Fabry-Perot Instruction Manual
Contents
1. Perfect Alignment with Fabry Perot Tuned to Input Wavelength FP Eye D Super fine Adjustment Upon completion of alignment with the adjustment screws final parallelism adjustment may be made with the bias controls using the methed of section 4 to check parallelism lf for optimal alignment one of the bias contro s is near the end of its scale it is a good idea to adjust the corresponding adjustment screw so that ail bias controls are returned 10 approximately mid scale This will allow for maximum flexibility in making future electrical adjustments E Survey of Mirror Flatness After the adjustments of sections 4C and have heen carried as far as possible it may be noted that the ring dia meter cannot be kept constant over the whole surface of the plates That is unless the mirror flatness is perfect ane can usually find mutually high or spots on the mirrors When the central ring is nearly collapsed the ring diameter will be extremely sensitive to plate errors since the ring diameter is a cosine function If such deviations seem excessive they are probably due to one of the following Causes 1 The mirrors may not have been properly mounted i e the mounting has induced strain in the mirror biank 2 The mirror blanks may not be up to specification 3 The coating may not be as flat as the substrate 4 The coating may have stressed the substrate One can often improve the fine2. 111 b instruction Manual Fabry Perot Lo A 9 CONTENTS 1 incoming Inspection A Visual Inspection of Shipping Container B D Visual Inspection of the Equipment Performance Inspection General Comments Instrument Description A TAM 3 2 Design Considerations for Burleigh s RC 110 RC 170 RC 140 or RC 150 Mechanical Design Choice of Materials PZT Material Adjustment Screws Assembly Model RC 110 and RC 170 Fabry Perots Model RC 140 Fabry Perot Model RC 150 Fabry Perot Mirror Holders Ramp Generators DAS Stabilization Systems Collimator and Mounting Brackets Thermatrol and Thermal Box Composite Kinematic Mounting Base Multipass Options Qo 3 Q Cn GI Operation A B RC 110 RC 170 or RC 140 Fabry Perot RC 150 Fabry Perot General Set Up and Alignment in the Visible UV and Near IR Ompmuntuvym Preliminary Discussion Rough Adjustment Fine Adjustment Super fine Adjustment Survey of Mirror Flatness Adjustment of the Collimator Final Adjustment PAGE m b amp ON ho 3 Fe 3 DOO 00 3 gt 3 CONTENTS CONTINUED 5 Alignment in the IR 6 Operational Hints 7 Troubleshooting 8 Specifications 9 Warranty 10 Outline Dimensions PAGE 10 11 12 12 13 14
3. y x UP d 1 1 INCOMING INSPECTION A Visual Inspection of Shipping Container The Burieigh RC Series Fabry Perots Ramp Generator and RC Series Mirrors are packed in specially designed containers according to sound packaging principals to prevent damage during shipment On arrival inspect the package carefully for any evidence of handling abuse If any is found contact your purchasing and or shipping departments immediately Instruct these departments inform rhe shipper ar his agent that damage to the shipping container has been found The shipper may wish to inspect the package before opening 8 Visual inspection of the Equipment Unwrap or unpack each of the packages carefully CAUTION Do not throw away any paper or packing material without first determining that nothing is enclosed Do not discard the shipping container until it has been established that there is no damage to the equipment You may also want to retain this container jor storage or transportation of the instrument Visually examine each item to be sure everything is included and identified on the packing slip Consult Sectian 2 for descriptions Next gently shake the instruments If arattle is apparent damage during shipment may have occurred Again notify Burleigh and the shipper through the appropriate channets lf you determine that an item has been omitted from your order recheck the shipping container If nothing is found ple
4. Diverge the laser on to a white card with a spot size approxi mately equal to the plate diameter It should now be possible to see fringes by looking in at the B mirror side Figure amp Alignment with Large Collimated Beam Misaligned Three Fringes Card Lens l Laser Figure 10 Viewing Fabry Perot Circular Fringes with Eye again as shown in Figure 9 Since the pupil of the eye is only a few mm in diameter it sees only local fringes generated by a corresponding small cross section of the mirrors By moving the head up and down or sideways the fringes will be seen to expand or contract unless the mirrors are already aligned perfectly An opening up of the rings means that the plate separation is increasing and a closing down means that the separation is decreasing If the central fringe is almost collapsed this technique is extremely sensitive Thus one can tell immediately which way the mirrors must be tilted about an axis perpendicular to the head movement in order to improve mirror parallelism By adjusting each of the two orthogonal adjustment screws and by repeating the sequence several times the mirrors can be brought into nearly perfect parallelism very rapidly The operation will proceed most rapidly if the head motian is always perpendicular to the two orthogonal axes about which the adjustment screw in question rotates the mirror Figure 9 Alignment with Large Collimated Beam
5. 110 140 150 RC 170 Scan Method Mirror Separation RC 110 140 RC 150 RC 170 Linearity with Burleigh Electronics PZT Linearity Scan Hysteresis Adjustments movable mirror mount fixed mirror mount Read Outs cavity spacing screws Finesse Performance 110 RC 140 RC 170 RC 150 Super Invar construction Aluminum Suner IEnvar and nvar 50mm 70113111 Thermally compensated dual PZT assembly 1 25um scan in ER models 1 75um alignment 0 150mm 10mm 0 50mm with spacers 0 170mm 0 1 amp 1 over 1um amp 1 over lum manual sliding to set gross cavity spacing PZT alignment to 500 precision range 1 75um Super Invar screws 250um turn 2 25 alignment sensitivity with 2 delrin knobs Scale and vernier reads to 1mm 0 02mm if calibrated dials read to 5um depends on mirrors peu performance section Fabry Perot Mirrors Material RC 600 Series RC 800 Series Flatness 550nm surface 1 surface 2 Holder Coating Wedge RC 600 Series RC 800 Series Collimator Construction Length Pinhoies Adjustments Lens Focal Length Mounting Multipass Option Type Aperture RC 22 3 pass RC 22 pass RC 27 3 pass RC 27 5 pass X Y adjustment Corner cube quality Entrant surface coating Housing and masks Mounting Bases Type Vertical adjust Elevation adjust Azimuth adjust Length standard 13 RC 600 Series R
