Improved Approach to Exoplanet Coronagraphy

Visible nulling coronagraphy and interferometry requires that the wavefront errors be held to unprecedented precision in the presence of environmental disturbances. A Null Diversity algorithm is used to first attain the precision, but it does not execute at high enough temporal bandwidth to hold the precision for long periods of time (hours). The environmental changes, mostly vibration and jitter with some thermal drift, can be rapidly varying and thus require a fast control algorithm. To perform rapid control, an algorithm, based upon a series of approximations, has been developed and simulated at NASA Goddard Space Flight Center for the sensing and control, in closed loop, of extremely precise wave-front errors in an interferometer. It operates over the range of ~5 nanometers rms down to <100 picometers rms in closed loop at high bandwidth (~20 Hz) and is used to hold (i.e. maintain) the requisite wavefront error.