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MCAO Adaptive Optics Module Subsystem Optical Designs R.A.Buchroeder MCAO MCAO Optical Bench • In-plane optical layout, with room for electronics • f/16 input, f/33.4 AOM output • Image plane and exit pupil location match those of telescope • DMs, TTM, BS, ADC in collimated space • Gemini telescope plate scale 0.62 mm/arc sec • MCAO output plate scale ~ 1.30 mm/ arc sec May 24-25, 2001 MCAO Preliminary Design Review 2 MCAO Optical Paths Science path Beam splitters LGS focus NGS focus LGS path NGS path May 24-25, 2001 MCAO Preliminary Design Review Science focus 3 AO Module Optical Design Requirements MCAO Parameter Science Path NGS WFS Path LGS WFS Path Spectral passband, mm 0.85-2.5 0.5-0.85 0.589 Field-ofview radius, arc min 1 1 1 (width of square FOV) 90—200 km range Wave front quality 60 nm RMS uncorrectable and non-common path errors (59 nm at zenith; 96 at 45 degrees) 0.15 arc sec RMS spot size (120 nm RMS WFE) Peak subaperture tilts less than 0.1 arc sec (102 nm RMS WFE) Optical transmittance 0.75 (0.74 at 1.0 micron; 0.80 at 1.65; 0.82 at 2.2) 0.7 (0.46 at 0.5 micron; 0.69 at 0.7) 0.7 (0.65) Pupil imaging Worst case pupil motion of 3% on instrument cold stop (2% RMS) NA Worst case WFS-to-DM misregistration 10% of a subaperture width (6.8% RMS) Emissivity 19% NA NA Atmospheric dispersion at 45 degrees, arc sec 0.007 for 0.85+/-0.07 mm (0.002) 0.010 for 1.25+/-0.1 mm (0.0039) 0.013 for 1.65+/-0.1 mm (0.0019) 0.018 for 2.20+/-0.2 mm (0.0023) 0.05 NA May 24-25, 2001 MCAO Preliminary Design Review 4 MCAO AO Module Science Path May 24-25, 2001 MCAO Preliminary Design Review 5 MCAO H-band RMS wavefront error • Wavelength 1.65 um • ADC operating @ 45-deg zenith angle • Upper part of +/- one arc-min FOV; field is not rotationally symmetric. • Representative RMS May 24-25, 2001 MCAO Preliminary Design Review 6 Science Path: I-band w/o ADC MCAO Circle = 0.053 arc sec May 24-25, 2001 MCAO Preliminary Design Review 7 MCAO Science Path: I-band at Z = 45 deg Circle = 0.053 arc sec May 24-25, 2001 MCAO Preliminary Design Review 8 Science Path: J band @ Z=45 deg MCAO Circle = 0.08 arc sec May 24-25, 2001 MCAO Preliminary Design Review 9 MCAO Science Path: H-band Spot Diagrams • H-band, 1.55 to 1.75 microns • 2 arc-min FOV • With ADC operating @45deg Zenith Angle • Circle = Airy disc diameter = 0.103 arc sec May 24-25, 2001 MCAO Preliminary Design Review 10 MCAO Science Path: K-band at Z=65 deg Circle = 0.14 arc sec May 24-25, 2001 MCAO Preliminary Design Review 11 H-band Mapping error @ 45 degree Zenith Angle MCAO Maximum distortion: 1.9% May 24-25, 2001 MCAO Preliminary Design Review 12 MCAO Science Path ADC @ Maximum Correction • I-band (0.78- 0.92 um) to 65-deg zenith angle • Angular deviation = 0 at 0.85 um; could be tipadjusted for zero at Hband. • Different, smaller symmetrical counterrotations for J,H,K bands May 24-25, 2001 MCAO Preliminary Design Review 13 MCAO NGS Path Optical Layout May 24-25, 2001 MCAO Preliminary Design Review 14 NGS Path Image Quality MCAO • @45-deg zenith angle • Better at zenith • < 1 mm image runout wrt ADC rotation • Circle = Airy Disc • Secondary color OK due to abnormal dispersion glass types May 24-25, 2001 Circle ~ 0.04 arc sec MCAO Preliminary Design Review 15 MCAO NGS Image Mapping • Varies slightly with zenith angle • Shown here at 45-degree zenith angle • 1.3% distortion typical May 24-25, 2001 MCAO Preliminary Design Review 16 MCAO NGS WFS Design Concept May 24-25, 2001 MCAO Preliminary Design Review 17 LGS Path: General Requirements MCAO • Monochromatic @ 589nm • FOV = square one arc-minute on a side • Laser star range 90 to 200 km • Telecentric intermediate image plane • Pupil misregistration less than 10% of subaperture • Small noncommon path wave front errors • Transmittance goal = 70% (65% current performance) • Performance requires zoom focus adjustment, adjustable relay elements, and pupil alignment mirrors. May 24-25, 2001 MCAO Preliminary Design Review 18 LGS Optical Path Layout May 24-25, 2001 MCAO Preliminary Design Review MCAO 19 MCAO LGS “Zoom Optics” • LGS range 90 to 200 km •V-coatings @ 589nm for high transmission •Elements A and D fixed • Elements B and C form a ‘mechanically compensated’ zoom May 24-25, 2001 MCAO Preliminary Design Review 20 MCAO LGS Image Quality vs Range • Spot diagrams at intermediate focus • Residuals compensated by spot relay and LASER AIMING • Superimposed at 4 ranges • Marker = 200 microns • Circle = Airy disc May 24-25, 2001 MCAO Preliminary Design Review 21 LGS: from Zoom Optics to S-H Lenslet Array May 24-25, 2001 MCAO Preliminary Design Review MCAO 22 MCAO LGS: Wavefront at S-H Array • Representative case • Central laser star • 127 km range May 24-25, 2001 MCAO Preliminary Design Review 23 LGS: Mapping of DM0 to SH Plane • Best case; others similar MCAO Maximum Distortion 0.12 % • Central laser star • 127 km range • Distortions scaled up by 100X on this plot • By symmetry, 3 different collimators required. May 24-25, 2001 Pupil Map with distortion Magnified 100X MCAO Preliminary Design Review 24 LGS WFS: SH Focus to CCD Relay MCAO Adjustable relay reduces non-common path errors from 100 to below 10 nm RMS May 24-25, 2001 MCAO Preliminary Design Review 25 MCAO LGS WFS Relay: variable magnification mode • Geometrical spot diagrams • Results superimposed over magnification range • Circles = Airy disc May 24-25, 2001 MCAO Preliminary Design Review 26 MCAO LGS WFS: Relay Distortion May 24-25, 2001 MCAO Preliminary Design Review 27 MCAO Diagnostic WFS Design Concept • Insert into converging f/33.4 beam, pivot around exit pupil • 32x32 sub apertures on 10.4mm pupil ( 325 um lenslet size ) •1k x 1k CCD, 10 um pixel • Nyquist sampling @ 0.9 um • Sub aperture FOV = ~11.3 arcsec in object space May 24-25, 2001 MCAO Preliminary Design Review 28 NGS WFS Transmittance Estimate Wavelength 500 nm 700 nm Transmission per reflection 0.944 0.979 10 reflections 0.562 0.809 Science beamsplitter, net 0.990 0.995 NGS/LGS Rugate BS 0.950 0.950 NGS/LGS dielectric BS 0.850 0.850 Air-glass per surface 0.993 0.996 ADC net (4 surfaces) 0.970 0.984 Corrector Lens 0.986 0.992 APD Optical Path, Type A 0.79 0.82 APD Optical Path, Type B 0.91 0.93 With Rugate BS and Type A 0.40 0.61 With Rugate BS and Type B 0.46 0.69 With dielectric BS and Type A 0.36 0.55 With dielectric BS and Type B 0.41 0.62 MCAO Total transmission: May 24-25, 2001 MCAO Preliminary Design Review 29 LGS WFS Transmittance Estimate Wavelength 589nm Transmission per silvered reflection 0.962 9 silvered reflections 0.706 Science Beamsplitter net 0.980 NGS/LGS Rugate beamsplitter 0.990 NGS/LGS dichroic beamsplitter 0.850 Air-glass per surface optimized 589nm 0.998 4 element Zoom Lens Corrector 0.984 Collimator,dielectric mirror 0.998 Pupil Steering, dielectric mirror 0.998 De-anamorphoser lens 0.996 Shack-Hartmann Lens 0.996 6-group (8 element) SH-CCD relay lens 0.976 MCAO Total Transmission With Rugate BS 0.65 With dichroic BS 0.56 May 24-25, 2001 MCAO Preliminary Design Review 30 Optical Component Fabrication MCAO • Off-Axis Paraboloids, 3 required • Science Path Beamsplitter, water-free fused silica • Science Path ADCs, water-free fused silica and fluorite • NGS/LGS beamsplitter made from ordinary fused silica, with small wedge angle and a cylindrical curvature on R2. • NGS ADCs made from optical glass • LGS four spherical optical glass lenses • NGS sphero-parabolic optical glass lens • Off-axis aspheric collimator mirrors, 5 required • Afocal cylindrical deanamorphoser lenses, 5 required • Miscellaneous May 24-25, 2001 MCAO Preliminary Design Review 31 MCAO AOM Optical Design Summary • All optical issues have viable solutions • Relatively simple optical designs • Thanks to OAPs, assembly and deflection tolerances are liberal • Certain components are difficult and expensive to fabricate but prospective vendors indicate that they are feasible May 24-25, 2001 MCAO Preliminary Design Review 32 MCAO PDR Agenda Thursday, 5/24 0800 Welcome 0805 Project overview 0830 Science case 0930 Break 0945 System overview 1015 System modeling 1100 AO Module optics 1145 Lunch May 24-25, 2001 1245 AO Module mechanics 1340 AO Module electronics 1400 Break 1415 Beam Transfer Optics 1510 Laser Launch Telescope 1545 Closed committee session 1800 Adjourn MCAO Preliminary Design Review 33