MCAO Adaptive Optics Module Subsystem Optical Designs R.A.Buchroeder

MCAO May 24-25, 2001MCAO Preliminary Design Review2 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

MCAO May 24-25, 2001MCAO Preliminary Design Review3 Science path LGS path NGS path Beam splitters LGS focus Science focus NGS focus Optical Paths

MCAO May 24-25, 2001MCAO Preliminary Design Review4 ParameterScience PathNGS WFS PathLGS WFS Path Spectral passband,  m Field-of- view radius, arc min 111 (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) NAWorst case WFS-to-DM misregistration 10% of a subaperture width (6.8% RMS) Emissivity19%NA Atmospheric dispersion at 45 degrees, arc sec for 0.85+/-0.07  m (0.002) for 1.25+/-0.1  m (0.0039) for 1.65+/-0.1  m (0.0019) for 2.20+/-0.2  m (0.0023) 0.05 NA AO Module Optical Design Requirements

MCAO May 24-25, 2001MCAO Preliminary Design Review5 AO Module Science Path

MCAO May 24-25, 2001MCAO Preliminary Design Review6 H-band RMS wavefront error Wavelength 1.65 um ADC 45-deg zenith angle Upper part of +/- one arc-min FOV; field is not rotationally symmetric. Representative RMS

MCAO May 24-25, 2001MCAO Preliminary Design Review7 Science Path: I-band w/o ADC Circle = arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review8 Science Path: I-band at Z = 45 deg Circle = arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review9 Science Path: J Z=45 deg Circle = 0.08 arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review10 Science Path: H-band Spot Diagrams H-band, 1.55 to 1.75 microns 2 arc-min FOV With ADC Zenith Angle Circle = Airy disc diameter = arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review11 Science Path: K-band at Z=65 deg Circle = 0.14 arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review12 H-band Mapping 45 degree Zenith Angle Maximum distortion: 1.9%

MCAO May 24-25, 2001MCAO Preliminary Design Review13 Science Path Maximum Correction Science Path Maximum Correction I-band ( um) to 65-deg zenith angle Angular deviation = 0 at 0.85 um; could be tip- adjusted for zero at H- band. Different, smaller symmetrical counter- rotations for J,H,K bands

MCAO May 24-25, 2001MCAO Preliminary Design Review14 NGS Path Optical Layout

MCAO May 24-25, 2001MCAO Preliminary Design Review15 NGS Path Image zenith angle Better at zenith < 1 mm image runout wrt ADC rotation Circle = Airy Disc Secondary color OK due to abnormal dispersion glass types Circle ~ 0.04 arc sec

MCAO May 24-25, 2001MCAO Preliminary Design Review16 NGS Image Mapping Varies slightly with zenith angle Shown here at 45-degree zenith angle 1.3% distortion typical

MCAO May 24-25, 2001MCAO Preliminary Design Review17 NGS WFS Design Concept NGS WFS Design Concept

MCAO May 24-25, 2001MCAO Preliminary Design Review18 LGS Path: General Requirements 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.

MCAO May 24-25, 2001MCAO Preliminary Design Review19 LGS Optical Path Layout

MCAO May 24-25, 2001MCAO Preliminary Design Review20 LGS “Zoom Optics” LGS range 90 to 200 km 589nm for high transmission Elements A and D fixed Elements B and C form a ‘mechanically compensated’ zoom

MCAO May 24-25, 2001MCAO Preliminary Design Review21 LGS Image Quality vs Range Spot diagrams at inter- mediate focus Residuals compensated by spot relay and LASER AIMING Superimposed at 4 ranges Marker = 200 microns Circle = Airy disc

MCAO May 24-25, 2001MCAO Preliminary Design Review22 LGS: from Zoom Optics to S-H Lenslet Array

MCAO May 24-25, 2001MCAO Preliminary Design Review23 LGS: Wavefront at S-H Array Representative case Central laser star 127 km range

MCAO May 24-25, 2001MCAO Preliminary Design Review24 LGS: Mapping of DM0 to SH Plane Best case; others similar Central laser star 127 km range Distortions scaled up by 100X on this plot By symmetry, 3 different collimators required. Maximum Distortion 0.12 % Pupil Map with distortion Magnified 100X

MCAO May 24-25, 2001MCAO Preliminary Design Review25 LGS WFS: SH Focus to CCD Relay Adjustable relay reduces non-common path errors from 100 to below 10 nm RMS

MCAO May 24-25, 2001MCAO Preliminary Design Review26 LGS WFS Relay: variable magnification mode Geometrical spot diagrams Results superimposed over magnification range Circles = Airy disc

MCAO May 24-25, 2001MCAO Preliminary Design Review27 LGS WFS: Relay Distortion

MCAO May 24-25, 2001MCAO Preliminary Design Review28 Diagnostic WFS Design Concept 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 0.9 um Sub aperture FOV = ~11.3 arc- sec in object space

MCAO May 24-25, 2001MCAO Preliminary Design Review29 NGS WFS Transmittance Estimate Wavelength 500 nm700 nm Transmission per reflection reflections Science beamsplitter, net NGS/LGS Rugate BS0.950 NGS/LGS dielectric BS0.850 Air-glass per surface ADC net (4 surfaces) Corrector Lens APD Optical Path, Type A APD Optical Path, Type B Total transmission: With Rugate BS and Type A With Rugate BS and Type B With dielectric BS and Type A With dielectric BS and Type B

MCAO May 24-25, 2001MCAO Preliminary Design Review30 LGS WFS Transmittance Estimate Wavelength589nm Transmission per silvered reflection silvered reflections0.706 Science Beamsplitter net0.980 NGS/LGS Rugate beamsplitter0.990 NGS/LGS dichroic beamsplitter0.850 Air-glass per surface optimized 589nm element Zoom Lens Corrector0.984 Collimator,dielectric mirror0.998 Pupil Steering, dielectric mirror0.998 De-anamorphoser lens0.996 Shack-Hartmann Lens group (8 element) SH-CCD relay lens0.976 Total Transmission With Rugate BS0.65 With dichroic BS0.56

MCAO May 24-25, 2001MCAO Preliminary Design Review31 Optical Component Fabrication 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

MCAO May 24-25, 2001MCAO Preliminary Design Review32 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

MCAO May 24-25, 2001MCAO Preliminary Design Review33 PDR Agenda Thursday, 5/ Welcome 0805 Project overview 0830 Science case 0930 Break 0945 System overview 1015 System modeling 1100 AO Module optics 1145 Lunch 1245 AO Module mechanics 1340 AO Module electronics 1400 Break 1415 Beam Transfer Optics 1510 Laser Launch Telescope 1545 Closed committee session 1800 Adjourn