6. axis 1 optic axis 5 a tilt about horizontal axis I optic axis 250 D Dimensions dg ZI in 47 1 42 z 5 RCAI RCA7 COLLIMATORS A Instrument Description Burleigh s 41 and RC 47 Collimators are normally used 35 light collectors with RC Series Fabry Perot interferometers A large diameter tong focal length about 250mm F L achromatic doublet is focused onto a pinhole thus controlling the angular extent of radiation passing through the Fabry Perot which is incident on the detector Refer to the Fabry Perot Tech Memo for further detail on the optical systern it is also recommended in high contrast systems that a collimator be used at the input side This will serve to elimi nate radiation with an unacceptable angular extent thus reducing the possibility of unwanted stray light and scatter The aperture of the collimator is matched to the usable aperture of the Fabry Perot optics The RC 41 used with SOmm optics has 3 48mm aperture The RC 4 for optics has 68mm aperture The doublet can be precisely focused onto the planc of the pinhole A visible eyeicns 15 included simplify this adjustment A series of precision 50 100 200 and 500um ate muunted and centerear romovalic holders se 1 the proper diameter can bracketed depending the sy
7. be used if they are calibrated The scale is zeroed at the factory for a typical set of mirror holders Standard factory setting allows the cavity to be read to an accuracy of 0 1mm due to machining tolerances and mounting errors If a spacing accuracy of greater than about 0 1 mm is required the adjustment screw scales and dials should be calibrated with the mirrors in place The scale can then be read to 5 2 Loosen the three tube clamps on the moveable support plate inat rides along yhe Super Invar rods Slide lhe moveable support plate to the end opposite the other mirror mount Tighten the clamps Stand the instru ment on each end and inseri 1he RC 600 Series mirrors into your Fabry Perot with the screws provided The mirrors are mounicd in special Invar holders The Fabry Perot plates have 4 wedge angle of 10 15 are min The point of maximum thickness is marked by an arrow scribed onto the edge of each plate note this arrow also points to the first surface The plates should be mounted in the Fabry Perot such that the arrows on cach plate 1809 apart in order 10 minimize angular beam deviatton through the Fabry Peror L i 2 Be careful not to pinch the cable Also when placing the Fabry Perot on end make sure the micrometers do not damage the sapphire V blocks 3 Set the desired mirror spacing The mirror spacing is given by the 0 150mm scale reading minus the 0 16mm reading on the lar
8. constructed of 1 Emm thick walnut stained birch The control pancl located on the top of the box consists of two switches three LED s and 3 amp slow blow fuse Figure 1 The scnsing and control circuitry as well as the power supply is located inside under the control panel The interior is lined with 19mm thick urethane for excellent thermal isolation Heater elements are bonded to metal radiating plates which are then attached to the insulated inner walls Thermatrol RC 75 CONTR TEMP 1 The upper portion of the RC 75 is removed from tha base by releasing the four stee dip latches A cutout for feeding through the electrical connection to the Fabry Perot 15 provided on the bottom side of the upper section coated utility windows are also supplied with each instrument The standard 50 8mm 76 2mm in the RC 77 diameter windows AR coated for the visible These windows are easily removed should the user desire to change or replace them The base of the RC 75 is large enough for an RC 24 Composite Kinematic Mounting Base which permits several degrees of 0 anda adjustment as well as approximately 12 7mm of vertical adjust These adjustments are useful for properly aligning the entire Fabry Perot with respect to the incoming radiation The RC 24 is normally mounted in RC 75 at the factory although it can be done in the field with little
9. have been accurately machined so that they will be close ta the exact center of the large hole on the X Y slide Thus the working pinhole will now be within about 25um of the correct position USE CAUTION WHEN VIEWING THE BEAM TO AVOID EYE DAMAGE THE INTENSITY OF THE BEAM SHOULD ATTENUATED AS MUCH AS POSSIBLE Specifications Construction Aluminum Length 280mm nominal Pinholes 50 100 200 500um Adjustments Orthogonal micrometer adjust of pinhole location Aperiure 48mm RC 41 411 RC 41UV 68mm RC 47 RC ATIR RC 47UV Lens Focal Length 254mm visible models only very distant object throuwgir an open window and adjust the Mounting Three 10 32 clearance holes located collimator objective lensantil the image of the distant object 3 4 5 dia bolt circle Affixes to seems ta be suspended inspace at the plane of the hole RC 41 1 mounting brackets 41 1 Focusing is now complete and the collimator may be affixes coilimator to work bench with attached to its base four 4 20 screws on a 4 square hole pattern Laser Collimator Card i Fabry Perot Lens Eyepiece 7 Figure 2 Viewing Fabry Perot Circular Fringes through Coilimator Pet DO Oulline Dimensions B buleicn Burleigh Instruments Inc Burleigh Park Fishers NY 14453 716 924 9355 Teiex 97 8379 FP275 1281
10. or the RC 75 or it can be used freestanding Multipass Options The RC 22 Multipass Option allows 3 pass or 5 pass operation of the RC 110 or RC 140 Fabry Perots with any SE Mirror Set The apertures or 5 pass are T1mm or 5mm respectively The RC 27 allows 3 pass or 5 pass operation of the RC 170 with a RC 690 Mirror Set and provides apertures of 15mm or 9mm respectively Consult the Fabry Perot cata og the Multipass Option Tech Memo for more etail OPERATION RC 110 RC 170 or RC 140 Fabry Perot To set up the RC 110 RC 170 or RC 140 for operation consult Figure 4a Figure 45 and the following directions Kear Plate Split Tube Clamp Movable Plate Cavity Length Scale Super Invar Rods PZT Drive Assembly Adjustment Screws Centering Screw Adjustable Plate Figure da RC 140 Fabry Perot RC 110 similar but constructed entirely of Super Invar Figure 4b RC 170 with 27 Multipass Option 1 Carefully remove the cardboard and tape around the plate controlled by the screws Note that this screw piate ts held off the end plate by three screws Carefully extend the adjustment screws until they seat in the sapphire V biacks and move the screw plate off the end plate Now the three screws in the screw plate can be removed The cavily spacing is read with the cavity scale There is no direct correlation to scales and dials on the adjustment screws although they can
11. pinhole The pinholes have been accurately machined so that they will be close to the exact center of the large hole on the x y slide Thus the working pinhole will now be within about 25um of the correct position USE CAUTION WHEN VIEWING THE BEAM TO AVOID EYE DAMAGE THE INTENSITY OF THE BEAM SHOULD BE ATTENUATED AS MUCH AS POSSIBLE Collimator Eye ee ees ee Lens Evepiece Figure 11 Viewing Fabry Perot Circular Fringes through Colfimator 10 G Final Adjustment 1 Finesse As a check on the overall alignment of the Fabry Perot and to make any final touch up adjustments that may be necessary one should observe instrument finesse in the electronically scanned mode That is with a photomulti pher or photodiode located behind the pinhole the output of the detector should be connected to the vertical amplifier of a scope The horizontal amplifier should be driven with either the output 100 from the Ramp Generator or the time base of the scope by triggering it with the trigger output of the Ramp Generator The spectrum of a cw laser should then appear as a series of sharp peaks on the screen See Figure 12 scan time of 50ms to 100ms provides a nearly flicker free presentation on the scope screen that is tasy to view Small pinholes can be precisely centered on the fringe pattern by adjusting each micrometer screw on the x y pinhole slide such that the fringes move in one dire
