Class Note for OPTI 696D at UA
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Date Created: 02/06/15
Optics Rules of Thumb Chunyu Zhao Oct 18 2006 What is a rule of thumb A simple rule that guides your work A simple calculation that provides you immediate solution and answer make first order approximations eg sinAtanAA A number that helps you make design decision Order of magnitude of some optical and mechanical properties Manufacturing capability Practical Optics Fall 2006 2 Photonics Rules of Thumb For quick and easy reference this is a handy compilation of proven photonics calculations that coverthe full range of photonics from optics to lasers and detectors These simpletoimplement calculations and rules let you keep your composure and provide immediate solutions and answers This is a succinct handy and unique reference for anyone working in the optical sciences Many of these rules have been used in the industry for years but this is the first time they have been 8 stematically collected While providin ai hthearte guide tothe lost art of estimation it aso s ows how you can quickly predict the impact of changes You ll develop a sense of wEat will work and what won t and be able to explain w y Practical Optics Fall 2006 3 How to use a rule of thumb Memorize it Know the limit of application Practical Optics Fall 2006 Contents General rules of thumb Rules of thumb mentioned in previous talks Rules of thumbs I often used Practical Optics Fall 2006 General rules Murphy s law If anything can go wrong it will Don t take chances Have a backup plan Think twice before touching anything that has been aligned Dirty optics should be cleaned only after great deliberation and with great caution Practical Optics Fall 2006 igure of Merits Domain Geometric limit Near Diffraction Limited Criteria in WFE gt17L 7L4 Figure of Merit RMS spot size RMS WFE Strehl ratio When Wrms007 SRO8 Diffraction spot diameter d W 24411 Total scattering loss 6 surface roughness in k 1m SR z 1 mumy 1221 I TIR 1 27w2 Practical Optics Fall 2006 Lens drawing Remus Powefl Clear apef Radius Ed e Drameter Thlckness ta erance neg d ame er dtamgetel lolerance CT tolerance wadge 13 589 TPF 513 20 6 3118 0 05 445 0 05 005 64 643 TPF 513 29 0 6 Notes V I All dlmensluns m lnches 52 2 Materral Dpllcal glass per MlLsG474 type 8K7 p Schutt No 517642 a nd 15158 0 0005 v 54 2 0 8 strrae Grade A rre anneal s1 3 Surfaces marked P pclrsfr to power rrregularrty P mdrcated C 4 Manufacturer per mllst l 3830 5 Surface qualrty 60 7 4n 5 Surfaces marked quot239 coat wrm hlgh effrcrency ccatrng wrttr average reflectance pet surface s U 5 from 420 r 680 rm 7 Surface marked 6 ne gnnd and blacken wrm no bulldup 8 Bevel edges at 45 degrees to o 5 max face wrdtlr DR 9 Drameter to flat 5 I9 952 REF wan surface sag of5 977 0 05 on surface 51 CHK APP Sample Element SCALE 7 Practical Opn39cs Fall 2006 Optical element tolerances Parameter Base Precision High precision Lens diameter 100 um 12 pm 6 pm Lens thickness 200 um 50 um 10 um Radius of curvature tolerance on sag 20 mm 13 pm 05 pm Wedge light deviation 6 arc min 1 arc min 15 arc sec Surface irregularity 5 fringes 1 fringe 025 fringe Surface finish 50 131 rms 20 131 rms 5 131 rms Scratchdig 160100 6040 2010 Dimension tolerances for complex elements 200 um 50 um 10 um Angular tolerances for complex elements 6 arc min 1 arc min 15 arc sec Bevels 02 to 05 mm typical 02 mm 01 mm 002 mm Base typical no cost impact for reducing tolerances beyond this Precision readily available may cost 25 more High precision need special equipment or personnel may coat 100 more Practical Optics Fall 2006 9 Optical material tolerances Parameter Base Precision High precision Refractive index departure from i 0001 00005 00002 nominal Refractive index measurement 1 3 x 10395 1 x 10395 105 x 10395 Dispersion departure from i 08 i 05 102 nominal Refractive index homogeneity i 1 x 10394 i 5 x 10396 i 1 x 10396 Stress birefringence 20 nmcm 10 nmcm 4 nmcm depends strongly on glass Bubblesinclusions gt50 pm 05 mm2 01 mm2 0029 mm2 Area of bubbles per 100 cm3 Striae Normal quality Precision quality Precision quality Based on shadow graph test Practical Optics Fall 2006 10 optical element mounting tolerances Parameter Base Precision High precision Spacing 200 um 25 pm 6 pm manual machined bores or spacers Spacing 50 um 12 um 25 pm NC machined bores or spacers Concentricity 200 pm 100 um 25 pm if part must be removed from chuck between cuts Concentricity 200 um 25 pm 5 pm cuts made without dechucking part Practical Optics Fall 2006 