Gemini Extreme AO Coronagraph Design Mid-term review

1. Gemini Extreme AOCoronagraph DesignMid-term review Anand Sivaramakrishnan, Russell Makidon, Rémi Soummer Space Telescope Science Institute Ben Oppenheimer (PI), Andrew Digby American Museum of Natural History James Lloyd Cornell University and with a little help from… Laurent Jolissaint Hertzberg Instituteof Astrophysics

2. Overview Review types of coronagraphs Band-limited coronagraphs, phase mask coronagraphs Apodized pupil Lyot coronagraphs, shaped pupil ‘coronagraphs’ Pupil reformatters Remarks on coronagraph choice Selection criteria used manufacturability proof of existence inner working distance chromaticity integration w/calibration system Details on 2 baseline selections Opto-mech design covered elsewhere Tolerancing Lyot Project ExAO/coronagraphy lessons learned Future work

3. A progression of Lyot coronagraphsas good as it gets to date 1.3” waffle PalAO 30’ spot Solar 6.5” spot Stellar diffraction-limited Hayward et al, Dekany et al. Lyot Kalas & Jewettt The Lyot Project first light March 2004 65-85% Strehl at H Oppenheimer et al.

4. Gemini Pupil 8.1 m dia 1.18 m secondary dia (obscuration?) 1 cm spider width (Hole in secondary looks at sky: not relevant for coronagraph design phase A except for thermal) Spider width/D = 1/ 800 Spiders treated differently in each design Modelling image plane stop well needs at least l/6D pixels - either huge FFTs or use Goertzel-Reinsch methods Phase A study: FFTs Assume Fourier optics good enough (in-lab confirmation to few e-7: Kasdin)

5. Possible coronagraph designs • Band-limited Lyot Coronagraph (BLC) (Kuchner & Traub) • Easy-to-understand theory, a TPF front-runner • Very low throughput with obscured apertures • Phase effects with dense FPM • Apodized Pupil Lyot Coronagraph (APLC) (Soummer & Aime) • Smaller FPM occulting stop than Lyot or BLC • Manufacturers identified • Uncertainty of material response to wide band • Shaped Pupil (SP) ‘Coronagraphs’ (Kasdin et al) • Prototypes, lab demos exist, also a TPF front-runner • Non-rotationally-symmetric PSF • Phase Mask Coronagraphs (4 quad, Dual Zone) • Small inner working distances • Manufacturability an issue • Guiding can be a major issue (4 quad) • Pupil Reformatting Coronagraphs (Guyon) • Small inner working distances • Manufacturability, alignment, cost are issues today

6. Preserve options with wheels(Schematic!) • Pupil wheel • 1.5 cm pupil dia • Apodized Pupil, Shaped Pupil, clear pupil • Image plane wheel • f/64 • Choice of stops (sl/D, SP orientation,…) • Lyot Pupil wheel (cryo) • Hand off to Science Instrument • Positioning issues • Absolute positioning • Repeatability/stability • Position sensing/active control • Rotation within a slot (pupil/field)

7. SFWFS Superb help from Laurent Jolissaint, including quasi-real-time PAOLA development to support SFWFS Power spectrum of phase (log stretch) 64 actuators across 8.1 m (Nact=64) 16 layer MK model - outer scale 30m - seeing of 1arcsec at 500nm - 16 layers wind Integration 0.5 ms Servo lag 1 ms 96% SR No scintillation, no static errors Direct PSF 96% SR (log stretch)

8. Apodized Pupil Lyot Coronagraph(Soummer & Aime, 2002, Soummer 2004 in prep.) One of 2 baseline designs Tailored for Gemini pupil Bandwidths up to 20%, or CH4 on/off Can accomodate pupil wander Can accommodate phase error ~ density Reverse the apodization current in laser industry Azimuthally symmetric PSF (modulo spiders) At least 3 possible fabrication methods INO laser optics house (shown) HEBS glass-style (JPL) 1.5 cm pupil possible Spot ~4.2l/D dia = 0”.175 Pictures from manufacturer’s web catalog

9. Apodized Pupil Questions • Surface quality • Off-the-shelf? • Custom polish? • Cement • matches refractive index? • IR properties? • CTE match? • ND effects • Uniformity • Effect on phase • Scatter • Spiders: BOE calculation for 1 cm Lyot Stop Spider • D ~ 8 m, stop size s ~ 4, spider width w = 1cm • Grey area: D/s wide, D long, sw/D field strength • contribution: 4sw2/pD2 = 8e-6 of unocculted PSF power • Within l/D by sl/D – all behind stop 1” or 2” offered in catalog Scale of sl/D image mask in pupil plane is D/s Diffracted light from spider Bright spider in Lyot pupil D

10. APLC PSFs(Soummer & Aime, 2002, Soummer 2004 in prep.) 25l/D center to edge 50l/D center to edge Spot 4l/D dia = 0”.175 , monochromatic PSF, l/8D image scale Residual speckle intensity = power spectrum of phase aberration in the absence of amplitude variations (Sivaramakrishnan et al. 2002 ApJL, Perrin et al. 2003 ApJ) 1.0e-6 contrast contour 1.0e-6 contrast contour DIRECT CORONAGRAPHIC 96% SR SFWFS from PAOLA DIRECT CORONAGRAPHIC No wavefront aberration

11. APLC radial plots The coronagraph is easy The AO is hard

12. Shaped Pupil ‘Coronagraph’(Kasdin et al 2004) One of 2 baseline designs Tailored for Gemini pupil No bandwidth limit Can tolerate pupil wander Prototypes from TPF activities exist fabrication not a worry (lithographic) accomodates spiders in the design itself ~1.5cm or larger pupil possible (at reasonable cost, today) Preferred direction of suppression Design criterion: 1e-7 suppression in ‘waist’ Width of bright PSF ~5l/D