12. slight stiff feel to the Adjustment Screws To maintain the best stability lubricants must be Check all screw connections Gently press on PZT assembly at How to Determine Cause kept to a minimum and the spring loading force must be large With a small amount of lubricant and strong springs the screw threads will feel stiff Better feel will result from a lighter spring load but stability might be reduced n optimum compromise must be determined experi mentally To ensure an adequate spring force for hotding the screw plate against the adjustment screws the springs should be extended approximately one half inch ar more E The sapphire V blocks that mate to the tungsten carbide ball ends of the adjustment screws are very hard and can easily be damaged by a sharp tap or allowing the adjustable plate to fall against the screws The Fabry Perot should therefore be handled carefully at all times 7 TROUBLESHOOTING A Symptom Possible Cause How to Determine Cause B Symptom Possible Cause How to Determine Cause Symptom Possible Cause No Scanning of cavity Electronic controller not connected Electronic controller malfunction No incident electromagnetic radiation Wrong mirrors for incident radiation Detector malfunction Check all connections See separate electronic instruction manual Recheck coating curve Check detector operation Severe deterioration of finesse across sca
13. the top of the glass spheres to hold them firmly against the grooved pads Thus the mirror position is well defined mechanically and thermalty with no forces which can stress or distort the mirrors See Figures 2 and 3 RC Series Mirror Sets are mounted with this technique Mounting Mirror 1st surface Invar Holes gt protrudes about 0 1mm V pad Mirror Cell Spring ring Mirror Figure 2 f E Da au Figure 3 Burleigh Fabry Perot Plate Mounting Technique Each mounted mirror is then secured in the interferometer with three screws The advantages of this method are the mirror surface is precisely referenced to the invar ring such that when the invar rings of both mirrors of the cavity touch the mirrors can protrude slightly from their holders to allow for very small mirror spacings The method results in a design which is well constrained for rigidity and does not distort the mirror surfaces C Ramp Generators The Burleigh 43 or RC 44 Programmable Ramp Generators are designed to operate with the RC 110 RC 370 RC 140 or RC 150 Fabry Perots Consult the separate instruction manual for operation D DAS Stabilization Systems DAS 1 and DAS 10 Data Acquisition Stabilization Systems authomatically correct for cavity drift and misalignment of the Fabry Perot Refer to the Fabry Perut catalog for further detail E Collimator an
14. 0mm aperture and accepts RC 690 Mirror Sets flatness guaranteed over 80 of the aperture There are a number of convenience features too For instance the cavity length scale reads to 1 mm Tha Super invar adjustment screws let you precisely change the cavity spacing by less than The screws are metric And the convenient dial can be read to Sum The exposed Super invar parts of th RC 110 are chrome plated The PZT drives are constructed of laminated PZT discs connected electrically in parallel A thin wafer of rigid low thermal expansion Alumino Silicate ceramic 15 laminated to each end of the stack to provide electrical isolation The PZT stack assemblies are bonded between Invar plates to form an integral PZT drive assembly Aluminum shields prevent accidental touching of the PZT stacks which have up to 1000v applied This construction technique produces a thermally compensated assembly of minimum length maximum sensitivity and rigidity It also allows easy inter changeability between PZT assemblies T 7 Model RC 140 Fabry Perot The mechanical configuration of the RC 140 is identical to the RC 110 The only difference is the materials used in the construction The end plates and spider are made of aluminum instead of Super Invar Care is taken to define thermal expansion reference planes wherever Super Invar parts are attached to the aluminum support members This insures that the expansion of the aluminum does
15. 37 Thermal Boxes A Instrument Description RC 24 Composite Kinematic Mounting Base A Instrument Description B How It Works l Attaching the RC 24 2 Mounting the Fabry Perot on the RC 24 3 Specifications C Specifications D Outline Dimensions RC 41 RC 47 Collimators Instrument Description Adjustment of the Collimator Specifications Outline Dimensions PAGE jt bJ AAG 01 C4 C1 C3 Qi 8 1 GENERAL Introduction This instruction Manual describes several popular options for Burlcigh s RC Serics Fabry Perot Interferometer They have been included in one manual since most customers order two or more of these items with their Fabry Perot system The RC 75 and KC 77 Thermatrol Enclosures and RC 34 and 3 1 Thermal Boxes arc used to house the entire Fabry Perot They insulate the systerns and keep the precision optics dust free The RC 24 Mounting Base which can be mounted inside the thermal enclosures allows for positioning of the entire Fabry Perot and includes a Super Invar reference plane as well as kinematic support The RC 41 and RC 47 Collimators are used at the output of the Fahry Peror to collect the transmitted light series of interchangeable pinholes control the angular extent of the interfering rays B Unpacking Al Burleigh instruments are shipped in heavy duty cartons which protect the unit during nor
16. C 800 Series used Silica ZnSe A 100 or 4 200 2 10 invar high reflectance multi layer dielectric on surface 1 AR on surface 2 Aluminum 275mm nominal 50 100 200 500um orthogonal micrometer adjust of pinhole location 254mm visible models only Three 10 32 clearance holes located on a 4 5 dia bolt circle Affixes to 41 1 mounting brackets RC 41 affixes collimator to work bench with four 14 20 screws on a 4 square hole pattern RC 22 RC 27 Coupled corner cubes 11mm amp mrn 15mm 9mm 1 16 5 10 sec Multi layer AR for R 0 5 Black anodized aluminum 24 Cumposite kinematic 1 5cm 10 39 Super Invar Thermatrof Enclosure RC 75 Size 19 x 10 x 105 Insulation 34 to 1 polyurethane alumized Mylar Super insulation Construction stained birch Temperature Stability lt 0 055 Ambient Range 220 39C 9 WARRANTY Burleigh Fabry Perots are warranted against defects in material and workmanship for a period of one year after date of delivery and the return of Burleigh s warranty card During the warranty period Burleigh will repair or at its option replace parts which prove to be defective when the instrument is r turned prepaid to Burleigh Instruments Inc Before return of an instrument always call Burleigh for approval of the return The warranty will not apply if the insturment has been damaged by accident misuse or as resu
