Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime
Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime
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分段孔径望远镜与 ZELDA（衍射极限范围内的 Zernike 波前传感器）的精细同相
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发表时间：
2017
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通讯作者：
M. Carbillet
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作者：
P. Janin;M. N’diaye;P. Martinez;A. Vigan;K. Dohlen;M. Carbillet
分段孔径望远镜需要一个从粗对准到监测过程的连续步骤的对准过程，以便为严格的科学操作（如系外行星成像）提供非常高的光学质量图像。最后一步，称为精细定相，要求在衍射限制制度的高灵敏度波前传感和控制系统，以实现纳米精度的片段对齐。在这种情况下，Zernike波前传感器代表了这种校准的有前途的选择。一个被称为Zernike单元的概念，用于分段定相（ZEUS），以前是为地面应用开发的，用于在有限视野图像下运行。然而，这样的概念不适合于与衍射限制图像的精细同相。我们重新访问ZELDA，泽尔尼克传感器，是为测量系外行星直接成像仪中的残余像差而开发的，以测量衍射限制制度中的节段活塞，尖端和倾斜。我们引入了一种新的传感器信号的分析方案，该方案依赖于活塞，尖端和倾斜估计器的每一段，并提供概率的见解来预测作为初始波前误差的函数的闭环校正的成功。该传感器明确且同时地检索分段活塞和倾斜度不对准。我们的计划允许校正这些错误在闭环操作下降到近零残差在几次迭代。该传感器还显示出对其部件的未对准的低灵敏度和对相对明亮的自然引导星星的高操作能力。我们的同相传感器依赖于现有的掩模技术，使该概念在未来的太空任务中已经可用于分段孔径。
Segmented aperture telescopes require an alignment procedure with successive steps from coarse alignment to monitoring process in order to provide very high optical quality images for stringent science operations such as exoplanet imaging. The final step, referred to as fine phasing, calls for a high sensitivity wavefront sensing and control system in a diffraction-limited regime to achieve segment alignment with nanometric accuracy. In this context, Zernike wavefront sensors represent promising options for such a calibration. A concept called the Zernike unit for segment phasing (ZEUS) was previously developed for ground-based applications to operate under seeing-limited images. Such a concept is, however, not suitable for fine cophasing with diffraction-limited images. We revisit ZELDA, a Zernike sensor that was developed for the measurement of residual aberrations in exoplanet direct imagers, to measure segment piston, tip, and tilt in the diffraction-limited regime. We introduce a novel analysis scheme of the sensor signal that relies on piston, tip, and tilt estimators for each segment, and provide probabilistic insights to predict the success of a closed-loop correction as a function of the initial wavefront error. The sensor unambiguously and simultaneously retrieves segment piston and tip-tilt misalignment. Our scheme allows for correction of these errors in closed-loop operation down to nearly zero residuals in a few iterations. This sensor also shows low sensitivity to misalignment of its parts and high ability for operation with a relatively bright natural guide star. Our cophasing sensor relies on existing mask technologies that make the concept already available for segmented apertures in future space missions.