13. SP PSF No wavefront aberration 1e-6 contour in green Waist for 1e-7 suppression ~5l/D dia 96% SR SFWFS from PAOLA 1e-6 contour out-of-panel 64l/D 128l/D 64l/D 128l/D Zoom out 96% SR SFWFS from PAOLA 1e-6 contour With image plane mask Zoom out 96% SR SFWFS from PAOLA 1e-6 contour Waist 5l/D dia = 0”.21 at H, monochromatic PSF, l/2D image scale Residual speckle intensity = power spectrum of phase aberration in the absence of amplitude variations

14. SP radial plots The coronagraph is easy The AO is hard

15. TBD – Tolerancing & understanding(APLC & SP, phase 1 as well as during construction) • Astrometry • Plate origin • Plate scale • Field distortion • Interaction w/Calibration system • Flexure • Chromaticity • Etc., etc. • ADC – like tip-tilt • Centering drift w/construction errors • Centering drift w/clocking errors • Refractive index/dispersion errors • Interaction w/NCP Calib system • Interaction w/Science camera • Interaction w/AO system, TCS • Flexure, chromaticity, stability • Pointing, header info, centering, defocus… • Optical Alignment, flexure • Response to “behind spot” aberrations • Response to “near spot edge” aberrations • Use eg defocus response for astrometry • Studies by Lloyd, Green, self, Soummer, exist • Vibration • Withstand vibration? • Request for less vibration? • Pupil Imaging • Uniformity of illumination, image distortion • Curvature of pupil image • Other aberrations of pupil image • Positioning in Z, tip/tilt • Mismatch w/Lyot pupil image • Occulting Image Stop • Edge irregularity • Positioning in Z (defocus), tip, tilt

16. Fully Functional ExAOC getting data now: Uses 941 Actuator AO system at AEOS (3.6 m Telescope, 11 cm subapertures) 1.6” AO control radius at H band Lyot-style coronagraph with hard-edged masks optimized with Sivaramakrishnan et al. (2001) method for Z, J, H bands Internal WFE <60nm rms, on-sky Strehls from 60-90% Pixel scale 15 mas ~ /6D at H band Focal Plane Masks made from glass, steel, nickel, nickel over steel to find best solution http://lyot.org

18. Reflective Masks: Pupil is imaged continuously during observations

19. Prototype Focal Plane Mask 334 microns Microscope Image by Jacob Mey and Charlie Mandeville (AMNH EPS Microprobe Lab)

20. Science Grade Mask 334 microns Microscope Image by Jacob Mey and Charlie Mandeville (AMNH EPS Microprobe Lab)

21. Confocal Microscopy Red, Green or Blue laser Can resolve features at /10 (0.05 m min)

22. Confocal Microscopy Red, Green or Blue laser Can resolve features at /10 (0.05 m min)

23. Lessons Learned from Masks Structure in the FPM larger than about /4, or 250 nm at 1 micron results in detectable corruption of the coronagraph’s dynamic range ExAOC for Gemini will require significantly finer focal plane masks. We plan to assess this quantitatively by middle of next summer. AMNH can measure features as small as .1 micron with confocal microscopy and possibly at the nm level with SEM, depending on destruction of sample.

24. In Lab Performance Total Wave Front Error: 32 nm (8 optics) Unocculted Lab Star Pupil 98.7% Strehl at H band (1.6 microns) Hubble’s last IR instrument had 92% Strehl at H Band ~65 nm RMS WFE

25. The Raw Data 1 minute H band exposure of 55 Cancri. Pixel scale is 15.35 mas/pixel

26. Unocculted Image S ~ 80-90% Core: .2 s Wing: 2 s 3” unocculted H band image of delta Hercules ( V = 3 mag. A3IV, 25 pc)

27. PSFs Ideal Image Ideal Pupil Best Possible Real Image Real Pupil

28. PSFs 2 Ideal Coronagraph Pupil Ideal Unocculted Image REAL DATA! Real data! Real Coronagraphic Pupil Best Unocculted Image

29. 55 Cancri 6.5” Occulted by 334 mas mask H-Band 1 minute Exposure

30. Cujam

31. Delta Hercules H band 5” FOV 150 20 sec images Scintillation ~10% (I) H = 11 mag at .3” in single exposure AO Issues limit us but most will be fixed by January

32. ExAO movieThis is NOT a simulation Lyot Project data: 10 s exposures, 200 exposures

33. IFU w/APLCThis is a simulation (Soummer)90% Strehl ratioSpeckles move in position, apparent companion stays fixed

34. Lyot Project Data in Perspective 6” Hubble WFPC2 I band 1995 Gliese 105AC Palomar 60” JHU AOC Coronagraph I band 1994 Gliese 105AC Palomar 200” AO Coronagraph K-Band 1999 Gliese 105AC Lyot Project H-band 2004 55 Cancri

35. Other question(APLC & SP, phase 1 as well as during construction) • Scintillation • Roberts’ Lyot Project I-band video-rate data on AEOS • Early Lyot results (Siv., Perrin, et al) • Quasi-static I-band SR 97% • At video rate I-band: ‘fast’ SR ~97% • Do Gemini scintillation data exist? • Mirror surface degradation • Gemini M1, M2 reflectivity (in situ) would be useful • Behaviour with time? • Effect of scatter on dynamic range • Reduction strategies • Baffling

36. Conclusion • Two non-scary inexpensive baseline designs chosen • But get the details right • Keep ancillary science goals in mind • AO limits the science more than coronagraph • Study science payoff vs Inner working Angle • Cost, complexity, scarier designs • Understand spiders better • Use data reduction, observing strategy • Reduce $$$ • Increase search area