17. ase call Burleigh for possible corrective action C Performance Inspection word about Burleigh s Quality Control Every effort is extended to insure that the instrument shipped to you works according to specification 41 is very expensive to have a defective instrument returned to the factory and to have an unhappy customer As an example of Burleigh s Quality Control your unit has undergone numerous visual inspections individual testing of active parts and extensive long term testing of the complete assembly However with sophisticated instruments very small or subtle shipping damage may which could seriously affect performance In view of this please inspect the instruments as soon as possible after receipt so any problem can be promptly identified and corrected D General Comments Each unit shipped is assigned a Burleigh serial number Please refer to this number during any phone conversation or written communications Do not return your unit to Burleigh without obtaining a return authorization number Unauthorized shipping can void any claim you or Burleigh may have against the shipper or his agent 2 INSTRUMENT DESCRIPTION A Design Considerations for Burleigh s RC 110 170 RC 140 or 150 1 Mechanical Design The RC Series Fabry Perots are designed with particular emphasis on freedom from angular and axial cavity drift with lime aud temperature See Figure T The mainframe ts designed w
18. atch to make each set of screws Different batches of the same metal can have varying coefficients of thermal expansion a serious problem in screws made withhigh expansion materials These differences are less important in the Burletgh screws because they are made of Super Invar instead of some other material with a larger thermal expansion The second advantage is that the thread engagement of each of the screws is always closely matched For instruments using a differential screw adjustment it may be necessary to make significant adjustments to the differential screws in the process of mechanically aligning the mirrors The threads will not be engaged identically for ali three differential screws meaning expansion of each screw shaft is controlled from a different point This can introduce angular drift in the instrument due to temperature changes This problem can be significant in steel differential screws 5 Assembly Ail Burleigh interferometers are designed with hard connections between mechanical and piezoelectric parts There are no soft plastic materials compliant joints or RTV like substances to creep and move these are major causes of misalignment and drift problems in Fabry Perots 6 Model RC 110 and RC 170 Fabry Perots The RC 110 and RC 170 are general purpose scanning Fabry Perot interferometers with superior thermal and mechanical stability They are constructed almost completely of Super invar The end pla
19. boratory conditions it generally takes one to two hours to achieve equilibrium but under some conditions 25 much as four hours Note 1f the laboratory environment is well controlled and free of drafts superior Fabry Perot performance may be obtained by not using the temperature control feature of the y 75 11 should always be determined which mode af operation is best for your laboratory conditions iod D Troubleshooting Test Poinis The reference point for all voltages is AC neutral To observe Lie AMET wavelorms on an oscilloscopc the scope line cord must be AP sa 18 11 on P isolated from earth ground three prong to kwo prong unb Tin adapter serves the purpose Phe oscilloscope s ground can now he connected te AC neutral at minus deof C4 and bids sugested that 4 mulu 3 RC 34 RC 37 THERMAL BOXES A instrument Description In the following description the RC 34 will be used in all examples statement however also apply to the RC 37 Thermal Box for Burleigh s 70mm Fabry Perot System KC 34 Thermal Box is identical to RC 75 Thermatroi except that it does not include active temperature control The construction is of 1Tmm birch lined with 19mm urethane insulation Removable windows AR coated for the visible seal the interior of the RC 34 from drafts The RC 34 provides a well insulated dust free enclosure for Burieig
20. ction e g always to the left s a micrometer is advanced or retracted from the center of the fringe pattern Figure 13 Also it may be possible to sharpen up a laser line by making slight adjustments of the transducer bias controls The optimum mirror parallelism can be achieved this way 2 Slope Trim in a Fabry Perot Interferometer if the tnree piezoelectric scanning elements have slightiy different sensitivities tilting during scanning will result The amplitude of the fringe pattern in each free spectral range will change as the Fabry Perot scans through several free spectral ranges indicating less than optimum alignment at some point during the scan If you observe this effect the slope trim controls can be used to compensate for the differential sensitivities of the piezoelectric elements 11 is very convenient to use the three bias controls to determine the relative sensitivity of the stacks before making this adjustment To do this turn the SLOPE TRIM controls approximately turn clockwise Use the ALIGNMENT controls to align the Fabry Perot optimally for the first order in the scan The amplitude of the subsequent orders will decrease Observe the 1251 order and bring it into optimum alignment with the ALIGNMENT controls Note which control or controls are used ta make this adjustment Reset the controls to align the first order Now adjust the SLOPE TRIM control or controls corresponding with the controls no
21. d Mounting Brackets Some imaging system must be used to collect the light at a pinhole The RC 41 Collimator uses a 48mm aperture achromatic lens of a nominal 250mm focal length and a set of x y positionable pinholes for this purpose Interchange able pinholes of 50 100 200 SO0um are easily screwed into the x y slide Two micrometer heads provide precise adjustment of the pinhole location at the focal point of the lens pinholes are precision laser drilied and mounted in holders All elements of the collimator are mounted in one tube The RC 41 1 Mounting Bracket is recommended This bracket positions the collimator at the correct optical axis height for the RC 110 RC 170 RC 140 or RC 150 F Thermatrol and Thermal Box The RC 75 Thermatro js an insulated temperature controlled enclosure for ali Fabry Perots t maintains the temperature to lt 0 059C The RC 34 Thermal Box is a passive enclosure it is an RC 75 without temperature control and has 4 polyurethane insulation inside a walnut stained box The windows are removable G Composite Kinematic Mounting Base The RC 24 Composite Kinematic Mounting base provides 0 angular adjustment as well as vertical positioning for all Fabry Perots Super Invar 15 used to reference the end plates and the positioning is kinematic for stress free mounting and precise repositioning on the optical axis The RC 24 can be ordered mounted in the RC 34
