AO Opto-mechanical System Design
Status, Issues, and Plans
Don Gavel
UCO/Lick Observatory
(for the opto-mechanical design team)
Keck NGAO Team Meeting #12
December 13, 2007
Videoconference
Outline
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Overview/Background
Project Status
Issues
Work to do
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Overview of NGAO Design Effort
• Architecture: Cascaded Relay
Decision at July architecture retreat – KAON 429
Characterized by woofer-tweeter arrangement, with woofer in closed loop
• Divided into subsystem efforts (kickoff in August)
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Enclosure
AO Opto-mechanical
AO Wavefront Sensors
AO Operational Tools
Laser
Laser Facility
Controls
• Inputs: (common)
– SRD, Rainbow Chart, initial FRDs, KAON 429, Error Budgets
• Outputs (common)
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1st order designs
Requirements Database (FRD) entries
Design report / input to System Design Manual
Descoped: ICD drafts, costing
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Opto-mechanical design status
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Weekly team meetings Oct-Dec
Started with separate subsystem meetings, ending with all-team meetings
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Documents sharing Twiki page
http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/AOSystemDesign
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CAD drawing database (PDMWorks)
Functional requirements database (Contour)
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Several iterations of optical layout
1-tier and 2-tier options explored
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Field de-rotator
First cut on instrument volumes
ADCs
Dichroic suite. Dichroic exchange mechanisms
Pickoff mechanism options (separately considered for LGS, HOWFS)
Acquisition schemes
Calibration tools
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AO relays layout
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Placement of Instruments
[ Chris Lockwood input ]
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Surface count update
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LGS WFS Pickoff Approach
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Dichroic selection
• Dichroic #1: LGS pickoff
589nm reflect, >600nm pass
• Dichroic #2: Selectable
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None – NGS AO mode
Mirror – to d-NIRI & LOWFS
J+H reflect, K transmit – K band narrow field science
J reflect, H+K transmit – H band narrow field science
H reflect, J transmit – J band narrow field science
IR reflect, Vis transmit – Visible narrow field science
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NGAO Passband Definitions
KAON 530
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Atmospheric Dispersion Correctors
ZnSe linear ADC
Residual dispersion of f/15 ZnSe linear ADC,
60 degree zenith angle
180
160
Residual dispersion (milliarcsec)
• Plots are for 60° zenith angle
• < 10 mas residual dispersion
for λ=0.9-2.5μ
• ZnSe transmission starts
rolling off at 0.7 μ (external
transmission shown; losses in
flat region are almost entirely
due to Fresnel reflection)
• <40nm rms for λ=0.9-2.5μ
• ~160 mm long, but could be
made shorter if necessary
• Availability larger than 4.5-5”
would be problematic right
now, but II-VI’s new plant
comes online in the next few
months
140
120
100
Series1
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60
40
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-20
0.6
0.8
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1.2
1.4
1.6
1.8
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2.2
2.4
wavelength (microns)
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ZnSe external transmission
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ZnSe f/45 linear ADC
180
160
Residual dispersion (milliarcsec)
• Better performing and
can be made shorter
because of slow
beam (100 mm long
in this example)
Residual dispersion of f/15 ZnSe linear ADC,
60 degree zenith angle
140
120
100
80
Series1
60
40
20
0
0.6
0.8
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1.2
1.4
1.6
1.8
2
2.2
2.4
-20
wavelength (microns)
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Two-glass linear ADC
180
160
Residual dispersion (milliarcsec)
• Generally better
correction over wider
band, but at cost of
transmission (extra
surfaces and perhaps
transmission loss in
visible and/or K-band,
depending on glasses
chosen)
Residual dispersion of f/15 S-NPH2/S-BAL42 linear ADC,
60 degree zenith angle
140
120
100
80
Series1
60
40
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0.6
0.8
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1.2
1.4
1.6
1.8
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2.2
2.4
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wavelength (microns)
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S-NPH2 / S-BAL42 transmission
(excludes coating losses)
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Visible light (0.7-0.9) f/45 linear
ADC
• Not started, but narrow band, small field, and slow beam should
make this not very hard.
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ADC Summary
• All linear ADC’s should be possible in 200mm or
less length
• Linear ADC’s over 0.9-2.4 μ (at f/15 or f/45) are
straightforward with single glass
• Linear ADC’s over 0.7-0.9 μ possible with one
glass with rolloff at 0.7 μ, or with two glasses
(perhaps with rolloff at K-band); other glass
choices should be investigated
• Linear ADC over 0.7-0.9 μ not started, but
should be straightforward
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Opto-mechanical design: Issues
• ADC passband: ZnSe glass falls off <700 nm
Mitigation: interchangeable ADCs for <700nm operation
• OSIRIS feed
Requirements needed
– High order vs low order correction (f/46.5 feed vs f/15 feed)
– Beam reformatting: match present f/15 or correct for internal pupil mismatch
Large footprint
– Accommodated if OSIRIS is a temporary substitute, rather than in addition to,
NGAO-matched narrow field NIFS
• Interferometer feed
E-field orientation match
S-P amplitude match
– Study underway
– Fallback option: layout that duplicates present AO system reflections, incidence
angles, and coatings – “1-tier” design
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1-tier layout
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3.2.3 AO Opto-mechanical design deliverables
 First order optical design
 Mechanical drawings showing layout of optical bench, support
structure, optical elements, and interfaces to instruments, tip/tilt
sensors (DNIRI), and wavefront sensor package.
• Written description of the design.
– preliminary performance and tolerance analysis results
– plan for comprehensive performance analysis
– first assessment of high risk items.
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Preliminary cost analysis.
Inputs to the preliminary design phase work breakdown structure
Inputs to appropriate sections of FRD version 2
Inputs to the System Design Manual
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Opto-mechanical Design 3.2.3
Summary
• Work remaining
– Complete requirements entry process
– Summary write-up for SDM
– Completion of enclosure design
– Completion of visible ADC design
• Time required to completion
~2 weeks
• Cost/Resources to completion
Need input on hours spent to date from team members
Approx. 80 person-hrs needed to complete (10% of plan)
assumption: someone available to assist Contour data entry from spreadsheets
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