Stellar coronagraphs rely on deformable mirrors (DMs) to correct wavefront errors and create high-contrast images. Imperfect control of the DM limits the achievable contrast, and therefore, the DM control electronics must provide fine surface height resolution and low noise. We study the impact of quantization errors due to the DM electronics on the image contrast using experimental data from the High Contrast Imaging Testbed facility at NASA’s Jet Propulsion Laboratory. We find that the simplest analytical model gives optimistic predictions compared to real cases, with contrast up to 3 times better, which leads to DM surface height resolution requirements that are incorrectly relaxed by 70%. We show that taking into account the DM actuator shape, or influence function, improves the analytical predictions. However, we also find that end-to-end numerical simulations of the wavefront sensing and control process provide the most accurate predictions and recommend such an approach for setting robust requirements on the DM control electronics. From our experimental and numerical results, we conclude that a surface height resolution of ∼6 pm is required for imaging temperate terrestrial exoplanets around solar-type stars at wavelengths as small as 450 nm with coronagraph instruments on future space telescopes. Finally, we list the recognizable characteristics of quantization errors that may help determine if they are a limiting factor.

中文翻译：

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用于高对比度成像的微机电可变形反射镜开发，第2部分：量化误差对日冕仪图像对比度的影响

恒星日冕仪依靠可变形镜（DM）校正波前误差并创建高对比度图像。DM的控制不完善限制了可达到的对比度，因此DM控制电子设备必须提供良好的表面高度分辨率和低噪音。我们使用来自NASA喷气推进实验室的高对比度成像测试台设施的实验数据，研究了由于DM电子设备导致的量化误差对图像对比度的影响。我们发现，与实际情况相比，最简单的分析模型可以提供乐观的预测，对比度要高出3倍，从而导致DM表面高度分辨率要求被错误地放松了70％。我们表明，考虑到DM执行器的形状或影响函数，可以改善分析预测。然而，我们还发现，波前传感和控制过程的端到端数值模拟提供了最准确的预测，并推荐了这种方法来设置对DM控制电子设备的严格要求。根据我们的实验和数值结果，我们得出结论，在未来的太空望远镜上用日冕仪对波长为450 nm的太阳型恒星周围的温带地球外行星进行成像时，需要约6 pm的表面高度分辨率。最后，我们列出了量化误差的可识别特征，这些特征可能有助于确定量化误差是否是限制因素。根据我们的实验和数值结果，我们得出结论，在未来的太空望远镜上用日冕仪对波长为450 nm的太阳型恒星周围的温带地球外行星进行成像时，需要约6 pm的表面高度分辨率。最后，我们列出了量化误差的可识别特征，这些特征可能有助于确定量化误差是否是限制因素。根据我们的实验和数值结果，我们得出结论，在未来的太空望远镜上用日冕仪对波长为450 nm的太阳型恒星周围的温带地球外行星进行成像时，需要约6 pm的表面高度分辨率。最后，我们列出了量化误差的可识别特征，这些特征可能有助于确定量化误差是否是限制因素。