11 Mechanical Machining Precisions 1mm coarse 025mm standard precision 0025mm precision machining 0002mm high precision machining Practical Optics Fall 2006 12 Scratchdig 8050 commonly acceptable cosmetic standard 6040 acceptable for most scientific research applications 4020 Scattered light can begin to affect system performance 105 a precision standard for very demanding laser applications Practical Optics Fall 2006 13 Coating Bare surface reflection at normal incidence r Single layer quarter wave AR coating When n15 nc138 MgFZ REPo Multilayer AR coating achieves low reflection lt1 over a broad spectrum Vcoating reflectivity lt 01 at design wavelength Practical Optics Fall 2006 14 Metallic Coating Wavelength Range Coating Type nm Aluminum 4001200 Protected Aluminum 400800 Si203 layer half wave Enhanced Aluminum 450750 multilayer dielectric UVEnhanced Aluminum 250400 UV transmitted dielectric Internal Silver 4001200 an additional layer of either lnconel or copper Protected Silver 40020000 Bare Gold 70020000 Protected Gold 65016000 hard dielectrics Practical Optics Fall 2006 Average Reflectance o 90 87 93 86 98 95 99 98 15 Plastic optics Avoid flat or weak surfaces Dndt 100ppm C CTE 70ppm C In comparison For BK7 dndt 14ppm C CTE 71ppm C For germanium dndt 396ppm C CTE 6ppm C Practical Optics Fall 2006 16 Thermal impact on focal length n 1 Focal length F 1 AF 2 a L wAT vFAT n l dt n l dt dn vz 25 0 In VlSlble range Allowable focus shift for diffraction limited performance Material v x10396 Plastic 237 BK7 44 BaK4 03 BaK50 1 1 4 SK16 34 SF4 38 Germanium 127 ZnSe 35 AZ 2 21qu2 Practical Optics Fall 2006 17 CTE for Typical Materials Material CTE x10395 C Aluminum 23 Steel 10 lnvar 06 Zerodour 002 ULE 003 Practical Optics Fall 2006 18 Useful numbers 1 arcsec 5 urad 1 mdeg 3 arcsec 1 degree 160 radian 1 inch 254mm C 3E8 ms V 6E14Hz Practical Optics Fall 2006 19 Laser Coherence length CL 2L2 Al Far field diffraction angle D aperture size a D Gaussian Beams Waist c Rayleigh range ZR 247702 Divergence 6 1 70 Practical Optics Fall 2006 20 Diode laser Astigmatism 68nm Divergence 3OX1O degrees FAHM Polarization along the short axis Spectrum width 1nm Lasing wavelength increases as temperature increases Practical Optics Fall 2006 21 Aberrations of a conic surface Spherical aberration of a conic surface K conic constant R vertex radius of curvature Aberrations of offaxis conic sunaces aof iaxis distance 3 Practical Optics Fall 2006 10 SA 3 8R 3 COMA K quot 3quot 2R 2 2 ASTI Kr 3 2R Seidel formulas 1 SA W040 51 Z AWN Marginal ray y SH Z n u Chiefray y AS W222 5111 Z AzyA 1 Petzval Curvature SW 2 H26A W220P K A nl DIStOftl0nW311E SV XSm SIV A an A m Axral color C Ay 7 51 Transverse color CI AyA H 2 may nu y n Practical Optics Fall 2006 23 Petzval Curvature P Mimi 29 n n Complexity of lithography lenses is believed to be caused by effort of correction of Petzval curvature Positive lens has positive PC while positive mirror has negative PC Diffractive elements on flat substrate has no PC Practical Optics Fall 2006 24 Interferometer is an imaging system too Object point on mirro r ace Aberrations that matter Distortion Astigmatism Field curvature Null lens as imaoer Aperture stop located at interferometer focus Image of mirror Curved due to null lens Image scaled and distorted by null lens Practical Optics Fall 2006 25 Distortion correction morphing Phase map Phase map before morphing after morphing Interferogram Practical Optics Fall 2006 26 Grating equation n2 sin 62 n1 sin 61 m1 a Approximation A6 2 mi a Practical Optics Fall 2006 27 Optical testing with CGH Diverger lens CGH Interferometer Alignment CGH Test CGH Z Fringe spacing for test CGH 1St order Practical Optics Fall 2006 Cl DIN 28 Diffraction Longitudinal dimensions Wavelength 9 and Distance Z Transverse dimensions Slit width D and Beam width a at the observation plane ZocDa Practical Optics Fall 2006 29 Diffraction Fresnel zone plate nth zone radius W Talbot distance 2d2 Z T 1 gt 2d2 gZT ii 30 Ball alignment Align a ball interferometrically Interferometer m Al Pawer 2 Fn Beam f number 8 2 R Ball ROC xi mi i nm n Il39 2 fatearlal r iilaglignrietnt 2 39 Fn AT BeamWalkO 2 Y F 100 Practical Optics Fall 2006 31 Longitudinal magnification 2 mlong mtrans FWWZ If Lens L1 moves in 3 DOF how much wil F2 move Practical Optics Fall 2006 ill Focus F2 Conclusion Optical rules of thumbs help you avoid common mistakes and work efficiently Have your own list of rules of thumb Practical Optics Fall 2006 33
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