用强化学习自动校正望远镜像差,提升系外行星成像清晰度。
Focal plane wavefront control with model-based reinforcement learning
- 基于序列相位多样性,用强化学习直接从焦平面上优化相位校正。
- 静态和动态像差下均实现接近最优的光斑抑制与斯特雷尔比。
- 无需系统先验知识,可实时用于大型望远镜的湍流与冠状仪校正。
直接成像潜在宜居系外行星是极大望远镜高对比度成像的主要科学目标。多数此类行星靠近恒星,观测受限于快速变化的大气斑点和准静态非共光路像差(NCPA)。传统NCPA校正依赖机械镜探针,运行中性能受限。本文提出基于机器学习的NCPA控制方法,利用序列相位多样性自动检测并校正动态与静态误差。扩展了自适应光学中强化学习的应用至焦平面控制。提出新型模型基于强化学习算法PO4NCPA,以焦平面图像为输入,通过序列相位多样性确定相位校正,优化无冠状仪与有冠状仪下的点扩散函数,无需系统先验知识。数值模拟显示,该方法在地面望远镜及受水汽扰动影响的红外成像中对静态和动态NCPA均有鲁棒补偿。静态情况下,冠状仪下达到近最优焦面光抑制,无冠状仪时达到近最优斯特雷尔比;动态情况下,性能媲美模态最小二乘重构结合一步延迟积分器。方法适用于极大望远镜口径、矢量涡旋冠状仪,并在光子噪声与背景噪声下仍有效。PO4NCPA为无模型方法,可直接应用于标准成像及任意冠状仪,其亚毫秒推理时间也适合实时低阶大气湍流校正。
原文摘要 · Abstract (English)
The direct imaging of potentially habitable exoplanets is one prime science case for high-contrast imaging instruments on extremely large telescopes. Most such exoplanets orbit close to their host stars, where their observation is limited by fast-moving atmospheric speckles and quasi-static non-common-path aberrations (NCPA). Conventional NCPA correction methods often use mechanical mirror probes, which compromise performance during operation. This work presents machine-learning-based NCPA control methods that automatically detect and correct both dynamic and static NCPA errors by leveraging sequential phase diversity. We extend previous work in reinforcement learning for AO to focal plane control. A new model-based RL algorithm, Policy Optimization for NCPAs (PO4NCPA), interprets the focal-plane image as input data and, through sequential phase diversity, determines phase corrections that optimize both non-coronagraphic and post-coronagraphic PSFs without prior system knowledge. Further, we demonstrate the effectiveness of this approach by numerically simulating static NCPA errors on a ground-based telescope and an infrared imager affected by water-vapor-induced seeing (dynamic NCPAs). Simulations show that PO4NCPA robustly compensates static and dynamic NCPAs. In static cases, it achieves near-optimal focal-plane light suppression with a coronagraph and near-optimal Strehl without one. With dynamics NCPA, it matches the performance of the modal least-squares reconstruction combined with a 1-step delay integrator in these metrics. The method remains effective for the ELT pupil, vector vortex coronagraph, and under photon and background noise. PO4NCPA is model-free and can be directly applied to standard imaging as well as to any coronagraph. Its sub-millisecond inference times and performance also make it suitable for real-time low-order correction of atmospheric turbulence beyond HCI.
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