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Stellar coronagraphs rely on deformable mirrors (DMs) to correct wavefronterrors and create high contrast images. Imperfect control of the DM limits theachievable contrast and, therefore, the DM control electronics must providefine surface height resolution and low noise. Here, we study the impact ofquantization errors due to the DM electronics on the image contrast usingexperimental data from the High Contrast Imaging Testbed (HCIT) facility atNASA's Jet Propulsion Laboratory (JPL). We find that the simplest analyticalmodel gives optimistic predictions compared to real cases, with contrast up to3 times better, which leads to DM surface height resolution requirements thatare incorrectly relaxed by 70%. We show that taking into account the DMactuator shape, or influence function, improves the analytical predictions.However, we also find that end-to-end numerical simulations of the wavefrontsensing and control process provide the most accurate predictions and recommendsuch an approach for setting robust requirements on the DM control electronics.From our experimental and numerical results, we conclude that a surface heightresolution of approximately 6pm is required for imaging temperate terrestrialexoplanets around Solar-type stars at wavelengths as small as 450nm withcoronagraph instruments on future space telescopes. Finally, we list therecognizable characteristics of quantization errors that may help determine ifthey are a limiting factor.

journal of astronomical telescopes, instruments, and systems

Microelectromechanical deformable mirror development for high-contrast  imaging, part 2: the impact of quantization errors on coronagraph image  contrast