Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland.
J Synchrotron Radiat. 2011 Mar;18(Pt 2):134-42. doi: 10.1107/S0909049510054452. Epub 2011 Jan 29.
Operation of an X-ray spectrometer based on a spherical variable-line-spacing (VLS) grating is analyzed using dedicated ray-tracing software allowing fast optimization of the grating parameters and spectrometer geometry. The analysis is illustrated with optical design of a model spectrometer to deliver a resolving power above 20400 at a photon energy of 930 eV (Cu L-edge). With this energy taken as reference, the VLS coefficients are optimized to cancel the lineshape asymmetry (mostly from the coma aberrations) as well as minimize the symmetric aberration broadening at large grating illuminations, dramatically increasing the aberration-limited vertical acceptance of the spectrometer. For any energy away from the reference, corrections to the entrance arm and light incidence angle on the grating are evaluated to maintain the exactly symmetric lineshape. Furthermore, operational modes when these corrections are coordinated are evaluated to maintain either energy-independent focal curve inclination or maximal aberration-limited spectrometer acceptance. The results are supported by analytical evaluation of the coma term of the optical path function. This analysis thus gives a recipe for designing a high-resolution spherical VLS grating spectrometer operating with negligible aberrations at large acceptance and over an extended energy range.
基于球形变线距（VLS）光栅的 X 射线光谱仪的操作，使用专用的光线追踪软件进行分析，该软件允许快速优化光栅参数和光谱仪几何形状。通过对模型光谱仪的光学设计进行分析，说明了这种方法，该光谱仪在光子能量为 930 eV（Cu L 边缘）时的分辨率超过 20400。以这个能量为参考，优化了 VLS 系数，以消除线形状不对称（主要来自彗差像差），并最小化大光栅照明下的对称像差展宽，极大地提高了光谱仪的像差限制的垂直接收度。对于任何偏离参考能量的情况，评估了进入臂和光栅上光入射角的校正，以保持完全对称的线形状。此外，评估了这些校正协调的操作模式，以保持能量独立的焦曲线倾斜或最大的像差限制的光谱仪接收度。该分析通过对光路函数的彗差项进行分析评估得到了结果。因此，该分析给出了一种设计高分辨率球形 VLS 光栅光谱仪的方法，该光谱仪在大接收度和扩展的能量范围内具有可忽略的像差。
