lens combinations in the following table 1 and table 2 see as
29. ehind the BBO crystal behind the versaScan housing If you see any clipping on top or bottom of the burn pattern adjust the height of the lower mirror holder again Now the adjustable periscope mirror holders are installed and adjusted correctly and should not be touched anymore during the following installation procedure 25 GWU Lasertechnik MW 6 5 Installation of the crystal Markings on the upper side of the crystal Set screw Pressure plate Crystal TAI VOI Glass interfaces ODO OK gt SOR Oe eee QOL DO A xx XK KOK XX Screws to fix l l crystal holder to sectional view Crystal holder rotation stage Figure 8 The crystal holder of the versaScan 6 5 1 Build in the crystal to the crystal holder First take out the crystal holder out of the versaScan Remove the laser safety beam shield fig 5 3 above the crystal rotation stage fig 5 13 by loosening the 2 screws fig 5 4 Then loosen the 2 metric M3 screws fig 5 14 fixing the crystal holder to the rotation stage and take out the crystal holder Be careful not to touch any nearby optics The BBO crystal is packed in a small plastic transparent transportation container This container protects the crystal from mechanical shock during transport 26 GWU Lasertechnik MM Note Do not use the transportation container to store the crystal It is appropriate only for the short storage during the transport Place the crystal in a clean
30. ensity is typically just at the reaction threshold of the burn pattern photo paper Thus sometimes the photo paper does not react on it Or it reacts only at the intense parts of the signal radiation which are then just above the reaction 43 GWU Lasertechnik ML threshold of the photo paper forming a strange looking burn pattern because most of the beam is not comprised therein We recommend to use a camera instead to analyze the real characteristic of the full versaScan output beam The versaScan BB beam is round and flat top with a very smooth energy distribution Only for pump lasers with a very unbalanced energy distribution in the beam this structure of the pump laser may be visible as well in the OPO beam Structures in the pump beam which are smaller than 1 mm are flattened completely by the OPO In a bigger distance behind the OPO the versaScan MB beams signal and idler are forming vertical lines because of their bigger divergence angle in the vertical plane The versaScan MB beam shape is flat top as well but may contain some typical structure like few 1 vertical and 2 3 horizontal narrow lines with low intensity In most cases this structure is only faint depending on the pump laser But this structure will occur and is typically strong when using a seeded narrow linewidth pump laser The versaScan divergence angles scale with the pump pulse duration For relatively long pulses 7 ns 10 ns the OPO divergence is much less
31. filter but it is still very harmful invisible CLASS 4 laser radiation Use laser safety goggles against this invisible IR radiation 680 nm 3000 nm 9 2 3 2 Dichroic separators Dichroic signal idler separator mirrors are available as an option A set consists of two mirrors fig 5 21 which are reflecting the signal wave 405 nm 709 nm under 45 and transmitting the idler wave 710 nm 2630 nm 40 GWU Lasertechnik To insert dichroic signal idler separator mirrors put the mirror holders to the pins and fix them with the setscrew fig 5 22 lt is recommended to put the VIS filter fig 5 18 into the idler branch to clean up the transmitted idler beam from remaining signal radiation Be aware that the transmission of the VIS filter in the wavelength range 710 nm 740 nm varies between only 28 at 710 nm up to 87 at 740 nm The transmission of the VIS filter is higher than 90 at 750 nm 2200 nm Separation quality of this set up idler wave Better then 10000 1 between 735 nm and 2630 nm behind VIS filter signal wave versaScan BB and versaScan BB HE Better then 300 1 between 405 nm and 620 nm versaScan MB Better then 500 1 between 405 nm and 620 nm 9 2 3 3 Polarizing beam splitter cube Available as an option only for the midband OPO versaScan MB operable only in the wavelength range 600 nm 870 nm For the versaScan MB the signal and idler radiation is polarized different The
