European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany.
J Synchrotron Radiat. 2022 Sep 1;29(Pt 5):1299-1308. doi: 10.1107/S1600577522007627. Epub 2022 Aug 23.
The SASE3 soft X-ray beamline at the European XFEL has been designed and built to provide experiments with a pink or monochromatic beam in the photon energy range 250-3000 eV. Here, the focus is monochromatic operation of the SASE3 beamline, and the design and performance of the SASE3 grating monochromator are reported. The unique capability of a free-electron laser source to produce short femtosecond pulses of a high degree of coherence challenges the monochromator design by demanding control of both photon energy and temporal resolution. The aim to transport close to transform-limited pulses poses very high demands on the optics quality, in particular on the grating. The current realization of the SASE3 monochromator is discussed in comparison with optimal design performance. At present, the monochromator operates with two gratings: the low-resolution grating is optimized for time-resolved experiments and allows for moderate resolving power of about 2000-5000 along with pulse stretching of a few to a few tens of femtoseconds RMS, and the high-resolution grating reaches a resolving power of 10 000 at the cost of larger pulse stretching.
SASE3 软 X 射线光束线在欧洲 XFEL 设计和建造，以提供实验用的光子能量范围 250-3000 电子伏特的粉红色或单色光束。这里，重点是 SASE3 光束线的单色操作，并报告了 SASE3 光栅单色仪的设计和性能。自由电子激光源产生短飞秒脉冲的高度相干性的独特能力，通过对光子能量和时间分辨率的控制，对单色仪设计提出了挑战。接近变换极限脉冲的传输对光学质量，特别是对光栅提出了非常高的要求。目前，与最佳设计性能相比，讨论了 SASE3 单色仪的实现。目前，单色仪有两个光栅：低分辨率光栅是为时间分辨实验优化的，并允许大约 2000-5000 的中等分辨率和几到几十飞秒 RMS 的脉冲拉伸，而高分辨率光栅以更大的脉冲拉伸为代价达到 10000 的分辨率。
