19 September 2007 Amplitude variations on the ExAO testbed
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High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require excellent wavefront control and diffraction suppression. At the Laboratory for Adaptive Optics on the Extreme Adaptive Optics testbed, we have already demonstrated wavefront control of better than 1 nm rms within controllable spatial frequencies. Corresponding contrast measurements, however, are limited by amplitude variations, including those introduced by the micro-electrical-mechanical-systems (MEMS) deformable mirror. Results from experimental measurements and wave optic simulations of amplitude variations on the ExAO testbed are presented. We find systematic intensity variations of about 2% rms, and intensity variations with the MEMS to be 6%. Some errors are introduced by phase and amplitude mixing because the MEMS is not conjugate to the pupil, but independent measurements of MEMS reflectivity suggest that some error is introduced by small non-uniformities in the reflectivity.
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Julia W. Evans, Julia W. Evans, Sandrine Thomas, Sandrine Thomas, Daren Dillon, Daren Dillon, Donald Gavel, Donald Gavel, Donald Phillion, Donald Phillion, Bruce Macintosh, Bruce Macintosh, } "Amplitude variations on the ExAO testbed", Proc. SPIE 6693, Techniques and Instrumentation for Detection of Exoplanets III, 669312 (19 September 2007); doi: 10.1117/12.735741; https://doi.org/10.1117/12.735741

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