22. difficulty The RC 75 can actively control the temperature of a Fabry Perot to an accuracy of 0 19C for 69C room temperature change The probe assembly found inside the box is to be attached to the Fabry Perot by way of the magnets on its side The best locationis the side of the adjustable mirror plate It 15 advanta geous to appty a small amount of thermal grease to the probe to aid heat transfer The operating temperature is preset to approximately 299C or 339 depending on switch setting and will bring the Fabry Perot to 1 15 temperature in approximately one to two hours B How 11 Works meter be used in place of the oscilloscope for the voltage measurement This unit uses 3 1 amp slow blow fuse The temperature is sensed with a thermistor in a precision on the front pancl Do not use any other type of fuse bridge network The bridge signal is then amplified and compared to a stable reference ramp generated in the control circuitry The zero voltage switch takes this information and through 1 13 proportions ihe amount of power supplied to the heaters for regulation of temperature 1 With linc cord unplugged check operation of thermistor Resistance at jJ 1 9 and 1 11 should be approximately 2 2K 2 at 259C 2 With power on supplies al posilive side of C4 and C How Use The Thermatrol Enclosures pin 4 of UT LM324 should both read 6 8 2 O 5VDC Place the magnetic thermistor probe on th
23. e device to be 3 Output at pin 7 of U LM324 should swing from controlled On Burleigh mode Fabry Perois the best position ground to 3 voils probe heated and cooled heating for the probe is on the side of the adjustable mirror plate can be by holding probe in handj On other instruments it is best to experimentally determine the optimal sensing point The device to be controlted is then 4 Reference ramp at positive side of C5 should run placed on the wooden basc and the upper portion of the from 1 5 volts to 4 volts DC in an to 10 sec interval RC 75 is latched into place Make sure any direct electrical connections to the Fabry Perot are fed through the cutout If any of the test points indicated above are different than A tightseal is very important for proper operation The latches described contact Burleigh for further troubleshooting and line up with the top for one orientation only to avoid tedious repair suggestions system realignment every time the top is removed Check the RC 75 for correct operating voltage which will be either E Specifications 110 220 Each RC 75 is wired for one of the above voltages and should the user desire to rewire for a different Power Thermatrol enclosures are wired line voltage consult Surleigh for details Plug in the line cord atthe factory for either 110 or Tum the power switch to the ON position A LED immediately 220 VAC operation change above t
24. econd reason is discs have a higher d or piezoelectric coefficient than PZT cylinders This allows a shorter PZT drive further improving thermal stability The compactness also minimizes cantilevering of the drive mirror and strengthens the assembly The third reason 5 that discs ensure a more rigid mechanical construc tion Discs have a larger surface area in the direction of expansion and more closely approach a solid member Disc assemblies are therefore less prone to resonances when driven _ at high frequency l 4 Adjustment Screws The all Super Invar adjustment screws used in the Fabry Perots have very high resolution capability with greater than 10mm adjustment range This is necessary for precisely setting the mitror spacing and alignment for final mechanical alignment of the mirror cavity The adjustment screw assembly uses 250um turn metric threads with 5cm diameter Delrin knobs for improved resolution and metric readout Adjustments to 1 10um are easily made With the scale and dial the screw position can be read to 5um and interpolated if necessary There are two other advantages to the Super Invar screws which are not realized with other types of screws One advantage 15 the inherently reduced sensitivity of the interfero meter cavity to thermal perturbations Beside the advantages of the Super Invar with its lower absolute thermal expansion there is the advantage offered by using metal from the same b
25. ge knobs The accuracy is about 0 1mm for a more accurate indication the spacing must be accurately measured for each mirror set 4 The RC 41 Collimator can be attached to the RC 41 1 Mounting Brackets 5 Connect the 10 foot cable to the Ramp Generator or DAS The connector contains seven leads for bias ramp functions and ground B RC 150 Fabry Perot Jn general operation of the RC 150 is the same as the operation of the RC 140 with the following exceptions See Figure 5 Gross cavity separation is governed by Super Invar spacers These spacers are of specified lengths in 10mm increments The RC 150 does not have a cavity scale so the spacing must be measured The adjustment screws can be calibrated and used to set and read the cavity spacing to 5um within their 10mm range Super nvar Spacer Rods PZT Drive Assembly 150 uses same front plate with adjustment screws and adjustable plate as RC 140 Figure 5 RC 150 Fabry Perot General The PZT stacks have Alumino Silicate end insulators and epoxied to the plates of the PZT drive assembly This package is attached to the Fabry Perot with three screws 11 is easily removed or changed if an infrared PZT drive is required for example 4 SET UP AND ALIGNMENT IN THE VISIBLE UV AND NEAR IR A Preliminary Discussion Aligning of the interferometer is most easily accomplished by using a small cw laser e g He Ne laser as the source Althou
26. gh such a source is not absolutely necessary for small plate separations it becomes increasing y vital for rapid and easy adjustment as the plate separation becomes large d 1cm t is not necessary that the laser wavelength correspond to che reflectivity peak of the mirror coatings even 20 reflectivity at the laser wavelength is adequate Mirrors for the visible UV and near IR can normally be aligned with this technique if the substrates are transparent to the gas aser wavelength Alignment consists of two major operations Laser Card with Hole 1 Making the mirrors parallel 2 Making the pinhole of the collimator coincident with the central spot of the Fabry Perot fringe pattern The formal operation usually proceeds in three steps 1 An initial rough adjustment using the adjusting screws 2 A fine adjustment using the adjustment screws 3 super fine adjust using the PZT stacks For convenience the mirror adjusted by the adjustment screws shall be referred to as and the mirror adjusted by the PZT drive assembly as B At this point connect the Ramp Generator as described in 115 operating manual B as controls should be set to mid position The ramp should be turned off and each pot in the Slope Trim Section turned fully counterclockwise The power light should be on B Rough Adjustment First it is necessary to make the laser bearn perpendicular to the mirror B as shown in Figure 6 The laser should be se