32. hanges typically by about 1 time the versaScan line width The actual versaScan line width is mostly depending on the actual versaScan wavelength see fig 3 and fig 4 By experience the pointing direction of the pump laser changes slowly by time in particular when warming up This means there is no shot to shot wavelength change but a slow drift during hours of operation may occur Up to now we know only one extremely compact pump laser specified pointing stability 200 urad where a shot to shot wavelength jitter of the OPO has been observed The wavelength drift due to temperature change of the BBO crystal is negligible since the temperature tuning of BBO is extremely low A temperature change of 15 to 25 C will lead to a wavelength drift of only 1 time the linewidth of the versaScan If such a big room temperature change will occur the wavelength change due to other effects which affect mainly the beam directions mechanical laser pointing will be bigger Only during the first 5 minutes the pump light is entering the versaScan the wavelength may drift a little bit due to warming up the crystal This effect is nearly not noticeable for low power 10 Hz systems and may score up to approximately 1 time the linewidth all for systems with high pump power and or high repetition rates gt 10 Hz 9 2 2 Motorized tuning For the GWU versaScan and the GWU premiScan automated wavelength tuning is available Option M If the motorized tu
33. lder and fix it gently with the set screw in the middle of the top side of the compensator holder e Install the compensator holder to its rotation stage 28 GWU Lasertechnik 7 6 7 Option M The Option M is a motorization add on for the versaScan and the optional uvScan to automate the wavelength tuning 6 7 1 Unpacking the Option M The Option M for the versaScan consists of 1pc controller box 1pc mains lead 1pc RS232 cable 1pc SubD 15 cable 1pc software CD optional 1pc SubD 25 cable if the controller supports a uvScan The DC Motor s is are already mounted in your device s if the Option M is ordered 29 GWU Lasertechnik ML 6 7 2 Connecting the Option M The terminal board is equipped with the following connectors Digital IO Motor out RS 232 in for remote to from PC control versaScan Connect a COM Port of your PC to the connector RS 232 IN with the provided null modem cable Use the 15 pin Sub D cable to connect the OPO with the controller The Digital I O Port can be used for optional remote control of the OPO unit Please refer to the software manual for further information about remote control options If the optional uvScan is present as well connect the OUT terminal of the uvScan controller panel with the uvScan using the provided IEEE 25 pin Sub D cable 30 GWU Lasertechnik The backside of the controller box The controller box is operated with
34. mains power 100 240VAC 50 60 Hz Connect the IEC C14 socket with a IEC C13 line plug and a appropriate wall plug for your country on the other end There is a fuse carrier equipped with two 1 6A slow blow fuses 5x20mm 11 6A 250V AC integrated into the IEC C14 socket As well the mains switch is mounted above the socket 31 GWU Lasertechnik MW 7 Resonator alignment of the versaScan BB Recommended equipment HeNe Laser beam steering optics for HeNe The versaScan BB has to be set up with all optics built in except the UV filter fig 5 17 by loosening the set screw figure 5 17a and the VIS filter fig 5 18 and the compensator fig 5 19 and the first dichroic signal idler separator mirror fig 5 22 have to be removed Laser safety The laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 must be in place Harmful reflections from the tilted BBO crystal will otherwise put the user at high risk e Turn off the pump laser or block the pump beam e Direct the HeNe beam from the exit side through the versaScan BB in the opposite direction to the pump beam e Puta paper screen with a small hole between HeNe and versaScan BB e Observe the back reflections from the resonator mirror surfaces see fig 9 Note The output coupler is wedged You will see 2 reflections from the output coupler The stronger reflection is the one from the coated surface when using a visible alignment laser Tilt
