In the last decade, more than 1000 candidate exoplanets have been discovered. About 5% of Sun-like stars host an Earth-size exoplanet with an orbital period of 200???400 days, which could support liquid water & life. By observing spectral signatures of these planets’ atmospheres over a range of visible wavelengths, it is possible determine the gases they contain. However, it is difficult to measure light reflecting off a dim planet positioned next to a bright star. The contrast level required to image an Earth-like planet around a Sun-like star is about 10???10. High-performance coronagraphs can be used to block light from a star & allow observation of an orbiting planet. Any speckles in the background of the image, however, may still be brighter than the planet. Speckles in astronomical images are the result of wavefront corruption caused by effects such as atmospheric turbulence (a primary concern w ground-based telescopes), optical imperfections, thermal distortions, & diffraction. Aberrations in the pupil plane of a telescope can lead to degradation of the point spread function & speckles in the image plane. The higher the spatial frequency of pupil-plane aberrations, the further off-axis the corresponding speckle will be in the image plane. The speckle may then be located at the expected position of a planet. Deformable mirrors (DMs) have high actuator counts & densities.
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