27. h Fabry Perots 1t protects the instrument from the effects of drafts or rapid temperature changes The RC 24 Composite Kinematic Mounting Base can be attached inside the RC 34 on the base section for 9 a and vertical adiustment of the Fabry Perot t is recommended that the RC 24 be attached to the RC 34 at the factory but it can be fitted in the field with little difficulty The dimensions of the RC 34 are identical to the RC 75 Consult the appropriate paragraphs of the RC 75 section of this manual for tips on setting up the RC 34 4 RC 24 COMPOSITE KINEMATIC MOUNTING BASE A instrument Description The RC 24 is designed to provide three functions First it provides three degrees of angular adjustment of the Fabry Perot about three perpendicular rotation axes 8 and a as well as approximately 12 7mm of vertical adjustment These adjusunents necessary to properly align the axis of the Fabry Perot with respect to the optical axis of the system Second it provides a Super Invar stabilized mounting reference for the Fabry Perot This insures that the end plates of the Fabry Perot are not stressed by forces exerted by thermally induced length changes in the Fabry Perot support The Super Invar length standard is itself mounted such that it cannot be affected by the aluminum top plate of the RC 24 Third the RC 24 provides a three point kinematic support for the Fabry Perot to allow removal and precise repositioni
28. he power switch should light indicating that AC power the line voltage consult the is present Consult the troubleshooting section should the unit factory fail to operate in this manner Fuse 1 amp Slow Blow Temperature Control 2 0 19C for a 69C room ele d the set points labeled high and low temperature change which are selected wi control temperature switch These 1 two ranges are provided so the user optimize operation for Standard set Points 29 and 3300 his own particular laboratory environment The standard Outer Dimensions 505mm L x 302mm W x operating temperatures are 339 and 299C for high and low 323mm H respectively Other set points are available The user should Inner Dimensions 416mm L x 223mm x consult the factory for further details including urethane 238mm H 24 5L Clear Aperture Two temperature deviation LED s give an indication of the RC 75 47mm sensor temperature relative to the set point chosen with the RC 77 70mm control temperature switch The upper LED lights when the temperature is 0 19C higher than the set point and the lower Optical Axis Height 114 3 2mm comes on when the temperature is 0 19C lower than the Height of fret 952mm set point Both will remain off when the temperature control ler is operating to within 2 0 9C of the set point Depending F Qutline Dimensions on the mass of the object in the box the set point selected and the la
29. ith three fold rotational symmetry the symmetry of an equilateral triangle about the axis normal to the mirror plane This necessitates that the PZT drive elements and Super Invar rods be located at 1209 This design approach helps assure the maintenance of mirror parallelism over long periods of time The Super Invar adjustment screws are located at 909 for orthogonal adjustment but vertical symmetry is still maintained Figure 1 RC Series Fabry Perots RC 170 not Shown 2 Choice of Materials Each of our Fabry Perots use Super Invar Invar low thermal expansion ceramic insulators and low thermal expansion PZT material in a reentrant design to control the spacing of the mirrors in the Fabry Perot cavity Every mechanical part directly affecting the thermal stability of the RC 110 170 140 150 is machined of Super Invar 0 36 x 10 9 0 or Invar 1 6 x 10 5 0C This includes sleeves drive plates mirror holders adjustment screws and rods n fact because the is reentrant there zero axial drift at some spacing Also by judicious placement of thin metal washers it 15 sometimes possible to make the axial drift zero at a selected cavity spacing For optimum performance the environment should be thermally very uniform and slowly changing The 110 and RC 170 are made almost completely of Super Invar The use of similar materials throughout added to the extremely low thermal expan
30. lt of modification by persons other than Burleigh personnel Thermal Box RC 34 Size Insulation Construction 19 x 10 x 109 polyurethane Super nsulation stained birch 10 OUTLINE DIMENSIONS RC 110 140 302 ie 19 a dimensions if mm 93 51 RC 150 Hm 14 2 56 tap 3 places 1200 68 3 Dia B C each end i 12 170 22 56 7 3 places amp on B8 b 14 28 Tapped 127 on 88 9 4 Places Attach at one end only buleich Burleigh Instruments Inc Burleigh Park Fishers NY 14453 716 924 9355 Telex 97 8379 FP 265 581 Fabry Perot Options Instruction Manual 1 Thermatrol 2 Thermal Box 3 Mounting Base 4 Collimators ria 8 ae Se a ES DA SD a u per cr 1 es TE E eee ye 7 eee de eee re ere Se d CONTENTS 1 ON p gt General Introduction Unpacking Warranty RC 75 RC 77 Thermatro Un Temp erature Controlled Enclosures Instrument Description B How It Works C How To Use The Thermatrol Enclosures D Troubleshooting Test Points E Specifications F Outline Dimensions RC 34
31. mal handling and transpor tation f the outside of the shipping carton is damaged notify your shipping department immediateiy The shipping department may wish to notify the carrier at this point 11 the shipping carton is undamaged the instrument should be removed from the carton If damage is evident visually notify your shipping department and Burleigh Instruments Inc immediately Warranty Burleigh products are watranted against defects in material and workmanship for a period of one year after date of delivery with the return of Burfeigh s warranty card During the warranty period Burleigh wili repair or at its option replace parts which prove to be defective when the instrument is returned prepaid to Burleigh Instruments Inc Before return of an instrument always call Burteigh for approval of the return The warranty will not apply if the instrument has been damaged by accident misuse or as a result of modifica tion by persons other than Burleigh personnel 2 RC 75 RC 77 THERMATROLUm TEMPERATURE CONTROLLED ENCLOSURES A Instrument Description in the foilowing description the RC 75 will be used in all examples All statements however also apply to ihe RC 77 Thermatrol enclosure for Burleigh s Fabry Perot System gt The RC 75 provides a well insulated dust freg enclosure for Burleigh F abry Perois and can bc used control the lempera lure of the Fabry Perot in 2 0 19 The shell is
