论文标题
衍射有限X射线望远镜的光学设计
Optical design of diffraction-limited X-ray telescopes
论文作者
论文摘要
具有微弧形（$μ$ a）角度分辨率的天文成像可以实现突破性的科学发现。 X射线成像仪设计的先前所述的$μ$已成为有限有效收集区域的干涉仪。在这里，我们描述了X射线望远镜在具有较大有效区域的宽能带上实现衍射有限的性能，采用带有放牧镜的嵌套壳结构，同时匹配所有壳之间的光路长度。我们提出了两种紧凑型嵌套壳陶器2型放牧望远镜设计，用于衍射限制的X射线成像：一种微型Arcsecond望远镜设计，具有14 $μ$作为角度分辨率，2.9 m $^2 $^2 $^2 $的有效面积为5 kev photon Energy（$λ$ = 0.25 nm）和小米尔克（$λ$ = 0.25 nm），零售店和小米尔卡（$λ$ = 0.25 nm）， $μ$作为分辨率和645 cm $^2 $有效区域为1 keV（$λ$ = 1.24 nm）。我们描述了如何匹配紧凑型镜组件中所有壳之间的光路长度，并研究色差和轴畸变。色差是由于镜面的总外部反射而导致的，我们通过稍微调整每个镜面壳的路径长度来大大减轻其效果。镜面高度误差和衍射有限性能的对齐要求具有挑战性，但在未来几十年中可以说是可以实现的。由于衍射有限的X射线望远镜的焦距非常大（$ f/d $ 〜10 $^5 $），因此唯一重要的离轴异常是场的曲率，因此，对于平面检测器而言，1弧形视野是可行的。检测器必须与镜组件形成，但相对定位公差在1 m的距离内，距离数十万到数百公里。尽管实现衍射有限的X射线成像面临许多挑战，但我们没有找到任何基本障碍。
Astronomical imaging with micro-arcsecond ($μ$as) angular resolution could enable breakthrough scientific discoveries. Previously-proposed $μ$as X-ray imager designs have been interferometers with limited effective collecting area. Here we describe X-ray telescopes achieving diffraction-limited performance over a wide energy band with large effective area, employing a nested-shell architecture with grazing-incidence mirrors, while matching the optical path lengths between all shells. We present two compact nested-shell Wolter Type 2 grazing-incidence telescope designs for diffraction-limited X-ray imaging: a micro-arcsecond telescope design with 14 $μ$as angular resolution and 2.9 m$^2$ of effective area at 5 keV photon energy ($λ$=0.25 nm), and a smaller milli-arcsecond telescope design with 525 $μ$as resolution and 645 cm$^2$ effective area at 1 keV ($λ$=1.24 nm). We describe how to match the optical path lengths between all shells in a compact mirror assembly, and investigate chromatic and off-axis aberrations. Chromatic aberration results from total external reflection off of mirror surfaces, and we greatly mitigate its effects by slightly adjusting the path lengths in each mirror shell. The mirror surface height error and alignment requirements for diffraction-limited performance are challenging but arguably achieveable in the coming decades. Since the focal ratio for a diffraction-limited X-ray telescope is extremely large ($f/D$~10$^5$), the only important off-axis aberration is curvature of field, so a 1 arcsecond field of view is feasible with a flat detector. The detector must fly in formation with the mirror assembly, but relative positioning tolerances are on the order of 1 m over a distance of some tens to hundreds of kilometers. While there are many challenges to achieving diffraction-limited X-ray imaging, we did not find any fundamental barriers.
