Feasibility studies for the MOBIE Acquisition, Guiding, and Wavefront Sensing (AGWFS) subsystem Hu Zhongwen , Chen Yi,et al. (NIAOT) Zhu Qingfeng, Zhai Chao,et al. (USTC) May 25, 2011 04/09/2011 TMT.INS 1 1 1 1 1

Outline Introduction of MOBIE Top-level requirements of AGWFS subsystem Project Team & Schedule Feasibility studies

WFOS Requirements vs. MOBIE Design Requirements/goals Realized in MOBIE concept Wavelength range: 0.31 –1.0µm 0.30 – 1.1µm Field of view: >40.5 arcmin2 40.3 arcmin2 (4.2’ x 9.6’) Total slit length ≥ 500 576 (9.6 arcmin) Image quality: – fwhm ≤ 0.2 (imaging) 0.1µm band < 0.2” – fwhm ≤ 0.2 (spec) any , no re-focus < 0.2 (preserve resolution) Spectral resolution: – 1000 < R < 5000 for 0.75 slit R = ~1000, ~5000, ~8000 – Complete -coverage at R~1000 complete or select orders Throughput ≥ 30% (all ) > 40% down to 0.30 µm (est.) Sensitivity: limited by photon stats for t>300s (high transmission design) Field acq: <3 min/mask, <1min/single obj. (addressed in CDP) 01/19/2011 01/19/2011 3 3 3 TMT.INS.PRE.11.008.REL01 3 3

MOBIE Design Concept - Optical Two color channels, each with direct imaging and three spectroscopic modes TMT FOCAL SURFACE & MOBIE SLIT MASK (~550 x ~1250 mm) RED FOLD COLLIMATOR (~1m x ~1.8m) DICHROIC RED DETECTOR BLUE DETECTOR RED CAMERA BLUE CAMERA GRATINGS X-DISPERSION PRISMS 01/19/2011 01/19/2011 4 TMT.INS.PRE.11.008.REL01 4 4 4 4

MOBIE Design Concept - Mechanical STRUCTURE ENCLOSURE ADC CABLE WRAP CARRIAGE COLLIMATOR 01/19/2011 01/19/2011 5 TMT.INS.PRE.11.008.REL01 5 5 5 5

MOBIE on TMT 01/19/2011 01/19/2011 6 6 6 TMT.INS.PRE.11.008.REL01 6 6

Functionality of MOBIE AGWFS subsystem Acquisition Check the telescope pointing Guiding Maintain a stable telescope tracking Nodding Wavefront sensing Low-order wavefront error correction Acquisition & Guiding can be performed by the same camera, they are different only in term of function/mode. Acquisition mode is only used for checking the telescope pointing. Open-loop Guiding could be both open-loop or close-loop. In the close-loop, the guiding star should always be in the guiding field.

Top-Level Requirements Acquisition (mainly required for TMT early operations) : 20 arc sec diameter FoV Guiding: 0.5 Hz closed optical guide loop bandwidth  5 Hz guider frame rate To meet the overall requirement of 0.05 arc sec (rms) image position uncertainty Allocation for guiding is 10 mas (rms) for guide error, or PSSN=0.999 Support nodding and offset: 1 [10] arc sec nods along slits in 10 [20] seconds with 80% duty cycle 30 arc sec offsets maximum (in any direction) Wavefront sensing: 30 s typical exposure time Degrade telescope point source sensitivity (PSSN) by at most 0.9960 Unaveraged turbulence contributes a factor of 0.9965 after 300 seconds Remaining factor of 0.9995 corresponds to 75 nm RMS WFE Sky coverage (Relaxed, FOV 3 sq arcmin) 95% for galactic pole guide star densities Must be split into 97.5% for guider and for AO WFS if separate stars are used Given the design requirements below the limiting star magnitude for the guider to achieve the 50 mas measurement error at 5Hz is mV~=23.6 (TBR). This value is in fairly good agreement with the MOBIE OCDD value of mV=23. The OCDD analysis assumed 10-second integration times with “bright moon” conditions. This analysis used a 5Hz integration time and a background of 20.65mV/arcsec2. Conversion from image jitter (guide error) to PSSN: PSSN ~= 1 – alpha*sigma^2; while sigma is the RMS jitter in mas and alpha is a coefficient of 9.12e-6. PSSN describes the photometric efficiency of the system.

