用LBTI的PHASECam实现n个$λ$相位误差校正的双波段方法
A two-band approach to n$λ$ phase error corrections with LBTI's PHASECam
摘要：
PHASECam是大型双目望远镜干涉仪（LBTI）的相位传感器，一种近红外相机，用于测量大型双目望远镜（LBT）两个AO校正孔径之间的倾斜/倾斜和相位变化。当前在1 kHz的H（1.65 $μ$ m）和K（2.2 $μ$ m）波段中执行倾斜/倾斜和相位感测，并且K波段相位遥测用于向系统发送倾斜/倾斜和光程差（OPD）校正。然而，在范围[- $π$，$π$ ]之外的相位变化未被感测到，并且因此在闭环操作期间未被完全校正。PHASECam的相位展开算法试图缓解这个问题，但在快速、大相位变化的情况下偶尔仍会失败。这可能会导致条纹跳跃，在这种情况下，展开的相位将不正确的波长或更多。这目前可以由观察者手动校正，但这是低效的。需要一种更可靠和自动化的解决方案，特别是当LBTI开始委托需要鲁棒的主动相位控制的其他模式时，包括受控多轴（Fizeau）干涉测量和双孔径非冗余孔径掩模干涉测量。我们提出了一种多波长的条纹跳跃捕获和校正的方法，其中包括K波段和目前未使用的H波段相位遥测之间的直接比较。
英文摘要：
PHASECam is the Large Binocular Telescope Interferometer's (LBTI) phase sensor, a near-infrared camera which is used to measure tip/tilt and phase variations between the two AO-corrected apertures of the Large Binocular Telescope (LBT). Tip/tilt and phase sensing are currently performed in the H (1.65 $μ$m) and K (2.2 $μ$m) bands at 1 kHz, and the K band phase telemetry is used to send tip/tilt and Optical Path Difference (OPD) corrections to the system. However, phase variations outside the range [-$π$, $π$] are not sensed, and thus are not fully corrected during closed-loop operation. PHASECam's phase unwrapping algorithm, which attempts to mitigate this issue, still occasionally fails in the case of fast, large phase variations. This can cause a fringe jump, in which case the unwrapped phase will be incorrect by a wavelength or more. This can currently be manually corrected by the observer, but this is inefficient. A more reliable and automated solution is desired, especially as the LBTI begins to commission further modes which require robust, active phase control, including controlled multi-axial (Fizeau) interferometry and dual-aperture non-redundant aperture masking interferometry. We present a multi-wavelength method of fringe jump capture and correction which involves direct comparison between the K band and currently unused H band phase telemetry.
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