Keck Next Generation Adaptive Optics Team Meeting 6 1 Optical Relay and Field Rotation (WBS , ) Brian Bauman April 26, 2007

Keck Next Generation Adaptive Optics Team Meeting 6 2 Status Designs for narrow-field (30”) and wide (100”) AO relays Designs for MOAO and TTFA arms Designs for WFS package WFS split/pickoff options explored Field rotation options explored

Keck Next Generation Adaptive Optics Team Meeting 6 3 Narrow field reflective design 25 mm MEMS, 30” field diameter Requires ~18° OAP Generates sizable pupil distortion/tilt

Keck Next Generation Adaptive Optics Team Meeting 6 4

5 Narrow field on-axis design All-refractive design Narrow field, 30” diameter Passes LGS, enables “closed loop” high-order WF control MEMS DMs (25 mm pupil) MCAO option: Second optical space for 2 nd DM. TT stars picked off at front focal plane for sky coverage (wider TT field), => open loop TT sensing. Steer additional LGS to TTStars on technical field?

Keck Next Generation Adaptive Optics Team Meeting 6 6 On-axis refractive relay 380mm Focal plane 30 arcsec diameter MEMS DM (25 mm)

Keck Next Generation Adaptive Optics Team Meeting 6 7 On-axis AO field-dependent aberrations (but pessimistic because there is no refocusing with λ) Diffraction-limited in V band 15 arcsec

Keck Next Generation Adaptive Optics Team Meeting 6 8 Performance over H-band

Keck Next Generation Adaptive Optics Team Meeting 6 9 On-axis AO field-dependent aberrations to LGS 2.5 at edge of field, P-V ray deflection (WF slope) of 0.15”, mostly astigmatism and coma. –Known as a function of field and zenith angle –Within dynamic range of radial CCD WFS –Easily correctable with a MEMS, or use static corrector + WFS offsets

Keck Next Generation Adaptive Optics Team Meeting 6 10 On-axis AO field-dependent pupil distortions <43 micron displacement of a marginal ray at =1.25  the edge of the field, <0.1 subaps (430 micron act spacing MEMS) <22 micron displacement as a function of =  over all field angles

Keck Next Generation Adaptive Optics Team Meeting 6 11 Issues with refractive design Chromatic aberration across band Inhomogeneity –Spec at 10^-6, glass thickness ~5mm => ~1.3 nm rms OPD variation/optic –Probably not a problem Transmission/coatings: probably get % per surface for nm; need to check for visible Birefringence –Glass spec birefringence 0.2nm rms/optic –Probably not a problem (except possibly ExAO)

Keck Next Generation Adaptive Optics Team Meeting 6 12 Wide field relay design 100 arcsec diameter field All refractive design Diffraction-limited at R band (<0.07 ) over the entire field. Assumes correction of spherical. Pupil distortion: Chief ray shifts 770 microns = 2 subapertures, tolerable? LGS sees 15 of coma and astigmatism, ~1.0” of ray deflection –Challenges the WFS dynamic range (knowable, can be open-loop corrected)

Keck Next Generation Adaptive Optics Team Meeting 6 13 Wide field relay 390 mm 80 mm (100 arcsec) field 25 mm MEMS

Keck Next Generation Adaptive Optics Team Meeting 6 14 Wide field relay – field dependent aberrations 50 arcsec

Keck Next Generation Adaptive Optics Team Meeting 6 15 Performance over H-band

Keck Next Generation Adaptive Optics Team Meeting 6 16 Wide field relay design More difficult with small DM due to pupil distortion The “slippery slope” of wide field closed-loop design: –Is the wider field science driven? Or is it just to correct TT stars? –Would need more lasers to reduce tomography error –Would need more conjugate DMs to reduce gen. anisoplanatism

Keck Next Generation Adaptive Optics Team Meeting 6 17 c) DMs at 0,5,10 km b) DMs at 0,10 km a) DM at 0 km Generalized anisoplanatism as a function of field angle on the KNGAO standard (r 0 =15.6cm  0 =3 arcsec) atmosphere, from KAON 452 Different field angle optimizations

Keck Next Generation Adaptive Optics Team Meeting 6 18 MOAO relay design Appropriate to MOS science arms and LOWFS Reflective design, off-axis ellipse MEMS 500mm MEMS File: “IRMOS, 2 arcsec field, 10mm woofer first, 60mm DM second, up to dewar window, with apertures.SES”

Keck Next Generation Adaptive Optics Team Meeting 6 19 LGS WFS Closed loop architecture: standard Hartmann lenslet WFS design at AO relay output. –On-axis AO relay is low enough aberration so no variable optics needed, other than focus motion. –Two DM MCAO is needed to correct LGS over the field, otherwise it’s open-loop sensing (but closed loop on the DM) Open loop architecture: use MEMS correctors in SHWFS. –Simple refractive or reflective relay –Pupil reimage to lenslet only; 2 nd pupil reimage not needed for DM because of narrow field –Mechanical focus motion

Keck Next Generation Adaptive Optics Team Meeting 6 20 Wide field LGS WFS system from TMT IRMOS design

Keck Next Generation Adaptive Optics Team Meeting 6 21 Wide field LGS WFS system DMs

Keck Next Generation Adaptive Optics Team Meeting 6 22 Field Rotation – Narrow Field AO We have a K-mirror design from the Indian Wells meeting that is 500 mm behind focus and handles 1 arcmin field –Narrow field AO only has 300 mm available, so need rotator ahead of focus. How much space is available ahead of Keck focus? K mirrors are small on a narrow field –30 arcsec field: fits in 200 mm, 65 mm high, sucks in focus by ~200 mm Conclusion: K mirrors may be feasible for narrow field AO designs Option: tumble AO+instrument

Keck Next Generation Adaptive Optics Team Meeting 6 23 Field Rotation – Wide Field AO Recommend MOAO IFU on a upward or downward-looking turret barrel At most 250mm difference between 90 km and infinity focus. May need relay optics into WFS (first optic on a rotating wheel).

Keck Next Generation Adaptive Optics Team Meeting 6 24 Conclusions Small refractive on-axis AO design approach eliminates pupil distortion and LGS aberration problems Wider field design is hard with 25mm MEMS limitation. Relaxed with larger (60 mm) DM. Consider drivers for wide field system. Is TT star pickoff the only issue? MOAO reflective relay designs carried over from TMT/IRMOS study Several field rotation options presented, depending on field size and space available ahead of focus