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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