32. n duration Eiectronic controller malfunction Poor electrical connection to one PZT stack Mechanical separation of PZT discs Separation of PZT stack assembly from invar support plates Incorrect Slope Trim setting Check ali connections for electrical continuity Check PZT assembly for broken or separated elements Siope Trim Instrument doesn t hold alignment Fractured sapphire V blocks Clamps not tight on Super Invar rods Dirt or other particulate matter between mirror holder and support plate Mirror holders loose In support plates Mirrors loose in holders of tab loose on mirror Broken or loose PZT stacks location of each stack while scanning Fringes should return t original peak height when pressur is removed if not problem may be there Remove mirror holders and clean mirror support plate Recheck as above Retract adjustment screws and remove springs so adjustable plate may be removed inspect sapphire V blocks with magnifying glass Smali localized fractures or a major fracture can be caused by allowing the adjustable plate to snap into position against the adjustment screws when the springs arc in plave 11 fractures are observed the V blocks must be removed and replaced or removed and re epoxied into the plate so only good surfaces are exposed Make certain no epoxy remains on surfaces of V blocks 8 SPECIFICATIONS Fabry Perots Type RC 110 RC 170 RC 140 RC 150 Aperture RC
33. ng of the Fabry Perot This feature can be very useful when aligning a complex optical system The three point mounting also insures that the Fabry Perot cannot be warned nr stressed B How To Use RC 24 1 Auathing the RC 24 The amp 24 is secured to the base of the RC 75 or RC 34 or to an optical bench with four 4 20 screws in the bottom plate of the RC 24 The top plate is removed by carefully detaching the spring and lifting The holes in the bottom plate can be used 35 a template 1 the REH is being attached 10 an exist ing RC 34 of RC 75 the urcthane the base of these enclosures must be carefully to exactiy the RC 24 2 Mounting the Fabry Perot on the RC 24 The Fabry Perot should rest on the RC 24 secured only by its own weighi Two special ball end stainless screws provided wilh the RC 24 should be screwed into the holes in the bottom of the front end plate of the Fabry Perot until they seat Then the Fabry Perot is placed so tha these ball end sercws seat in the bore and slot in the top of the RC 24 with the rear end plate resting on the Super invar reference strip CAUTION Always remove the Fabry Perot from the RC 24 Mounting Base before transporting the system Unless great care 15 taken 61 to tilt the assembly the Fabry Perot can slip loose and be damaged C Specifications Vertical adjustment 127mm 8 tilt about horizontal axis 1 optic axis 3 tilt about vertical
34. not affect stability Aiuminum has good thermal diffusivity to minimize the effects of thermal gradients 8 Model RC 150 Fabry Perot The model RC 150 is especially designed for those who do not need large cavity separations The RC 150 is similar to the RC 140 in mechanical construction The difference is the cavity separation scheme employed The RC 150 uses Super Invar spacers to determine the cavity spacing instead of continuously varying the spacing by sliding one mirror mount relative to the other gross cavity separation of the KC 15U can be changed discreteiy using the optiona Super Invar spacers The optional spacer set permits cavity spacings from 1 to 5cm in increments of 1cm For cavity separations between the fixed values above the fixed mirror mount can be translated 0 5cm by adjusting the three adjustment screws B Mirror Holders Two of the most important considerations in Fabry Perot Interferometry are the mechanical rigidity and thermai stability in the mounting of 4 200 plates or mirrors Mounting must be accomplished without stressing or distort ing the mirrors With Burleigh s mounting method three invar tabs epoxied to the edge of each mirror These tabs have glass spheres secured into holes bored into each tab The mirror with tabs 15 then placed into an invar holder with three small hardened V groove pads at 1209 The glass spheres sit in these groovcs and a spring load is applied to
35. nt through a hole in a card approximately 1mm Jn dia meter By adjusting the angular position of the laser or the interferometer the beam retlected from B can be made to pass directly back through the hole Fabry Perot LFA Figure 5 Alignment of Fabry Perot Perpendicular to Beam transmitted beams are now viewed on a distant screen as shown in Figure 7 adjusting the angular tilt of A with the adjustment screws the spots on the screen may be made coincident This completes the rough adjustment OQ Misaligned Partially Aligned Aligned Figure 7 Alignmegt with Small Glameter Visible Laser Beam Fine Adjustment At this point two techniques can be used If the Fabry Perot is illuminated with a large collimated laser beam severa straight line fringes will be observed on a white card at the output See Figure 8 The plate separa tion increases by A 2 for each fringe observed Thus if six fringes are observed the plates will be tilted by 6 x A 2 across the diameter of the beam Using the adjustment screws and PZT s if desired the plate alignment can be improved until there are no fringes in the field Perfect alignment will result when the cavity is tuned with the PZT s to transmit the source wavelength and the observed light field is symmetrically illuminated See Figure 9 Ifa collimated source is not available the laser beam can be used Rearrange the light source as shown in Figure 10
36. s a Function of Pinhole Position 6 OPERATIONAL HINTS There are of course methods of operating the RC 110 RC 170 RC 140 or RC 150 that you ll develop through use of the interferometers Here are some areas that you should watch however Operation of the interferometer an isothermal environment will improve the performance of the interfero meter Burleigh s RC 75 Thermatrol Enclosure or RC 34 or 35 Thermal Box is recommended B The adjustment screws are lubricated with a specially selected lubricant which provides optimum stability None theless one should allow a period of time for the lubricant to displace from between the threads and the instrument to equilibrate after an adjustment is made 1 k Ramp Generator is being used there some points to consider 1 The 20 and 50 millisecond ramp rate should be employed only for alignment and cursory spectral analysis 2 The ramp waveform is rounded at the initiation and end of the ramp The purpose is to minimize oscillation af the driving mirror from mechanical resonance effects caused by the rapid change in ramp voltage during retrace 3 The rounding on the ramp waveform is a constant and at ramp rates longer than 20 milliseconds it is a negligible contribution to scan non linearity 4 For R PZT drives it may be necessary to operate at ramp durations of 200ms to 15 to obtain optimum linearity 12 D There may be a
