Yu Jun, Shen Zhengxiang, Sheng Pengfeng, Wang Xiaoqiang, Hailey Charles J, Wang Zhanshan
Appl Opt. 2018 Mar 1;57(7):B74-B82. doi: 10.1364/AO.57.000B74.
The nested grazing incidence telescope can achieve a large collecting area in x-ray astronomy, with a large number of closely packed, thin conical mirrors. Exploiting the surface metrological data, the ray tracing method used to reconstruct the shell surface topography and evaluate the imaging performance is a powerful tool to assist iterative improvement in the fabrication process. However, current two-dimensional (2D) ray tracing codes, especially when utilized with densely sampled surface shape data, may not provide sufficient accuracy of reconstruction and are computationally cumbersome. In particular, 2D ray tracing currently employed considers coplanar rays and thus simulates only these rays along the meridional plane. This captures axial figure errors but leaves other important errors, such as roundness errors, unaccounted for. We introduce a semianalytic, three-dimensional (3D) ray tracing approach for x-ray optics that overcomes these shortcomings. And the present method is both computationally fast and accurate. We first introduce the principles and the computational details of this 3D ray tracing method. Then the computer simulations of this approach compared to 2D ray tracing are demonstrated, using an ideal conic Wolter-I telescope for benchmarking. Finally, the present 3D ray tracing is used to evaluate the performance of a prototype x-ray telescope fabricated for the enhanced x-ray timing and polarization mission.
嵌套掠入射望远镜在X射线天文学中可以通过大量紧密排列的薄圆锥镜实现较大的收集面积。利用表面计量数据，用于重建镜面表面形貌和评估成像性能的光线追迹方法是协助制造过程迭代改进的有力工具。然而，当前的二维（2D）光线追迹代码，特别是在与密集采样的表面形状数据一起使用时，可能无法提供足够的重建精度，并且计算量很大。特别是，目前采用的二维光线追迹考虑共面光线，因此仅模拟沿子午面的这些光线。这捕获了轴向形状误差，但忽略了其他重要误差，如圆度误差。我们引入了一种用于X射线光学的半解析三维（3D）光线追迹方法，该方法克服了这些缺点。并且本方法在计算上既快速又准确。我们首先介绍这种3D光线追迹方法的原理和计算细节。然后，使用理想的圆锥沃尔特-Ⅰ型望远镜作为基准，展示了该方法与2D光线追迹相比的计算机模拟。最后，使用当前的3D光线追迹来评估为增强X射线计时和偏振任务制造的原型X射线望远镜的性能。
