High Contrast Imaging with FocalPlane Wavefront Sensing and PIAA for Subaru Telescopes

Olivier Guyon (guyon@naoj.org)Basile Gallet (gallet@naoj.org)Eugene Pluzhnik (pea@naoj.org)Hideki Takami (takami@naoj.org)Shinichiro TakanaSubaru Telescope / National Astronomical Observatory of Japan

Motohide TamuraLyu AbeNational Astronomical Observatory of Japan

Subaru AO team & HiCIAO team

Introduction / Outline

Goal: high contrast at low inner working angle (IWA)

Half the IWA = 8x more accessible planets0.1'' – 0.2'' has 7x more planets than >0.2''lots of science possible with ~1k actuators

Reflected light from closeby planets is strongerat ~0.1''-0.2'', 1e8 contrast for some RV planets

High-contrast AO at Subaru Telescope

AO188188 elementscurvature system(first light: end 2006)

HiCIAOdifferentialimagingnear-IR camera(2007)

''Tweeter'' + low IWAcoronagraph

Nasmyth focusflexible & friendlyenvironment

PIAA

PIAA / APLC Hybrid coronagraph

Angular separation

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Why focal plane wavefront sensing ?''What you see is exactly what you want to remove''

Main sources of wavefront errors :- Photon noise- Time lag- Fitting errors

# of elementsAliasing

- Non-common path errorsoptical components (static)actuator vs. WFS registration (static & dynamic)

- scintillation- wavefront chromaticity

refraction index of air (OPD chromaticity)Fresnel propagation (OPD and ampl. Chromaticity)chromatic shear of wavefront

''fundamental'' contrast limitations of AO with vis. WFS & near-IR imaging

8m telesc.V WFSH imaging

(Guyon, 2005)

Wavefront sensors ''efficiencies'' (Guyon 2005)

Square root of # of photons required to reachfixed sensingaccuracy

plotted here forphase aberrationsonly.

''Dark Hole'' DM control

If wavefront is known,DM can be controlledto ''perfectly'' cancel speckles

JPL High contrastimaging testbed

Malbet, Yu & Shao (1995)Guyon (2005)Give'on (2003-2006)Borde & Traub (2006)

Fast(er) algorithm using linear approximations – few mson single CPU, code not optimized for speed

PIAA coronagraph development at Subaruco-funded by JPL and Subaru/NAOJ

Utilizes lossless beam apodization with aspheric optics(mirrors or lenses) to concentrate starlight is single diffractionpeak (no Airy rings).

- high contrast- Nearly 100% throughput- IWA < 2 l/d- 100% search area- no loss in angular resol.- can remove central obsc.and spiders- achromatic (with mirrors)

For Subaru, Lyot Coronagraph with PIAA- apodized inputpupil. IWA ~ 1 lambda/d

Early demonstration in lab

(Galicher et al. 2005)

Lenses made byMasashi Otsubo (ATC, NAOJ)

PIAA mirror units (Axsys)JPL-funded TPF-C technology development

32x32 MEMs DM is used for FPAO test in lab with PIAA coronagraph

One of 14 boardsto drive the MEMsDM.80 channels/board

16 bit resolutionslow & fast interface(> kHz update)

S. ColleyAO electronic eng.Subaru Telescope

Closed loop WFC

Without prior knowledge,3 frames sufficient forWF measurement

Low Order Wavefront Sensor (LOWFS)

LOWFS performance

Small (<<lambda) wavefront error produces large flux changesin the LOWFS images