Class Note for OPTI 696D at UA
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Date Created: 02/06/15
OptiGQGBX Practical Optics Seminar College of Optical Sciences The University of Arizona Interferometer Alignment November 15 2006 Sen Han PhD Veeoo Instruments Inc Tucson Arizona Outline Practical interferometers Alignment procedure mrnary What is interferometer Interferometry is a study of interference between wavefronts of light beams exiting the same source 4 ltgt gt Interference Interferometer is an optical device that divides a beam of light exiting a single source like a laser into two beams and then recombines them to create an interference pattern Applications of interferometer Typical Parts Measured Optics flats spheres torics aspheres prisms substrates windows Semiconductor Products wafers MEMS packaging material Data Storage hard disk read heads disks suspensions MEMS pressure sensors accelerometers micromirrors Cutting and Grinding Implements drill bits razors sandpaper Food and Drug Products cereal chocolate pills Medical Implants stents hip implants bioMEMS Precision Machine Parts air bearings engine blocks fuel injectors airplane wings Coatings AR drug coatings anticorrosion coatings Typical Measurement Results FlatnessShape Critical Dimensions Roughness Depths and Volumes Film thickness Dynamic Response Types of interferometers Michelson Interferometer MachZehnder interferometer Fizeau interferometer TwymanGreen interferometer Mirau interferometer Reference BS Michelson Interferometer l w a Sample Applications MEMS Semiconductor products Medical implants TTM interferometric Objective MachZehnder interferometer M as BS Applications Data storage a Hard disk read heads 1 Micro lens Beam quality Fizeau interferometer Applications Optics 39 H Semiconductor products Data storage MEMS Precision machine parts BS 7 Applications Infrared optics Rough surface parts H H Mirau interferometer BS I I Sample Applications Semiconductor products Data Storage MEMS Cutting and grinding implements Food and drug products NT8000 Medical implants Precision machine parts 10X 20X Coatings 50x Outline Practical interferometers Alignment procedure a Summary 11 Alignment Goals Reproducible results across systems Often want kinematic mechanics Easy to use and understand Used by nonengineers in production Want to be able to go back months or years later to repeat without relearning process Document everything and take pictures Alter overall mechanical design as little as possible Minimal fiducial holes Little extra fixturing Avoid alignmentonly optical elements if possible Do not overengineer use the loosest tolerances required to achieve results 12 General procedure Generating a reference line using a laser along each critical path Aligning flats beamsplitters mirrors prisms camera Tiptilt in both X and Y directions Placement along optical axis Sometimes rotation as well Aligning lenses Sidetoside and updown translation Tiptilt in both X and Y directions Verifying real light source on the space lighting Adjusting the focus of the lenses and camera 13 Example 1 106um interferometer for LIGO REFERENCES 1 Sen Han et al Retrace error for the measurement of a long radius optic ICO Technical Digest Vol 3749 597598 1999 2 Sen Han et 611 Design of an interferometer for the measurement of long radius optics SPIE Proceedings Vol 3966 2000 14 Laser Interferometer GravitationalWave Observatory UGO Optics of extremely high quality with apertures of up to 250 mm are needed f39t f4 Requirements for design and alignment 106um wavelength 6 Fizeau phase shifting interferometer Magnification 1X amp 6X Spatial scales 10cm 1mm Sample ROC Radius of curvature 75km 145km M1OOPV for focus and astigmatism coefficients k1000RMS for residual surface after removal of focus and astigmatism terms ROC measurement accuracy lt 3 Retrace error lt 6nm PV for 4 fringes of sample tilt 16 Real product Designed optical layout L2 L3 M2 BS L4 CCD M3 M1 Fold mirrors M1 M2 and M3 Beam splitter BS Camera CCD Lenses L1 L2 L3 and L4 Light source S L1 18 Alignment procedure Place 2 fiducials for each segmented lighting Adjust alignment laser so that it passes through first two fiducials Align