Predictive wavefront control on Keck II adaptive optics bench: on-sky coronagraphic results
Predictive wavefront control on Keck II adaptive optics bench: on-sky coronagraphic results
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Keck II 自适应光学平台上的预测波前控制：空中日冕结果
DOI：
10.1117/1.jatis.8.2.029006
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
P. Wizinowich
中科院分区：
文献类型：
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作者：
M. V. van Kooten;R. Jensen;Sylvain Cetre;S. Ragland;C. Bond;J. Fowler;P. Wizinowich
抽象的。用于地面高对比度成像的自适应光学（AO）系统的行为决定了仪器可实现的对比度。在大气的相干时间与AO系统的速度相比较短的条件下，伺服滞后误差可以成为AO系统的主要误差项。虽然AO系统测量波前误差并随后应用校正（通常总共花费一毫秒或几毫秒），但望远镜上方的大气湍流已经改变，导致伺服滞后误差。除了降低斯特列尔比之外，伺服滞后误差还导致斑点沿着日冕图像中的主导风矢量的方向积累，严重限制了小角度间隔处的对比度。缓解该问题的一种策略是预测湍流在延迟时间上的演变。我们的预测波前控制算法最大限度地减少，在均方意义上，波前误差的延迟，并已实施的凯克II AO工作台。我们报告我们的算法的最新结果，并讨论算法本身的更新。我们探讨如何调整各种过滤器参数的基础上白天的实验室测试和天空测试。我们发现减少剩余均方波前误差的预测相比，泄漏积分器（凯克的标准控制器）上实现凯克三个单独的夜晚。最后，我们首次提出了白天和天空测试的对比度改进。使用凯克的NIRC 2仪器的L波段涡旋日冕仪，我们发现在3 λ / D的分离处对比度增益高达2，在更大的分离处（3 − 7 λ / D）高达3。
Abstract. The behavior of an adaptive optics (AO) system for ground-based high contrast imaging dictates the achievable contrast of the instrument. In conditions where the coherence time of the atmosphere is short compared with the speed of the AO system, the servo-lag error can become the dominant error term of the AO system. While the AO system measures the wavefront error and subsequently applies a correction (typically taking a total of one or a few milliseconds), the atmospheric turbulence above the telescope has changed resulting in the servo-lag error. In addition to reducing the Strehl ratio, the servo-lag error causes a build-up of speckles along the direction of the dominant wind vector in the coronagraphic image, severely limiting the contrast at small angular separations. One strategy to mitigate this problem is to predict the evolution of the turbulence over the delay time. Our predictive wavefront control algorithm minimizes, in a mean square sense, the wavefront error over the delay and has been implemented on the Keck II AO bench. We report on the latest results of our algorithm and discuss updates to the algorithm itself. We explore how to tune various filter parameters based on both daytime laboratory tests and on-sky tests. We show a reduction in residual-mean-square wavefront error for the predictor compared with the leaky integrator (the standard controller for Keck) implemented on Keck for three separate nights. Finally, we present contrast improvements for daytime and on-sky tests for the first time. Using the L-band vortex coronagraph for Keck’s NIRC2 instrument, we find a contrast gain of up to 2 at a separation of 3 λ / D and up to 3 for larger separations (3 − 7 λ / D).