Bionta M R, Hartmann N, Weaver M, French D, Nicholson D J, Cryan J P, Glownia J M, Baker K, Bostedt C, Chollet M, Ding Y, Fritz D M, Fry A R, Kane D J, Krzywinski J, Lemke H T, Messerschmidt M, Schorb S, Zhu D, White W E, Coffee R N
Université de Toulouse, UPS, Laboratoire Collisions Agrégats Réactivité, IRSAMC, F-31062 Toulouse, France.
The Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
Rev Sci Instrum. 2014 Aug;85(8):083116. doi: 10.1063/1.4893657.
The advent of few femtosecond x-ray light sources brings promise of x-ray/optical pump-probe experiments that can measure chemical and structural changes in the 10-100 fs time regime. Widely distributed timing systems used at x-ray Free-Electron Laser facilities are typically limited to above 50 fs fwhm jitter in active x-ray/optical synchronization. The approach of single-shot timing measurements is used to sort results in the event processing stage. This has seen wide use to accommodate the insufficient precision of active stabilization schemes. In this article, we review the current technique for "measure-and-sort" at the Linac Coherent Light Source at the SLAC National Accelerator Laboratory. The relative arrival time between an x-ray pulse and an optical pulse is measured near the experimental interaction region as a spectrally encoded cross-correlation signal. The cross-correlation provides a time-stamp for filter-and-sort algorithms used for real-time sorting. Sub-10 fs rms resolution is common in this technique, placing timing precision at the same scale as the duration of the shortest achievable x-ray pulses.
少数飞秒X射线光源的出现，为X射线/光泵浦-探测实验带来了希望，这类实验能够测量10 - 100飞秒时间范围内的化学和结构变化。X射线自由电子激光设施中广泛使用的定时系统，在主动X射线/光同步时，其半高宽抖动通常限制在50飞秒以上。单次定时测量方法用于在事件处理阶段对结果进行分类。鉴于主动稳定方案的精度不足，这种方法已得到广泛应用。在本文中，我们回顾了美国SLAC国家加速器实验室直线加速器相干光源处目前的“测量与分类”技术。在实验相互作用区域附近，测量X射线脉冲和光脉冲之间的相对到达时间，作为光谱编码的互相关信号。互相关为用于实时分类的滤波和分类算法提供了时间戳。这种技术的均方根分辨率通常低于10飞秒，使定时精度与可实现的最短X射线脉冲持续时间处于同一量级。