each fold mirror and beam splitter until the beam passing through following 2 fiducials Align each lens and make sure the beam passing through the center of the eachlens Setup the real light source on the optical axis Adjust the focus of each lens and camera until getting sharp image Fiducial Alignment laser Retrace error Retrace error refers to the calculated OPD optical path difference map difference between null and nfringe cavities It is very IMPORTANT for the long ROC measurement of LIGO optics It can be modeled by ray tracing It needs to measured and subtracted if necessary 20 Simulated r etrace error using ray tracing software 211 nm PV with tilt term of 4 fringes 056 nm PV after removal of tilt term Two key affecting factors Coma magnitude xzm2 Z7Z angle tanquot C 2 6 Astigmatism magnitude Z42 Z5Z ZS C Z4 Zx is Zernike coef cient Z4 and Z6 are function of horizontal tilt ZS and Z7 are function ofvertical tilt 21 angle tan Coma and astigmatism vs RF tilt I d t I39d tE39 M N quot Vertical tilt F39u39ui Re ne Emir mm quot f quot m Mt Tll iv am my Horizontal tilt 291 I31EI39Ev l Flt E Ht lt ID it ll LJ at r n i mi Fi39u39 In Fm run Em L El 45a 3 0 I 1 Tit uj rrr39irurlal n rgei Retrace error of real system 184 nm PV and 026 nm RMS at 4 fringe tilt and average of 60 sets after the accurate alignment 23 Other errors Effect of the movement of focus lensf t and selection of reference location on system magnification Distortions in X and Y directions Measuremenlnlsysumn nl Znnm Senlx Measuremem nl 5ysem Dlsnllnn annm Se n Ix mm e mm mm 7 m mmnw e m iim m1x ism mam 7 mmr nmmm mums as u Diredian x r pixei spanng Diredian v r pixei spacing m i v i v quotm7 mm k mm SH SH m 2n 2n m SH SH SH SH m 2n n 2n m SH SH immense mummy gtlt Disiaiiian caefiicieni 4 mm Elna gtlt ms ii em 5 Basssww gtlt Disiaiiian offset in mzsazs mi Pamquot 3o 4m x Disiaiiian caefficieni in x HMS iii my in x Disiaiiian offset n mi Pamquot in v Disiaiiian caefiicieni a US252 Uii y HMS N W Ii 578592DU7 y 0mm anger n M27855 Mm pawquot l7 i275i v Disiaiiian Daefficieni 174 US252 nii v HMS iii my If 578592 nnf v Disiaiiian unset n M7855 vim pawquot I 712m Disiaiiian paints editing Disiaiiian paints editing Na x v in gtlt i m M i 3525 m n52 n25937 i was an n7 nzsaaz 2 7 3D 5 95 El 69 I 25892 Deieie item Ahaii Finished 2 7 58 S 82 El 69 I 25897 Deieie item Abaii Finished 3 5259 552 use nzsm 3 585 am n58 nzsaos niacinquot af anaiysis niacinquot aranaiiw r minim r XDiieciian r YDiieciian r Dehugimagss r Dehugimages 24 Final ROC measurement Three measurement results 584 km 585 km and 587 km The ROC was independently established to be 6 km 25 Example 2 24 phase shifting interferometer for NIF project REFERENCES l 2 3 Chiayu Ai et al Design of a 24 Phase Shifting Interferometer SPIE Proceedings 1997 Sen Han Calculation of Iris Size in 24 Fizeau Interferometer SPIE Proceedings Vol 3782 464 468 1999 Sen Han Laser Alignment for 610 mm Large Aperture Fizeau Interferometer SPIE Proceedings Vol 3782 469473 1999 26 LLNL s NIF project National Ignition Facility LLNL Lawrence Livermore National Laboratory During an ignition event all 192 beams will simultaneously converge on a 10 m diameter target chamber holding afusion target the size of a dime 27 First 24 phase shifting Fizeau interferometer 28 Requirements In NIF project more than 8000 planar optics must be optically measured Optics have aperture size on the order of 40x40 cm Some of these optics will be used at Brewster s angle Because the parts will not be wedged so in transmission and reflection test the use of TM and TE polarized light eliminate their surface reflections and associated spurious fringes respectively High spatial resolution High wavefront accuracy 29 Optical configuration at Brewster s angle TM Transverse magnetic field polarized light is used in transmission test TE Transverse electric eld polarized light is used in re ection test 30 Diffraction effects Transmittance of a weak grating in doublepass TDx 1 2jacos7flcos27m 0 Acceptable spacing A2 3 82 A the grating s period 50 the phase constant 7 the wavelength of light or the amplitude of the grating 0lt or 1 31 Requirements of laser alignment RMS intensity uniformity 