AO Opto-mechanical System DesignStatus, Issues, and Plans

Don GavelUCO/Lick Observatory

(for the opto-mechanical design team)

Keck NGAO Team Meeting #12

December 13, 2007

Videoconference

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Outline

• Overview/Background• Project Status• Issues• Work to do

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)– 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)– 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• Weekly team meetings Oct-Dec

Started with separate subsystem meetings, ending with all-team meetings

• Documents sharing Twiki pagehttp://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/AOSystemDesign

• CAD drawing database (PDMWorks)

• Functional requirements database (Contour)

• Several iterations of optical layout1-tier and 2-tier options explored

• 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

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[ Chris Lockwood input ]

Surface count update

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LGS WFS Pickoff Approach

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Dichroic selection

• Dichroic #1: LGS pickoff589nm reflect, >600nm pass

• Dichroic #2: Selectable– 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

• 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

Residual dispersion of f/15 ZnSe linear ADC, 60 degree zenith angle

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ZnSe external transmission

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ZnSe f/45 linear ADC

• 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

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Two-glass linear ADC

• 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

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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 nmMitigation: interchangeable ADCs for <700nm operation

• OSIRIS feedRequirements 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 feedE-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.

• 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 3.2.3Summary

• 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 completionNeed 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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