用非平衡调零干涉仪对系外行星成像日冕仪进行精确的波前校正
Precise Wavefront Correction with an Unbalanced Nulling Interferometer for Exo-Planet Imaging Coronagraphs
摘要：
以小角距（几个λ/D单位）直接探测系外行星（10^9 - 10^10对比度）为目标的极高动态范围日冕仪通常要求输入波前质量为波长RMS的万分之一。我们提出了一种新的方法的基础上的预光学设置，其行为部分作为一个低效率的电晕放电，部分作为一个高灵敏度的波前像差补偿器（相位和振幅）。这两种效应的组合导致高度精确的校正波前。首先，（强度）不平衡调零干涉仪（UNI）执行波前电场的一部分的抑制。然后，重新组合的输出波前使其输入像差放大。由于不平衡的复合方案，像差可以没有相位奇点（零），并且因此可以通过下游相位和幅度校正（PAC）自适应光学系统使用两个可变形反射镜来补偿。在像平面中，UNI-PAC组合降低了中心恒星的峰值强度和斑点晕的噪声水平：输出校正的波前像差可以解释为对初始（最终已经校正）入射波前像差的改进补偿。重要的结论是，使用UNI-PAC的光学设置中并非所有元件都需要达到λ/10000 rms表面误差质量。
英文摘要：
Very high dynamical range coronagraphs targeting direct exo-planet detection (10^9 - 10^10 contrast) at small angular separation (few lambda/D units) usually require an input wavefront quality on the order of ten thousandths of wavelength RMS. We propose a novel method based on a pre-optics setup that behaves partly as a low-efficiency coronagraph, and partly as a high-sensitivity wavefront aberration compensator (phase and amplitude). The combination of the two effects results in a highly accurate corrected wavefront. First, an (intensity-) unbalanced nulling interferometer (UNI) performs a rejection of part of the wavefront electric field. Then the recombined output wavefront has its input aberrations magnified. Because of the unbalanced recombination scheme, aberrations can be free of phase singular points (zeros) and can therefore be compensated by a downstream phase and amplitude correction (PAC) adaptive optics system, using two deformable mirrors. In the image plane, the central star's peak intensity and the noise level of its speckled halo are reduced by the UNI-PAC combination: the output-corrected wavefront aberrations can be interpreted as an improved compensation of the initial (eventually already corrected) incident wavefront aberrations. The important conclusion is that not all the elements in the optical setup using UNI-PAC need to reach the lambda/10000 rms surface error quality.
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