25 and rolloff 50 Polarization extinction uniformity 90 Polarization state rotation of the laser source within 1 degree error Intensity center coincides with the mechanical rotation center Less than 1 fringe between transmission flat and corner cube 32 Option1 Whole light source rotation ColhmatOr ObJeCUVe Intensity center Diode laser Attenuator S u l39A l I 0 D Mechanical rotation axis Adapter Diverging lens Tube Pinhole Less than one fringe between TF and CC TF CC Option2 Wave plate rotation Collimator Objective Diode laser Attenuator Intensity center Mechanical rotation axis Diverging lens 39 Results after rotation M No visible change in the intensity centered profile of the full aperture l Wave plate tilt within 1 degree No effect of the small shifting distance in axis on the intensity centralization Not blocking the beam by 15 um pinhole during the wave plate rotation Other concerns Extra fringes Polarization characteristic Feedback Small tilt gtgtgt power loss within 1 Otherwise unstable 36 37 Time number of phase7c 415 395 40 405 mJ M 41 42 425 0 0L 0 m Relative distribution of transmission intensity 0 COJgtU103J 0 oo 0 co L quot R R R 64 R 87 4 contrast 87 025 contrast 51000 Extra fringes M 39u39 39 Long amp short axis intensity percent Polarization characteristic 100 I T W i J l 9 l l l i 80 l l l H Long axis intensity zero order 70 if I Measured values 60 77 Short axis intensity zero order 50 if x Measured values Long axis intensity multiple order 40 i 0 Measured values 30 if Short axis intensity multiple order Measured values My 20 f 10 39 39quot39quot 0 a I i 0 5 1O 15 20 25 30 35 40 45 Rotation angle of wave plate degree axis I0 lcosz0r B sin2 or sin2 B sin2cIgt2J 38 Polarization characteristic 120 00 iii 1 It CO O jl D O A O Transmission N O O C L 39quotquotn r39 o 620 640 660 680 Zero order Wavelength nm Multiple order First 24 phase shifting Fizeau interferometer Dual beam 6 and 24 40 Example 3 RitcheyCommon testing using a commercial interferometer REFERENCES l Sen Han et al Application of RitcheyCommon test in large at measurement SPIE Vol 4399 131136 2001 2 Sen Han Mike Zecchino Ritchey Common Testing of Large Flats Using a Commercial Interferometer Veeco Application notes 2003 41 Problems for large flats on the order of 1 m 0 Design a large aperture interferometer Large optics required are expensive Large optics required carry long lead time Largest system is still less than 1m in size 39 Or Stitch together many smaller measurements A large translation stage is required It is difficult to stitch many measurements on very at optics without introducing errors 42 Solution RitcheyCommon testing A A Common Note on Testing Polished Flat Surfaces Royal Astron Soc Mon Not 48 1056 1888 G W Ritchey On the Modern Reflecting Telescope and the Making and Testing of Optical Mirror Smithsonian Contributions to Knowledge 34 3 1904 Power a common error for large flat appears as both power and astigmatism in the test wavefront sin2 6 WZ O z 2COSGCOS26 1SZ 0 quotFESZ Z 4 Standard 4Sinze commerc1al W2 2 z 52 0 ZCOSG 2 1SZ 2 1nterferorneter cose cos 6 S surface error w wavefront error 6 RitcheyCommon angle incidence angle at large at TS T Large at Cat s eye Multiple measurements are necessary which rotate the flat at O 30 180 deg 43 Equipment list Interferometer Return sphere Transmission sphere 5aXis mounts Large Vibration isolation system Alignment laser Pinhole at Erasable marker Fine and stranded Wires Hexagon sample 44 Aligning and focusing the system Procedure Set up the interferometer Loadalign the TF Loadalign the test at into its position exactly perpendicular to the aperture Rotate the at adjust the tiptilt control and verify that it remains aligned throughout rotation Adjust the intensity to below saturation Replace the TF With the RS Place the pinhole at at the cat s eye Position the two 5 aXis mounts Position the at as closely to 45 Adjust the tiptilt and position of the RS until the beam passes back through the pinhole Verify that the test beam is roughly centered on the RS Mark the position of the mounts for later repeating test 45 Other procedures Measure Ritcheycommon angle Rs ssic ab COSG Large Flat 1 s abc 2 Measure the