Project team NIAOT(Nanjing Institute of Astronomical Optics & Technology) : Hu Zhongwen, Chen Yi , Wang Jianing ,Dai Songxing , Hou Yonghui ,Tan Zheng USTC(University of Science and Technology of China): Zhu Qingfeng, Zhai Chao, Liu Zhigan NAOC(National Astronomical Observatories) UCSC(University of California, Santa Cruz) ： Bruce Biglow 2019/4/6 04/06/2011

Schedule of the Phase 2019/4/6 04/06/2011

Main issue & objective for feasibility study Explore all potential solutions Demonstrate potential possibilities Detect possible problems Doing first-order trade-offs Find near optimized solutions instead of going deep into design So would not “lose the way” Solutions should be applicable & versatile Simple & applicable Leave variations for further optimization

FOV complexity Inside FOV of ADC & TMT Outside FOV of MOBIE Preserve space for GLAO WFS Avoid collision – best outside slit mask robot region,possible collision with spectrograph camera. Perform Acquisition,guiding & wavefront sensor function

Structure space Complexity

Optics complexity Option 1: large optics Fixed imaging sensor(s) for acquisition and guiding Patrolling wavefront sensor Option 1a: two suits of patrolling mechanics Patrolling imaging sensor for acquisition and guiding Option 2: large optics Fixed imaging sensor for acquisition Patrolling wavefront sensor and separate guider, splitting the light from a single star Option 3: Need more investigation Patrolling wavefront sensing provides both wavefront sensing and guiding functions Additionally, either a Shack-Hartmann wavefront sensor or a curvature wavefront sensor could be considered for the wavefront sensing function

Summery of the work done 1. Explore shared FOV concept Preserve or even make better top-level performance Relax optics complexity: X large expensive optics Relax FOV complexity: X crowded FOV Reduce structure complexity 2. Explore flexible & eliminate improper patrolling schemes Explore a few optically available schemes to relax mechanical complexity: X possibility of collision Need further feasibility investigation & iterative work with MOBIE structure considerations especially the ADC and the red camera. 3.Perform a specific optical design It works from optical point of view Need further evaluation

Pre-assumed concept -- need to explore new possibilities C-Option1 : Multi-FOV concept Very large optics Crowded FOVs Large space required

Explore Shared FOV concept Does not lose sky coverage Make available larger FOV for both guider & wavefront sensor Other Merits More FOV vacant Share part of the optics between guider & wavefront sensor Share patrolling scheme: might be a defect Optics small & compact *** Reduced FOV / Optics/ structure complexity

Structure Space near MOBIE focal plane 150 mm 1850 mm 700 mm

Focal plane optics & mechanically available IFOV

Shared FOV concept with virtual patrolling schemes C-Option 2: patrol 2-D together with small IFOV of the guider, optics small. Available FOV is the largest. Pupil distorsion is the least. C-Option 3: patrol 1-D together + Wavefront sensor patrol 1-D , optics larger. Pupil distorsion >1%. Available FOV limited.

C-Option 3: 1-D patrolling of wavefront sensor Remark: C-Option 3 still could be used if with special petrolling scheme .

Explore patrolling schemes -- Patrolling scheme 1 Remarks: A cocentric design is considered before to achieve rotation symetry. It is abandoned to make optics simple.

FOV strategy(off-axis distance) --Rotation angle issue Larger perpendicular range / far off-axis configuration --Compromise the restrictions of mechanical space available

Patrolling scheme 2 Field mirror -> telecentric design 1-D movement of M1 + Refocus of CCD instead of rotating of the detection unit ---for“perpendicular patrolling” Remarks: 2-D patrolling of M1 is possible (No other movements)

Patrolling scheme 3 Rotate mirror-pairs instead of rotating of the detection unit: ---for“perpendicular patrolling” 2019/4/6 04/06/2011

Possible image quality (Scheme 1 without refocus) Colimator : Triplet Camera: CANNON Lens array: AOA(only for guider) Patrolling scheme 1 Box size 0.1” IFOV: 22”

Patrol position near axis (Without Retune-focus)

Patrol position near edge of FOV (Without Retune-focus)

Realistic Optics : layout

Re-designed Colimator -- All spherical lens surface

guider parameters F: 107396 ; F/#: 3.61 IFOV: 21” 0.52mm/1” Remark: it is know that : FOV 3’ or larger could be achieved by patrolling with small IFOV

guider image quality

Wavefront sensor parameters F: 130000; F/#: 4.35 ; 0.63mm/” IFOV: 7.2” ; field stop 3”;; efficiency 42% Lenslet array: 7x7SUSS38-5103-109-121, 1015μm ,100mm Remark: With required 3” IFOV, these design makes available patrolling +/- 2.1” (field stop move)

Wavefront sensor full aperture image quality

Better image quality with smaller IFOV (3.6”)

Pre-selected CCD

Mechanical Concept 2019/4/6 04/06/2011

Comments AGWFS is a small complex system It has interfaces with spectrograph and has feedback to telescope control. It can help to achieve ultimate performance It should be well designed and evaluated to meet the top level requirements(There are difficulties: off-axis WFS, Large Science FOV, magnitude & accuracy ) Cost effective 2019/4/6 04/06/2011

Thanks ! Thanks : Brent, Bruce, Rick, Rebecca for Efficient Collaborative work Jerry, Chuck, Mark, George, Luc,… for video/email discussion Mitch for his previous work on requirements & his previous options idea TMT office UCSC HIA