35. mp wavelength 42 GWU Lasertechnik ML 9 2 4 1 versaScan BB and versaScan BB HE For the versaScan BB and the versaScan BB HE it is not possible anymore to separate signal and idler at and near degeneracy since they can no more be distinguished They are degenerated As well the different wavelengths separations described above under 8 2 2 do not work properly near degeneracy between about 690 nm and 730 nm The versaScan BB HE beam characteristics like the divergence described above in 8 2 3 and the spectral behaviour are changing as well near degeneracy The linewidth of the broadband OPO versaScan BB HE is maximal at degeneracy reaching about 8 nm to 20 nm mostly depending on pump pulse length But the versaScan BB HE output energy is typically about maximum at degeneracy The degeneracy gap 690 nm 730 nm does not mean that the versaScan is not operating at degeneracy It means that the typical beam characteristic is changing and that it is no more possible to separate signal and idler making the output useless for many applications 9 2 4 2 versaScan MB With the midband OPO versaScan MB it is possible to separate signal and idler at degeneracy since they differ by polarization As well the linewidth of the versaScan MB is constant with about 4 cm for 7 ns pump pulse length over the whole tuning range except near degeneracy where it may rise by 50 Only few optics need to be changed to upgrade the versaScan BB o
36. mpletely the upper mirror holder can be turned around the pin completely Harmful reflections from the tilted mirror holder will put the user at high risk when it is turned to the wrong side and the beam can exit the versaScan to the top The combination of the screw with two washers and one lock washer between makes it possible to turn the upper mirror holder a bit with some friction to the rear panel Adjust the friction by loosening the metric screw a little bit By turning the upper mirror holder it is possible to adjust the parallelism of the beam relative to the table When the beam is parallel to the table hold the upper mirror holder with one hand l e press the holder with your thumb to the rear panel of the versaScan and with the other hand use a metric Allen key wrench size 3 to tighten the screw 24 GWU Lasertechnik ML Important While tightening the screw check that the position of the beam on the screen does not move Now the upper mirror holder is positioned correctly and must not be touched anymore during the further installation process The beam height through the BBO crystal is adjusted with the lower periscope mirror holder The lower mirror holder is guided by two pins on the rear panel and one metric screw refer to figure 7 b Do not screw out the metric screw completely as the lower mirror holder will not stay on the rear panel on its own The combination of metric screw and washers is the same as with the uppe
37. ning is installed it is still possible to change the wavelength of the versaScan with the micrometer fig 5 15 as well As a further option a lambdameter lambdaScan can be added which integrates within our user friendly software The lambdaScan is providing convenient absolute wavelength control and full automated OPO wavelength calibration Be aware that the full wavelength range for the motorized tuning is available only if the micrometer fig 5 15 is screwed out completely 26 mm on scale Which are defining the signal beam direction 39 GWU Lasertechnik ML Vice versa the wavelength range can be accessed by the micrometer only if the motor is moved out completely In the Scanmaster software click the button Out in Manual Control to move out the motor The versaScan mechanic is allowing 2 different positions to attach the motor leading to different crystal tuning angle ranges The full angle range of the crystal rotation stage is accessible by the motor if the motor is placed in the position signed for the versaScan MB in figure 5 In the position signed for the versaScan BB the motorized angle range is somewhat smaller The default motor position for the versaScan BB is allowing the full wavelength tuning range for the versaScan BB and the versaScan BB HE If you place the motor in the default position for the versaScan MB the OPO can do a higher maximum tuning speed but the wavelength repeatability acc
38. nly in a restricted area in a horizontal plane which is not at the typical height of the eyes e Do not move your head eyes down to the height of the beam path e he laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 have to be fixed in place any time the pump laser light is entering the versaScan Otherwise harmful reflections from the tilted BBO crystal will put the user at high risk 1 1 Location of the safety labels The following safety labels are used throughout the versaScan Refer to diagrams A amp B for their location The labels must not be removed or defaced Immediately replace any missing labels Label types are shown in 1 1 1 and 1 1 2 The laser safety officer must add replace the safety labels with labels in the language typical for the country corresponding to the regional laser safety regulations 4 GWU Lasertechnik ML Label location diagram A GWU Lasertechnik ML Top amp front panels of the versaScan Label location diagram B GWU Lasertechnik 1 1 1 Label types English Label 1 Part no 902108 A Label 3 Part no 902100 VISIBLE prepo Nj AVOID EYE OR oan EXPOSURE DIRECT OR SCATTERED RADIA POWER W app AND PULSE WIDTH DEPEND ON OPTIONS AND LASER CONFIG URATION CLASS IV LASER PRODUCT Label 5 Part no 902101 Label 2 Part no 902104 Label 4 Part no 902102 Label 6 Part no 902105 ML GWU Lasertechnik 1 1
