HIGH-DYNAMIC-RANGE IMAGING USING A DEFORMABLE MIRROR FOR SPACE CORONOGRAPHY

The need for high-dynamic-range imaging is crucial in many astronomical fields, such as extra-solar planet direct detection, extragalactic science, and circumstellar imaging. Using a high-quality coronograph, dynamic ranges of up to 10(5) have been achieved. However the ultimate limitations of coronographs do not come from their optical performances, but from scattering due to imperfections in the optical surfaces of the collecting system. We propose the use of a deformable mirror to correct these imperfections and decrease the scattering level in local regions called ''dark holes.'' Using this technique will enable imaging of fields with dynamic ranges exceeding 10(8). We show that the dark-hole algorithm results in a lower scattering level than simply minimizing the rms figure error (maximum-strehl-ratio algorithm). The achievable scattering level inside the dark-hole region will depend on the number of mirror actuators, the surface quality of the telescope, the single-actuator influence function, and the observing wavelength. We have simulated cases with a 37X37 deformable mirror using data from the Hubble Space Telescope optics without spherical aberrations and have demonstrated dark holes with rectangular and annular shapes. We also present a preliminary concept of a monolithic, fully integrated, high-density deformable mirror which can be used for this type of space application.