empty cavity with the help of three 39 crosshairs 46 Empty cavity with fiducial analysis muman x Fiduual lY FiducialZX FrduualZV39 Fuduualak FrductalZY quualax w Fiduual lY rmumal x w deucxal Y a mmmmx FrdumaIBY 7 Measurement Parameters ma namqname onl pmm wmmnr Wavelength 532 an Wedge o 50 mam 733 x430 mm 322 0 no Date mam2000 Tune 0920 41 pix pm Dix pix pIX nm um 00 5001000 1500 2000 2500300035004000 000 man 200 n 400 737604 0 500 0 emu nu tummy Maw 47 a 00 Multiple measurements E IV I 5 30 900 150 1 600 1200 if 180 48 Error sources Ritchey angle lt 05 degrees Rotating angle lt 01 degrees Error of reference sphere Error of return sphere Turbulence Vibration 49 Comparison of RC test with direct measurement Q RitcheyCommon test Direct measurement RMS is 196 nm RMS is 225 nm and PV is 11115 11111 and PV is 1215 nm 50 Example 4 Microscope interferometer REFERENCE 1 Sen Han Der Shan Wan IMOA Alignment Procedure Veeco documentation 2006 51 Optical layout Measurement W Signal Detector Array 111th Beamsplitter llluminator 4 Translator Microscope L39 htS 1g ource Objective Field Aperture Stop StOp Mirau Interferometer Sample 52 Alignment requirements All optical axes have to be aligned Illumination axis for color source1 Illumination axis for color source2 Image axis All axis shifts due to tilt parallel glasses Light sources align with objectives 5X objective 50X objective Intensity uniformity Less than intensity data Ra40 for 5X Less than intensity data Ra70 for 50X NT9800 53 Procedure I Tools 3alignment lasers 5fiducials Procedure Step1 1st laser passing through CCD hole 2fiducias Step 2 l quot 2nd laser passing through source1 hole 2fiducias Step 3 3rd laser passing through source2 hole 1 fiducial Step 4 Adjust dichroc mirror Step 5 Adjust folding mirror Step 6 Maybe repeat steps through 5 54 Uniformity for 5X objective Ralt40 y Ede EdIt Havgwave ENE YSWS Qutvut Dataizase ODEDHS Mndaw deb ew thions ardware Helg D Bquot M E 351139 m EWWWAH E MW f vjvwm M gt Mag 50 um 1027200c Wu 4 W M m M V W V Mode Intensity Raw Surface Data Time 135540 3 Raw Surface Stats 7 253 n 539 s Rava 488m Rva 4000am 5 5 szA 11 mu 7 MD Setup Parameters 235 3126 640x480 Z Samplmg 198nm 23D r 2250 r 2200 2130 Color 2 n 1 2 3 N 5 6 7 n 5 1 M I I I I I I I I I I l 953 Note Ready C PROGRANIWVKOVI5IDH 7 i i 7 WW quottens W E ew thions ardware Helg D E g 5 Q g 93 g QMMMAH 33 1 11m j Jn Ap rwmmn4 rv39JJMNwrw u dvgV Mag 50x Date 10quotl7quot200 Mode Intensity Raw surface Data Time 140218 1 quay Raw Surface Stats r 2550 szRa 243 mu szRq 310 mu 25 Rvat 4000 Inn 7 MD RawAvg 2 527quot 7 mm Setrllp Parameters SIZe 640 X480 235 U Sam 1m 1 98um p g r ZSDEI r 2250 7 2200 7 man an m 02 03 m 05 06 07 na EIB1EIM 1213 Title Note mm c pnoemnwwowm F I If NW 5 5 ch WWVWwWWI N r Uniformity for 50X objective Ralt70 nten tv 3 52 521 H2222 252052 21225 22525222 025252 05220 525 x mew thions Hardware He DE 095 113 H112 ma lmlwkulq 11 0 E m 1 Mav 0x Date 10272002 k quotquot J vquot N W 39Ixx 2WM I quot quot Www Mode Intensity Raw Surface Data Time 13 40 E f Raw SIII39I39Me Stats 2 255 u Raw R21 395 um 5 3 Raw Rq 488 mn g RawR 40001111 39 5 I 24112 mu 2 2222 g Setup Parameters 2 2352 g 3126 640x480 Samplmg 198nm 13 2 225 u 2 2222 g C I 2 i 1 1 1 I Title 85 3 Note 522220 7 pnoenmnwvmw 1 1i1 17 W 5510212521 5212 Haviwave 2520515 922222 02222252 020255 Mndaw 5212 a a E A 311 m1 QMMMAM 33 1 WW N rWWenu Mu AmaHm w v Mag 50 x Date 1027200 W 5 Veeco Mode Intensity Raw Surface Data Time 140218 ew thions Hardware Helg Raw Sunrace Stats 5 255 n 2 2500 g Rath 40001111 7 m D Raw Avg 24527 nm 5 2m Scull Parameters 2 S126 640 X480 735 U Sam 1m 1 98um i P g 2 252 2 2 2250 5 220 n g 5 2150 5 J i ID I1 I2 I3 I6 I5 IE I7 IE IS 1U 11 1213 I 5 I u I Title 95 3 J39 Note 56 222w pnoem1wvKo052522552m25 1m 11 1 1 WM Outline Practical interferometers Alignment procedure Summary 57 Summary Interferometer alignment has been playing a important role in various interferometer manufacturing Although a design is cool the real performance of the design might be very poor if the alignment is not correct or there is no way to align it well Design is a key Alignment is a ensure 58
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