39. ny Germany Phone 49 2235 9 55 22 0 49 631 303 88 99 FAX 49 2235 9 55 22 99 49 631 303 88 76 E mail info gqwu group de info gwu group de It is our job to make you satisfied Copyright GWU 03 2012 The OPO threshold is the pump energy at which the OPO begins to oscillate To measure the threshold attenuate your pump laser until the OPO emission is barely visible Measure the pump pulse energy at this point threshold 47 GWU Lasertechnik Wl 12 Appendix A Lens combinations used as standard up to 2010 Table 3 Magnification of the pump beam diameter lowering the energy densit Diameter Energy density Focal length Lens Comment magnification lowered down to mm distance factor Jai 1 1167 0735 150 175 Standard telescope Standard telescope 1 133 0565 75 100 e 1 15 0444 100 150 o 1 1 167 0358 75 1235 50 1 175 08327 100 1735 12 0255 75 150 FH 1 233 0184 75 1735 10 MM 21 Table 4 Reduction of the pump beam diameter rising the energy densit Diameter Energy density Focal length Lens Comment reduction rises by factor mm distance a Toe e mm 175 f 175 150 ao 141 1 0 10 1 0 5 4 0 150 75 15 self destroying the focus from the beam reflected by the plane surface of the 2 concave lens is inside the 1 convex lens 1 0429 543 175 75 1
40. r versaScan BB HE to the versaScan MB 9 2 5 versaScan beam characteristics The signal beam is emitted divergent while most energy of the idler beam is emitted convergent forming a beam waist with about 1 mm diameter about 20 cm to 40 cm behind the versaScan In case of the midband OPO versaScan MB this behaviour takes only place in the vertical plane This means that for the versaScan MB the signal wave is divergent and the idler wave is convergent only in the vertical axis while the signal and idler divergence is minimized in the horizontal see chapter 3 Specifications of the versaScan This means that the idler beam waist for the versaScan MB is forming a horizontal line instead of a round spot for the versaScan BB or the versaScan BB HE about 20 cm to 40 cm behind the OPO Be careful when placing optics near the beam waist of the versaScan Many optics like mirrors with a metallic coating Al Ag Au may be damaged near the idler beam waist Other even coated optics for high power applications prisms lenses dichroic mirrors are usually not damaged The idler beam waist can be observed by taking burn patterns behind the versaScan lf you let the signal beam exit collinear together with the idler wave then a weak burn pattern of the signal beam may be discovered around this beam waist as well For the ideal collinear alignment of the versaScan the idler beam waist should be in the centre of the signal beam The signal energy d
41. r mirror holder Loosening the screw a little bit to adjust the friction to move the mirror holder in vertical direction The total range of vertical movement is 3 mm Install the BBO crystal into the versaScan Refer to chapter 6 5 to install the crystal Laser safety High risk Be very careful that the BBO crystal is NOT tilited against the pump beam Otherwise harmful invisible pump light reflections from the tilted BBO crystal set the user to high risk of eye damage because the laser safety beam shield fig 5 3 is not in place Use protective eyeware against the 355 nm pump radiation and execute the following adjustment with lowest possible energy out of the pump laser Watch the blue florescence of the pump beam on a white paper behind the crystal holder to adjust the beam height through the middle of the BBO crystal You can use a transparent lens tissue in front of the versaScan as well in order to make the BBO crystal visible on the white paper Once it is adjusted keep the position of the lower mirror holder with one hand i e press the holder with your thumb to the rear panel of the versaScan and with the other hand use a metric Allen key wrench size 3 to tighten the screw While tightening the screw check that the position of the beam on the screen does not move Now fix the laser safety beam shield fig 5 3 and place a beam dump behind the versaScan and set the laser to the full power used for OPO pumping Take burn pattern b
