The Follow-up X-ray Telescope (FXT), a key payload onboard the Einstein Probe sallite (EP), is equipped with a Wolter-I x-ray focusing mirror system. We introduce the principle of such a mirror system and analyze the influence of the mirror gap in the multishell nested mirror of the FXT on the effective area, stray-light ratio, and vignetting. To ensure that no occlusion occurs within adjacent shells and minimize stray-light ratio, the size of the gap is set to a optimized value for corresponding shell. We finished a design of a 54-shell mirror system according to these results. The optical performance of the design was then simulated using a Monte Carlo algorithm and the ray-tracing principle. The simulation shows that the effective area is 414.5 ± 0.2 cm2 at 1.25 keV (considering the spider), and the field of view is 64 arcmin in diameter. These parameters meet the optical requirements of the FXT.

中文翻译：

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爱因斯坦探针卫星后续X射线望远镜的光学设计和仿真

后续X射线望远镜（FXT）是爱因斯坦探测沙岩（EP）的主要有效载荷，配备了Wolter-I X射线聚焦镜系统。我们介绍了这种反光镜系统的原理，并分析了FXT多壳嵌套反光镜中反光镜间隙对有效面积，杂散光比和渐晕的影响。为了确保在相邻的壳体内不会发生遮挡，并使杂散光比最小，将间隙的大小设置为对应壳体的最佳值。根据这些结果，我们完成了54壳镜系统的设计。然后，使用蒙特卡洛算法和光线追踪原理对设计的光学性能进行仿真。仿真显示，在1.25 keV时，有效面积为414.5±0.2 cm2（考虑星形轮），并且视场的直径为64 arcmin。