Design of the NFIRAOS PWFS module Jean-Pierre Véran National Research Council Canada – Herzberg, Victoria, BC Presentation at the "Wave Front Sensing in the ELT era" workshop Padova - Oct 2, 2017 TMT.AOS.PRE.17.XXX.REL01

NFIRAOS Simplified Control Diagram in LGS Mode WFS/DM telemetry (PSF recon) Telescope offloads TWFS is an NGS WFS that measures radial modes at low speed to track changes in the profile of the sodium layer. It is nominally a ~12x12 WFS. Also track drifts in NCPA compensation? Reconstruction parameters RTC Param. Gen. RTC Star selection mechanism LGS Offsets Truth WFS LGS Pixels DM/WFS Statistics Actuator commands OAP LGS Trombone LGS BS 6 LGS WFS 6 LGS WFS OAP OIWFS Pixels On Inst. WFS(s) 6 LGS Inst. Fold Inst. Fold NGS(s) Sci. Obj. OAP DM11 OAP OAP DM0 + TTS SCI BS OAP To Sci. Instrument

NFIRAOS Simplified Control Diagram in NGS Mode WFS/DM telemetry (PSF recon) Telescope offloads NGS WFS is a high-order WFS. This mode is typically used for high-contrast imaging, or when the lasers are not available. Reconstruction parameters RTC Param. Gen. RTC Star selection mechanism NGS WFS pixels NGS WFS DM/WFS Statistics Actuator commands OAP LGS BS OAP OIWFS Pixels On Inst. WFS(s) Inst. Fold Inst. Fold NGS(s) Sci. Obj. OAP DM11 OAP OAP DM0 + TTS SCI BS OAP To Sci. Instrument

Context within NFIRAOS Input window SS- Source simulator Rotating pupil mask OAP3 DM11 OAP1 OAP4-S OAP4-L OAP2 VNW- Visible natural wavefront sensor Instrument selection mirror Beamsplitters Tip-tilt stage & DM0 LGS- Laser wavefront sensors & trombone OAP4-V

PWFS top-level parameters CCID-96 256x256 pixels frame transfer CCD with 64 output amplifiers <3e- noise at 800 Hz frame rate On-chip binning Each pupil image has 96 pixels in diameter Oversamples 60x60 Fried geometry Binning to 48, 24, 12 and 6 possible PWFS module design sub-contracted to ABB and INO (Quebec City, Canada) PDR: October 2017 FDR: March 2018 NFIRAOS FDR: June 2018 TMT.AOS.PRE.15.039.DRF02

Current CAD model

Double Pyramid Canadian and Italian double pyramids have same optical effects Italian pyramid already prototyped for GMT Canadian pyramid has better thermal properties NFIRAOS operates at -30C so ΔT=50C !

Can we use a single pyramid? PWFS operates between 610nm and 785nm Chromatic blurring with single pyramid ~0.9 pixel Assumes BK7 Current budget for quality of pupil image is ~0.9 pixel FWHM Dominated by charge diffusion (0.7 pixel FWHM) Double roof-prism set-up at NRC (Van Kooten 2016)

Relaxation of quality of pyramid edges and roof Original specification: Edge and roof < 5um We have simulated the effect of having a 22um edge / roof f/45 beam on pyramid Incremental wavefront error is only 16nm RMS Specifying edge / roof < 20um makes pyramid much easier to manufacture

Relaxation angle tolorances on pyramid (Lardiere AO4ELT4) Wang, L, AO4ELT4 2017

-30C operated mechanisms Rotary stage (ADC) customized version of PI stage DT-80 Slow tip, tilt and focus stage (pupil pointing) customized version of PI stage PLS-85 (linear stage) PI S330.8 (tip-tilt) Required to achieve repeatability spec (<5 urad) Fast Steering Mirror X-Y stages customized version of PI stage LS-180 Main challenge are: Travel: 300mm Bi-directional repeatability: 2um Differential accuracy: 4um over 60mm (2mas over 30” on sky for AO guider offsetting) and 20um over whole travel range

FSM trade-off Traditional choice for PWFS modulation: PI S330 However, this module has several downsides: Heat dissipation (~4W when modulating at 800Hz) Would require active cooling Lifetime (109 cycles or about 4 months at 800Hz @ 1000 hours/year) PI has proposed a custom mono-crystal stage No heat dissipation Improved lifetime (to be quantified) Very linear (no capacitive sensor, no feedback electronics) But limited stroke: ≤±0.3mrad or 10λ/D (at all frequencies)

Testing of mechanisms PI has been the most responsive / interested vendor PI mechanisms are rated to -20C PI will test the mechanisms at room temperature and at -30C No optical test We are in the process of procuring all mechanisms now to conduct our own optical tests at -30C

TMT Pupil Mask NFIRAOS on Nasmith platform and does not have a derotator Telescope pupil will rotate on DMs and WFSs For calibration and testing, a rotating pupil mask could be implemented at an image of the telescope pupil in the high-altitude DM (DM11) relay Could simulate ragged pupil edge and spiders Would have to retract during operations If no pupil mask, pupil is defined by oversized circular mask on DM0

Interaction matrix calibration For LGS WFS, we are planning to use a hybrid approach Experimental interaction matrix to derive low-order mis-registration parameters. Then the actual interaction matrix is computed analytically, including details of TMT pupils. Interaction matrix and reconstructor are updated as the TMT pupil rotates (every 0.5 degree) Can this approach work for PWFS, or do we need to use an experimental interaction matrix In order to properly capture diffraction effects In the coming months, we are planning to compare experimental and synthetic interaction matrices on our PWFS bench