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High-contrast imaging testbed
K.L. Baker, D.A. Silva, L.A. Poyneer, B.S. Macintosh, B.J. Bauman, D. Palmer, T.P. Remington
and M.A. Delgadillo-Lariz
Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA, USA 94550
ABSTRACT
Several high-contrast imaging systems are currently under construction to enable the detection of extra-solar planets. In
order for these systems to achieve their objectives, however, there is considerable developmental work and testing which
must take place. Given the need to perform these tests, a spatially-filtered Shack-Hartmann adaptive optics system has
been assembled to evaluate new algorithms and hardware configurations which will be implemented in these future
high-contrast imaging systems. In this article, construction and phase measurements of a membrane "woofer" mirror are
presented. In addition, results from closed-loop operation of the assembled testbed with static phase plates are presented.
The testbed is currently being upgraded to enable operation at speeds approaching 500 hz and to enable studies of the
interactions between the woofer and tweeter deformable mirrors.
Keywords: Adaptive optics, high contrast, Shack-Hartmann wave-front sensor, spatial filter
1. INTRODUCTION
Future adaptive optics systems on ground-based telescopes will enable direct observation of extra-solar Jovian planets.
The observation of the reflected or emitted spectra from these planets at high spectral resolution will provide valuable
scientific information regarding their atmospheric constituents which is unattainable with current techniques used to
study these planets such as the Doppler-shift of or intensity variation in the parent stars emission. Likewise, these
instruments will study such planet populations at distances which are farther away from the parent star than current
techniques have thus-far achieved and as such are complimentary to the techniques mentioned above. There are several
attractive options for spatially-filtered wave-front sensors on these adaptive optics systems including pyramid sensors in
direct phase model, interferometers2 and Shack-Hartmann wave-front sensors3. The first generation of these instruments,
such as the Gemini Planet Imager(GPI), will employ a spatially-filtered Shack-Hartmann wave-front sensor.4 In order for
this instrument, as well as future instruments, to be successful, a number of algorithms and hardware configurations must
be tested in a laboratory setting before the implementation of these instruments on telescopes can take place.
In this article we report on the development of a spatially-filtered Shack-Hartmann wave-front sensor which will be used
to test the algorithms and hardware configurations that will be implemented on the Gemini Planet Imager. The testbed,
along with its components, is described in detail in section 2. The results from running the testbed in closed-loop mode
with static phase plates is presented in section 3 and the results are summarized in section 4 of this article.
2. EXPERIMENTAL LAYOUT
The optical layout of the high-contrast laboratory breadboard system is shown below in Figure 1. The testbed consists
primarily of a spatially-filtered Shack-Hartmann wavefront sensor, a MEMS-based spatial-light-modulator functioning
as a "tweeter" built by the Boston Micromachines Corporation (BMC), a membrane mirror functioning as a "woofer", a
1 mrad tip-tilt stage manufactured by Piezosystems Jena, a light source, a wave-front aberrator, a far-field camera and
computer hardware/software to analyze the wave-front and implement the phase correction. The system is at present
controlled using the IDL programming language which is currently running the system at about 1 hz. Because of this
relatively slow speed, the results presented below represent a correction of the 1024 actuator MEMS device with
stationary phase plates. The membrane mirror and tip-tilt stage have been tested separately in an interferometer but have
not yet been integrated into the adaptive optics testbed. A description of the membrane mirror is given in greater detail in
section 2.1 below. As currently configured, the testbed can be run with either a single mode fiber-coupled HeNe laser at
632 nm or a superluminescent diode at 680 nm with a bandwidth of 8 nm for its light source. For the results presented
below, a HeNe laser was utilized as the light source.
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Baker, K. L.; Silva, D. A.; Poyneer, L. A.; Macintosh, B. S.; Bauman, B. J.; Palmer, D. et al. High-contrast imaging testbed, article, January 23, 2008; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc896643/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.