42. re installing the versaScan the pump beam characteristic has to be checked e Check the pump laser output for any evidence of prelasing Prelasing can damage optics e Check the polarization of the pump laser at 355 nm It needs to be horizontal e Allow the pump laser about half an hour to warm up at full power e Optimize the pump laser output at 355 nm Fine adjust the SHG and THG crystal angles If present align the polarization rotator A 2 waveplate in front of these HG stages for max 355 nm output as well If possible check if the Q switch delay parameter of the pump laser control electronic is optimized for max laser output e Once it is optimized measure the maximum possible output energy of the pump laser at 355 nm E355 e Take burn patterns in different distances behind the laser Inspect the burn patterns for any evidence of hot spots inside the pump beam Hot spots could damage the OPO optics The pump beam does not need to be round even though this is mostly preferred but the intense part of the beam should form one continuous closed area The bigger this area is the better A flat top beam profile is mostly preferred for pumping the GWU OPOs e Determine the beam diameter and divergence of the pump beam using the burn patterns Useful are magnifying glasses and or a calliper rule The beam divergence of the pump beam should be less then 0 5 mrad This means the beam diameter should rise less then 0 5 mm for every 1 m
43. slide out the inner tube fig 6 2 completely e Fix the lenses in the telescope housing with the curved side of the lenses orientated as shown in fig 6 o Slide i in a the it inner rua again Be aware gt that there are s two possibilities depending on which end you slide in first resulting in a large change of lens distance e Install the laser safety beam tube fig 5 5 reduction magnification of the pump beam diameter of the pump beam diameter f gt 0 f lt 0 f lt 0 f gt 0 C 1 d f f E i E zi Do 5 3 7 for short lens distance pez 113 Figure 6 Set up of the telescope 1 Telescope housing 6 Setscrew for lens holder 2 Telescope housing inner tube 7 Use a long screw M3 to 3 laser safety beam tube access slide the inner tube 2 4 1 lens 8 Setscrew for lens distance 5 p lens 9 Setscrew for telescope housing GWU Lasertechnik MM 6 3 3 Adjustment of the lens distance The telescope lens distance has to be aligned for minimum divergence of the pump beam behind the telescope e First take out of the versaScan all optics in the beam path behind the pump mirrors in the periscope fig 5 16 These are gt The BBO crystal holder fig 5 14 if the BBO crystal fig 5 12 is mounted therein Be careful not to touch any nearby optics gt The output coupler holder with the output coupler fig 5 9 and the UV filter fig 5 17 therein Loosen the
44. st be in place Harmful reflections from the tilted BBO crystal will otherwise put the user at high risk Be aware that the full angle tuning range of the crystal is possible for the motor only if the micrometer is screwed out completely 26 mm on scale Vice versa the full angle tuning range can be accessed by the micrometer only if the motor is moved out completely In the Scanmaster software click the button Out in Manual Control to move out the motor Only for versaScan BB and versaScan BB HE Be aware that it is possible to tit the crystal much more than needed that the beam will be clipped for extreme tilt angles For this test it is sufficient to tilt the crystal between 7 mm and 18 mm on the scale of the micrometer screw or between 1 300 000 counts and 1 300 000 counts with the motor e lf the beam is clipped reposition the whole versaScan housing by adjusting the legs A small re adjustment can be done by loosening the three screws fig 5 2 of the telescope and adjust the position of the telescope 2 GWU Lasertechnik ML 6 5 3 Correct the crystal position to obtain the whole tuning range The typical tuning range is 410 nm gt 2630 nm If the tuning range is shifted it is necessary to tilt the crystal a little bit inside its holder In order to do this remove the crystal holder out of the versaScan and tilt the crystal with soft plastic tweezers inside the holder Do not use force to tilt the cr
