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

The need for high-dynamic-range imaging is crucial in many astronomica l fields, such as extra-solar planet direct detection, extragalactic s cience, and circumstellar imaging. Using a high-quality coronograph, d ynamic ranges of up to 10(5) have been achieved. However the ultimate limitations of coronographs do not come from their optical performance s, but from scattering due to imperfections in the optical surfaces of the collecting system. We propose the use of a deformable mirror to c orrect these imperfections and decrease the scattering level in local regions called ''dark holes.'' Using this technique will enable imagin g of fields with dynamic ranges exceeding 10(8). We show that the dark -hole algorithm results in a lower scattering level than simply minimi zing the rms figure error (maximum-strehl-ratio algorithm). The achiev able scattering level inside the dark-hole region will depend on the n umber of mirror actuators, the surface quality of the telescope, the s ingle-actuator influence function, and the observing wavelength. We ha ve simulated cases with a 37X37 deformable mirror using data from the Hubble Space Telescope optics without spherical aberrations and have d emonstrated dark holes with rectangular and annular shapes. We also pr esent a preliminary concept of a monolithic, fully integrated, high-de nsity deformable mirror which can be used for this type of space appli cation.