Cool Stars 14 - Submitted Abstract # 337
This version created on 05 October 2006

Wavefront Control in a Shaped-Pupil Coronagraph:  First Results from
the Princeton Testbed


Ruslan  Belikov
Amir  Give'on
Laurent  Pueyo
Eric  Cady
Jason  Kay
Michael  Carr
N. Jeremy  Kasdin

Direct imaging of extrasolar planets, and terrestrial planets in
particular, is an exciting but difficult problem requiring a telescope
imaging system with unprecedented levels of contrast.  One promising
design is the Shaped Pupil Coronagraph (SPC), pioneered by our lab
over the past several years.  The SPC was designed to achieve 10^10
contrast at an inner working angle of 4 lambda/D, based on the
requirements of NASA's space-based Terrestrial Planet Finder
Coronagraph (TPF-C) mission.  However, it has long been recognized
that a key problem in achieving these requirements in practice is
estimation and control of wavefront aberrations in the optics of the
telescope, and doing so over a broad spectral band.  In earlier work,
we have described the manufacture and test of the SPC on our testbed
at Princeton, reaching of 10^5 contrast at 4 lambda/D in air without
any wavefront control, as well as reaching almost 10^8 contrast in
vacuum with wavefront control on JPL's testbed.  In this work, we show
the first results of performing wavefront control on our testbed.  We
have utilized a 32x32 deformable mirror manufactured by the Boston
Micromachines Corporation.  The corrections were tested at several
wavelengths and in white light, improving contrast by more than a
factor of 10.  We discuss the contrast limiting factors and propose
ways of beating them.  The main limiting factor currently is the
resolution of the electronics, and we project that 10^7 or 10^8
contrast is possible at 4 lambda/D before our air environment is the
main limit.  

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