45. t behind the telescope A white piece of paper can be used to watch the beam diameter at lowest pump energy 20 GWU Lasertechnik MM e Once the divergence is pre aligned place a beam stop in some distance behind the versaScan and set the pump energy to full power Fine align the lens distance by taking burn patterns behind the telescope and in some distance about 1 m behind the versaScan The lens distance is optimized when the divergence of the pump beam behind the telescope is minimized This is the case when the beam diameter 1 m behind the versaScan is about 0 5 mm bigger then direct behind the telescope lf the horizontal pump beam divergence is different from the vertical elliptical beam then try to minimize the horizontal divergence But do not allow the vertical to focus e Fix the lens position with the setscrew fig 6 8 e Check again the beam diameter and intensity 0 65 J cm recommended 0 5 J cm 0 6 J cm e Once the telescope is aligned first build in the BBO crystal to the versaScan and check if the pump beam is clipped by the crystal see below Then build in the other optics 21 GWU Lasertechnik ML 6 4 Adjustable periscope mirrors Figure 7 a shows a drawing of the adjustable periscope mirror holders in the versaScan The mirror holders are shown in red while the other paris of the versaScan are shown in grey The periscope of the versaScan is already adjust
46. t is possible to use a business card or some thick paper which prevents the pump laser beam from shining through e Turn on the pump laser and attenuate it until the 355 nm pump beam is just visible on a white business card e Arrange the photo paper screen that the pinhole is in the middle of the pump beam e Observe the back reflections from the versaScan at the photo paper screen Adjust the output coupler fig 5 9 until its back reflection is collinear with the input beam and runs back through the little hole in the paper screen e Turn off the pump laser or block the pump beam 35 GWU Lasertechnik ML Now align the resonator end mirror fig 5 7 only e Turn off the pump laser or block the pump beam e Direct the HeNe beam from the exit side through the versaScan in the opposite direction to the pump beam e Put the photo paper screen with the pinhole between HeNe and versaScan with the white side towards the versaScan e Observe the back reflections from the resonator mirror surfaces see fig 9 Note The output coupler is wedged You will see 2 reflections from the output coupler The stronger reflection is the one from the coated surface when using a visible alignment laser Tilt the crystal by turning the micrometer fig 5 15 or the optional motor to get rid of the crystal reflections which are not of interest e Adjust only the resonator end mirror fig 5 7 that its reflection is superimposed with the s
47. ter removing the metric screws the mirror holders can be removed by pulling them out to the front of the versaScan perpendicular to the rear panel Both mirror holders are set on pins so be careful when pulling them out of the system Next remove the small safety panel on the top of the upper mirror holder refer to figure 7 a Use the small setscrews on the side of each mirror holder to remove the upper and the lower mirror and replace them by new ones Put in the new mirror with the coated side facing down The coated side is marked on the side of the mirror with a small gt shaped sign The tip of this sign points towards the coated side On both mirror holders there are small edges on the opposite side of the setscrews which hold the mirrors safely in their position Make sure that both mirrors are resting on these edges after assembly washer lock washer washer metric screw wrench size 3 Figure 7 b Adjustable periscope mirror holders rear view 23 GWU Lasertechnik ML Afterwards clip the mirror holders on the pins again and put in the setscrews with the washers in the rear panel You do not have to assemble the metric screws completely as the holders need further adjustment The procedure for the adjustment is explained in chapter 6 4 2 Due to safety reasons attach the small safety panel on the upper holder again before adjusting the upper mirror holder 6 4 2 Adjusting the periscope mirror holders lf not already done
48. the versaScan before switching on the pump laser If the covers are partially open Laser safety Ensure that the laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 is in place any time pump laser light is entering the versaScan Harmful reflections from the tilted BBO crystal will otherwise put the user at high risk Refer to the manual of the pump laser for the start up procedure of the pump laser We recommend to allow the pump laser to warm up first typically 15 min with the flashlamps at full power Typically the first shots of the pump laser are hotter than usual if you open an intracavity shutter of the pump laser or if you switch it to Q switch operation with full flashlamps power We recommend NOT to use these first shots for the versaScan Reduce the flashlamps drive a little bit before opening the shutter or switching the laser into Q switch operation Then rise the flashlamps power again Or block these first shots in front of the versaScan 9 2 Operation lf the versaScan output stability or energy is poor we recommend to fine adjust the phasematching angles of the SHG and THG crystals of the pump laser at first to reach the maximum 355 nm output The final fine adjustment of these SHG and THG stages should be done after the pump laser has warmed up well with the pump laser light going through the SHG and THG stages for more then 1 hour at full power 9 2 1 Wavelength tuning Use the micrometer fig
