Reininger R, Dufresne E M, Borland M, Beno M A, Young L, Evans P G
Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706, USA.
J Synchrotron Radiat. 2014 Sep;21(Pt 5):1194-9. doi: 10.1107/S1600577514012302. Epub 2014 Jul 31.
Experimental facilities for picosecond X-ray spectroscopy and scattering based on RF deflection of stored electron beams face a series of optical design challenges. Beamlines designed around such a source enable time-resolved diffraction, spectroscopy and imaging studies in chemical, condensed matter and nanoscale materials science using few-picosecond-duration pulses possessing the stability, high repetition rate and spectral range of synchrotron light sources. The RF-deflected chirped electron beam produces a vertical fan of undulator radiation with a correlation between angle and time. The duration of the X-ray pulses delivered to experiments is selected by a vertical aperture. In addition to the radiation at the fundamental photon energy in the central cone, the undulator also emits the same photon energy in concentric rings around the central cone, which can potentially compromise the time resolution of experiments. A detailed analysis of this issue is presented for the proposed SPXSS beamline for the Advanced Photon Source. An optical design that minimizes the effects of off-axis radiation in lengthening the duration of pulses and provides variable X-ray pulse duration between 2.4 and 16 ps is presented.
基于储存电子束射频偏转的皮秒X射线光谱学和散射实验设施面临一系列光学设计挑战。围绕此类光源设计的光束线能够利用具有同步加速器光源稳定性、高重复率和光谱范围的皮秒级短脉冲，在化学、凝聚态物质和纳米尺度材料科学领域开展时间分辨衍射、光谱学和成像研究。经射频偏转的啁啾电子束产生一个垂直扇形的波荡器辐射，其角度与时间之间存在关联。输送到实验中的X射线脉冲持续时间由一个垂直孔径选择。除了中心锥中基波光子能量处的辐射外，波荡器还在中心锥周围的同心环中发射相同的光子能量，这可能会影响实验的时间分辨率。针对先进光子源拟议的SPXSS光束线，对该问题进行了详细分析。本文提出了一种光学设计，可最大限度减少离轴辐射对脉冲持续时间延长的影响，并提供2.4至16皮秒之间可变的X射线脉冲持续时间。
