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

MCAOMCAO

Adaptive Optics ModuleAdaptive Optics Module Subsystem Optical Designs Subsystem Optical Designs

R.A.Buchroeder

May 24-25, 2001 MCAO Preliminary Design Review

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MCAOMCAO

MCAO Optical BenchMCAO 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


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MCAOMCAOScience path

LGS path

NGS path

Beam splitters

LGS focus

Science focus

NGS focus

Optical PathsOptical Paths


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MCAOMCAO

Parameter Science Path NGS WFS Path LGS WFS Path

Spectral passband, m

0.85-2.5

0.5-0.85 0.589

Field-of-view 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 m (0.002)0.010 for 1.25+/-0.1 m (0.0039)0.013 for 1.65+/-0.1 m (0.0019)0.018 for 2.20+/-0.2 m (0.0023)

0.05

NA

AO Module Optical AO Module Optical Design Design RequirementsRequirements


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MCAOMCAO

AO Module Science AO Module Science PathPath


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MCAOMCAO

H-band RMS wavefront errorH-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


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MCAOMCAOScience Path: I-band w/o Science Path: I-band w/o ADCADC

Circle = 0.053 arc sec


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MCAOMCAOScience Path: I-band at Z = 45 Science Path: I-band at Z = 45 degdeg



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MCAOMCAOScience Path: J band @ Z=45 Science Path: J band @ Z=45 degdeg



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MCAOMCAO

Science Path: H-band Spot Science Path: H-band Spot DiagramsDiagrams

• 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


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MCAOMCAOScience Path: K-band at Z=65 Science Path: K-band at Z=65 degdeg



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MCAOMCAOH-band Mapping error H-band Mapping error @ @ 45 degree Zenith Angle 45 degree Zenith Angle

Maximum distortion: 1.9%


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MCAOMCAO

Science Path ADC Science Path ADC @ Maximum Correction@ Maximum Correction

• I-band (0.78- 0.92 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


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MCAOMCAO

NGS Path Optical NGS Path Optical LayoutLayout


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MCAOMCAO

NGS Path Image Quality NGS Path Image Quality

• @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

Circle ~ 0.04 arc sec


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MCAOMCAO

NGS Image NGS Image MappingMapping

• Varies slightly with zenith angle

• Shown here at 45-degree zenith angle

• 1.3% distortion typical


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MCAOMCAO

NGS WFS Design ConceptNGS WFS Design Concept


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MCAOMCAOLGS Path: General LGS Path: General RequirementsRequirements

• 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.


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MCAOMCAO

LGS Optical Path LayoutLGS Optical Path Layout


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MCAOMCAO

LGS “Zoom Optics”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


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MCAOMCAO

LGS Image Quality vs RangeLGS 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


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MCAOMCAOLGS: from Zoom Optics LGS: from Zoom Optics to to S-H Lenslet Array S-H Lenslet Array


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MCAOMCAO

LGS: Wavefront at S-H ArrayLGS: Wavefront at S-H Array

• Representative case

• Central laser star

• 127 km range


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MCAOMCAOLGS: Mapping of DM0 to SH LGS: Mapping of DM0 to SH PlanePlane

• 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


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MCAOMCAOLGS WFS: SH Focus to CCD LGS WFS: SH Focus to CCD RelayRelay

Adjustable relay reduces non-common path errors from 100 to below 10 nm RMS


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MCAOMCAO

LGS WFS Relay: variable LGS WFS Relay: variable magnification mode magnification mode

• Geometrical spot diagrams

• Results superimposed over magnification range

• Circles = Airy disc


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MCAOMCAO

LGS WFS: Relay Distortion LGS WFS: Relay Distortion


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MCAOMCAO

Diagnostic WFS Design ConceptDiagnostic 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 arc-sec in object space


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MCAOMCAONGS WFS Transmittance NGS WFS Transmittance EstimateEstimate

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

Total transmission:

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


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MCAOMCAOLGS WFS Transmittance LGS WFS Transmittance EstimateEstimate

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

Total Transmission

With Rugate BS 0.65

With dichroic BS 0.56


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MCAOMCAO

Optical Component FabricationOptical 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


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MCAOMCAO

AOM Optical Design SummaryAOM 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


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MCAOMCAO

PDR AgendaPDR Agenda

Thursday, 5/240800 Welcome 0805 Project overview 0830 Science case0930 Break0945 System overview1015 System modeling1100 AO Module optics1145 Lunch

1245 AO Module mechanics1340 AO Module electronics1400 Break1415 Beam Transfer Optics1510 Laser Launch

Telescope1545 Closed committee

session1800 Adjourn

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

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