49. tor card and the filter e Remove the VIS filter e First adjust the signal beam towards the idler beam by adjusting both mirrors around the horizontal or the vertical axis e Then fine adjust only one mirror input mirror or output coupler until the size of the visible signal spot is minimized This can be observed best about 2 m behind the versaScan BB e Finally observe the idler beam direction again Repeat the adjustment procedure above until the signal and the idler radiation are collinear 33 GWU Lasertechnik ML 7 1 2 Alternative alignment Overlapping signal and pump beam If there is no IR sensitive detector card available it is alternatively possible to overlap the signal and the pump beam behind the OPO However the above described method to overlap signal and idler is more accurate since the birefringence of the BBO crystal leads to a beam walk off of the pump beam against the signal and idler beams resulting in a horizontal side wards displacement of the pump beam against signal and idler of about 1 mm e To overlap the signal and the pump beam the filters fig 5 17 and fig 5 18 have to be removed from the versaScan Loosen the set screw figure 5 17a to take out the UV filter e Take out the first dichroic signal idler separator mirror by loosening the screw figure 5 22 as well e Attenuate the pump laser until the pump beam is just visible on a white business card e Observe the pump beam direction behin
50. trong reflection of the coated surface of the output coupler In this case you may notice an interference pattern on the screen around the pinhole e Putin the UV filter fig 5 17 to the output coupler holder of the versaScan e Turn on the pump laser again and select a reasonable pump energy level 0 45 J cm 0 6 J cm Now the versaScan should oscillate If not adjust the reflection of the resonator end mirror a little bit besides the reflection of the output coupler that the reflection of the output coupler is between the pinhole and the reflection of the resonator end mirror In case of a versaScan BB HE tilt the BBO crystal as well with the micrometer fig 5 15 or if present with the optional motor e Finally fine align the resonator end mirror so that the spot size of the visible OPO output beam is minimized observed on a black screen in a distance of at least 1 m behind the versaScan e Only for the versaScan MB to ease the final fine alignment of the upper fine pitch screw of the resonator end mirror which tilts the mirror around the horizontal axis leads to a vertical beam displacement The lower fine pitch screw is much more sensitive and it is much easier to recognize the best alignment of this screw Thus it is recommended first to tilt misalign the lower fine pitch screw a bit that a sidewards tail is visible in the OPO beam observed on the black screen in gt 1 m distance behind the OPO Then align the upper fine pit
51. uracy is poorer In case of a versaScan MB only the default position of the versaScan MB is providing the full wavelength tuning range for the versaScan MB The wavelength accuracy of the versaScan MB can be improved by placing the motor to the default position of the versaScan BB but then the versaScan MB tuning range is limited narrowed 9 2 3 Separation of signal and idler The versaScan is generating two different wavelengths The signal wave and the idler wave In other words the versaScan Is splitting single pump photons into two photons The photons with the higher photon energy are forming the signal wave 405 nm 709 4 nm and the photons with the lower photon energy are forming the idler wave 709 5 nm 2550 nm Both waves are emitted from the versaScan simultaneously through the same exit aperture In order to separate signal and idler there are the following possibilities 9 2 3 1 VIS filter The VIS filter 25 mm x 3 mm black colour is delivered together with the versaScan The VIS filter is absorbing the visible signal beam in the range 405 nm to 690 nm allowing to use pure idler radiation in the IR range 730 nm to 2630 nm The VIS filter can be mounted to the exit aperture of the versaScan fig 5 18 Separation quality The VIS filter is suppressing the signal wave better then 10000 1 for the idler wavelength range 735 nm to 2630 nm Laser safety Take care The versaScan output is no more visible behind the VIS