37. sion of the Super Invar means optimum thermal stability The added mass of the Super Invar also helps insure mechanical stability The RC 140 and RC 150 use Super Invar and regular invar for mechanical parts directly affecting the cavity spacing Alumi num is used elsewhere Aluminum is a proper choice because of its excellent thermal diffusivity Thermal gradients are rapidly diffused throughout the instrument body to inhibit L7 misalignment found interferometers using iron or other similar materials Since the aluminum is not used where it can influence the cavity spacing thermal performance is maintained 3 PZT Material All Burleigh Fabry Perot Interferometers use matched sets of PZT elements to provide electrical parallelism adjustment of the interferometer cavity as well as electrical scanning over its free spectral range The PZT elements are constructed from interferometrically matched PZT discs The PZT material used for scanning offers the best linearity and hysteresis character istics less than 196 inter order linearity and 1 2 hysteresis With the Programmable Ramp feature of Burleigh electronics the scan linearity can be reduced to 0 1 A high sensitivity material 15 used for a large alignment range There are three reasons PZT discs are used instead of PZT cylinders The first is discs have a lower coefficient of thermal expansion than cylinders This greatly improves the thermal stability of the Fabry Perot The s
38. sse of an instrument by using a smaller aperture to limit the incoming beam to the ML 1 7 Laser Card Fabry Perot LE best section of the mirror Burleigh Fabry Perot plates normally have a slight spherical deviation from perfect flatness Burleigh tests all mirror sets for flatness before shipping Adjustment of the Collimator The focus of the collimator lens must first be adjusted This is accomplished before the collimator is attached to its base Screw the pinhole device containing the eyepiece lens into the X Y slide Note that this device contains a rather large hole approximately 3mm in diameter in fieu of an actual pinhole Adjust the eyepiece lens until the edge of this hole is seen clearly in sharp focus The edge of the hole is in exactly the same position along the axis of the objective lens as that of the actual pinholes Now look ata very distant object through an open window and adjust the collimator objective lens until the image of the distant object seems to be suspended in space at the plane of the hole Focusing is now complete and the collimator may be attached to its base With the Fabry Perot illuminated as in Figure 11 view the ring pattern through the eyepiece lens of the collimator Adjust the lateral position of the eyepiece with the two micrometer screws such that the ring pattern is exactly concentric with the large hole The eyepiece may now be unscrewed and replaced with the working
39. stem Micrometer driven Xa Y sage is used lo position the pinhole tiin wth collimators are with optics for the infrared or UV as designated by thewffixes IR or UV Initial cus and adjustment magrequire more effort 35 i normally case in non visible seems and the visible eyelens may not usable The 41 1 Collimator ounting Bracket 15 recommended This bracket will simpiifgfree sunding mounting of the Colimator which has 3 dlindrical body B Adjustment of the allimator The focus of the lens must first be adjusted This is accomplished befmge the collimator is attached to its base Screw the device containing the eyepiece lens into the X Y slide Mote that this device contains a rather large hole approximately 3mm in diameter in lieu of an actual pinhole Adjuszthe eyepiece lens until the edge of this hole is seen clearlyin sharp focus The edge of the hole is in exactly the same position along the axis of the objective lens as that of e actual pinholes Now look at ac 4 With the Fabry Perot illuminated as in Figure 2 view the ring paiiern inrough the cyepices lens of the collimator Adjust the lateral position of the eyepicce with the two micrometer screws such that the ring pattern is exactly concentric wit the large hole The eyepiece may now be unscrewed and replaced with the working pinhole The pinholes
40. ted above such that all orders have the same amplitude After repeating this procedure a few times all spectral orders should approximately equal intensity indicating the PZT scan is free of tilt 9 ALIGNMENT IN THE IR If the substrates are not transparent to the visible alignment is more difficult If a laser source is avaitahle however alignment can be accomplished without undue difficulty First by measuring the actual plate positions relative to each other the plates should be aligned to about 0 001 to 0 002 Now if this Fabry Perot were to be illuminated with a Jarge collimated beam and if the output could be viewed ten or fewer straight line fringes would be observed 10 6um This fringe pattern can be effectively determined by illuminating the Fabry Perot with a small laser beam traversing the beam across the plates in X and or traversing the Fabry Perot itself collecting the through put with a lens and plotting the detector output Thus the effective fringe pattern and therefore plate alignment can be determined By changing the alignment and repeating the process the Fabry Perot alignment can be improved until the transmission is symmetric over the plates when tuned to the source wavelength Figure 12 Fabry Perot in Scanning Mode Showing Partial Alignment and Perfect Alignment A00 m 11 Pinhole to Left Pinhole Centered Figure 13 Fringe Position a
41. tes rods sleeves mirror mounts and even the adjustment screws are Super Invar The thermal expansion of Super Invar is amp 0 36 x 10 6 0 about 5 times lower than regular invar a 1 6 x 10 5 0C For comparison stainless steel has an 9 6 x 10 5 0C and brass has an 11 4 x 106 Low thermal expansion means stability is maximized RC 110 and 170 are piezoelectrically scanned using three PZT elements operated in parallel and made from Burleigh s low hysteresis low expansion high linearity PZT 7 material The PZT stacks are interferometrically measured and matched for tilt free scanning Alignment is accomplished with three high sensitivity elements for a large adjustment range The mirror spacing of the RC 110 ts continuously variable from 0 to 150mm and the RC 170 from 0 to 110mm This allows an optimum compromise between free spectral range and resolution Split tube clamps lock the moveable mirror support plate firmly in place after the gross cavity spacing isset The split tube clamps are precision honed Super invar sleeves These sleeves have a 1 5 1 length to diameter ratio to allow the spider to slide smoothly along the precision ground Super Invar rods without marring or binding The RC 110 provides up to 50 8mm clear aperture and is compatible with standard Burleigh Mirror Sets which allow maximum 50 8mm clear aperture flatness guaranteed over 80 of the aperture The RC 170 has a 7
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