We investigate the focal plane wavefront sensing technique, known as Phase Diversity, at the scientific focal plane of a segmented mirror telescope with an adaptive optics (AO) system. We specifically consider an optical system imaging a point source in the context of (i) an artificial source within the telescope structure and (ii) from AO-corrected images of a bright star. From our simulations, we reliably disentangle segmented telescope phasing errors from non-common path aberrations (NCPA) for both a theoretical source and on-sky, AO-corrected images where we have simulated the Keck/NIRC2 system. This quantification from on-sky images is appealing, as it is sensitive to the cumulative wavefront perturbations of the entire optical train; disentanglement of phasing errors and NCPA is therefore critical, where any potential correction to the primary mirror from an estimate must contain minimal NCPA contributions. Our estimates require a 1-min sequence of short-exposure, AO-corrected images; by exploiting a slight modification to the AO-loop, we find that 75 defocused images produce reliable estimates. We demonstrate a correction from our estimates to the primary and deformable mirror results in a wavefront error reduction of up to 67 per cent and 65 per cent for phasing errors and NCPA, respectively. If the segment phasing errors on the Keck primary are of the order of ∼130 nm RMS, we show we can improve the H-band Strehl ratio by up to 10 per cent by using our algorithm. We conclude our technique works well to estimate NCPA alone from on-sky images, suggesting it is a promising method for any AO-system.

中文翻译：

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从自适应光学校正图像同时估计分段望远镜相位误差和非常见路径像差

我们在具有自适应光学 (AO) 系统的分段镜面望远镜的科学焦平面上研究焦平面波前传感技术，称为相位分集。我们特别考虑了在以下情况下对点源成像的光学系统：（i）望远镜结构内的人造源和（ii）来自明亮恒星的 AO 校正图像。从我们的模拟中，我们可靠地将分段望远镜相位误差与非公共路径像差 (NCPA) 分离，用于理论源和天空中的 AO 校正图像，其中我们模拟了 Keck/NIRC2 系统。这种来自天空图像的量化很有吸引力，因为它对整个光学系统的累积波前扰动很敏感。因此，消除相位误差和 NCPA 至关重要，从估计中对主镜的任何潜在修正必须包含最小的 NCPA 贡献。我们的估计需要 1 分钟的短曝光、AO 校正图像序列；通过对 AO 循环进行轻微修改，我们发现 75 个散焦图像产生了可靠的估计。我们证明了我们对主镜和可变形镜的估计的校正导致相位误差和 NCPA 的波前误差分别减少高达 67% 和 65%。如果 Keck 初级上的分段相位误差约为 130 nm RMS，我们表明我们可以通过使用我们的算法将 H 波段 Strehl 比率提高多达 10%。我们得出结论，我们的技术可以很好地从天空图像中单独估计 NCPA，这表明它对于任何 AO 系统都是一种很有前途的方法。