52. well Appendix A for non standard lens combinations and for systems built prior to 2011 Choose an appropriate set of telescope lenses in order to attain within the target pump energy density 500 mJ cm 550 mJ cm At least try to stay within the recommended pump energy density 500 mJ cm2 600 mJ cm Never exceed the allowed pump energy density 450 mJ cm 650 mJ cm 17 GWU Lasertechnik Table 1 Maqnifi Diameter Energy density Focal length Lens Typical for Quanta Ray lasers magnification lowered down distance if OPO crystal height is mm to factor mm 1 1 1 1 1 43 l 1 143 175 250 75 20 70 609 1 235 8 40 16 1014 250 10 Diameter Energy density Focal length Lens Typical for Quanta Ray lasers reduction rises by factor mm distance if OPO crystal height is mm mm 1 0 0 1 0 795 1 0 0 745 1 0 638 Take into account that the beam diameter has to be smaller than the aperture of the OPO crystal as well It is possible that you have to reduce and limit the pump power of the laser to be able to stay below 600 mJ cm in the energy density and to be smaller with the beam diameter then the OPO crystal O 0 682 O 18 GWU Lasertechnik 7 6 3 2 Installation of the lenses e Take off the laser safety beam tube fig 5 5 amp fig 6 3 by loosening the screw fig 5 6 e Loosen the setscrew fig 6 8 and
53. y without using a HeNe laser In this case you select a reasonable pump energy level 0 45 J cm 0 6 J cm and adjust only one of the two resonator mirrors until the versaScan BB begins to oscillate However this method can possibly require some patience and it is strongly recommended to carry out the procedure Optimising the versaScan BB output afterwards 7 1 Optimizing the versaScan BB output Required equipment Protective eyewear against the invisible idler radiation 710 nm 3000 nm IR sensitive detector card To optimize the versaScan BB output the optical cavity needs a final precise alignment by means of adjustment of the resonator mirrors Laser safety The laser safety beam shield fig 5 3 and the laser safety beam tube fig 5 5 must be in place Harmful reflections from the tilted BBO crystal will otherwise put the user at high risk 7 1 1 Collinear alignment Overlapping signal and idler beam e First the signal idler separation optics have to be removed from the versaScan Take out the VIS filter fig 5 18 and the first dichroic signal idler separator mirror by loosening the screw figure 5 22 e Attenuate the pump until the versaScan BB oscillates with only low output power lt 5 mJ pulse e Put the VIS filter in the versaScan BB output beam e Use the IR sensitive card to check the idler beam direction behind the OPO DANGER Be careful with the reflection of invisible radiation from the detec
54. ystal inside the holder If you need force tighten the setscrew fig 8 to lift up the pressure plate fig 8 above the crystal and loosen the crystal Then tilt the crystal and then loosen the setscrew again to fix the crystal with the pressure plate Then install the holder with the crystal in it to the rotation stage and check again if the beam Is clipped by the crystal see above Then check the tuning range again Laser safety Do not forget to fix the laser safety beam shield fig 5 3 ALWAYS BEFORE switching on the pump light 6 5 4 Cleaning the crystal Refer to 10 2 Cleaning optics Never use acetone to clean the BBO crystal 6 6 The compensator crystal Note The output beams will shift as the crystal is rotated due to the angle tuning of the BBO crystal and its dispersion This beam shift is a horizontal parallel beam shift which reaches max 2 2 mm There is no angular deviation However in some applications it may be useful to minimize the beam shift of the versaScan In this case the compensator should be installed Note The compensator is an uncoated quartz crystal The versaScan beam will be attenuated by at least 8 percent 6 6 1 Installation of the compensator crystal e Remove the compensator holder from its rotation stage Hold the compensator holder with your hands and loosen the two M3 screws fig 5 20 at the top Be careful not to touch any nearby optics e Insert the compensator crystal in the ho

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