1. 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

2. 2 Outline Overview/Background Project Status Issues Work to do

3. 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) –1 st order designs –Requirements Database (FRD) entries –Design report / input to System Design Manual –Descoped: ICD drafts, costing 3

4. Opto-mechanical design status Weekly team meetings Oct-Dec Started with separate subsystem meetings, ending with all-team meetings Documents sharing Twiki page http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/AOSystemDesign CAD drawing database (PDMWorks) Functional requirements database (Contour) Several iterations of optical layout 1-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 4

5. AO relays layout 5

6. Placement of Instruments 6 [ Chris Lockwood input ]

7. Surface count update 7

8. LGS WFS Pickoff Approach 8

9. Dichroic selection Dichroic #1: LGS pickoff 589nm 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 9

10. NGAO Passband Definitions KAON 530 10

11. Atmospheric Dispersion Correctors

12. 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 12

13. ZnSe external transmission 13

14. ZnSe f/45 linear ADC Better performing and can be made shorter because of slow beam (100 mm long in this example) 14

15. 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) 15

16. S-NPH2 / S-BAL42 transmission (excludes coating losses) 16

17. 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. 17

18. 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 18

19. 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 19

20. 1-tier layout 20

21. 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 21

22. 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 22