To fully optimize the operation of a high-gain free-electron laser (FEL) facility and to offer opportunities for time-resolved experiments, a highly accurate synchronization between an electron bunch and a seeded laser is required. Thus, a high-precision and high-resolution beam arrival and flight time measurement system is built at the Shanghai soft X-ray FEL (SXFEL) facility. For the SXFEL, a beam arrival time resolution better than 100 fs is required. A phase cavity-based detection scheme for this measurement has already been adopted at the SXFEL. To further optimize system performance, the impacts of clock jitter, trigger jitter, and signal analysis length on the measurement uncertainties are analyzed, and related subsystems are upgraded and optimized accordingly. The beam arrival time is successfully measured, and the initial measurement uncertainty is better than 45 fs. Furthermore, a dual-cavity mixing scheme is realized to measure the beam flight time or pseudo-beam arrival time, and the measurement resolution of the beam flight time using this technique is 13 fs.

中文翻译：

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基于 SXFEL 腔监测器的光束到达和飞行时间测量系统优化

为了完全优化高增益自由电子激光器 (FEL) 设施的运行并为时间分辨实验提供机会，需要电子束和种子激光器之间的高精度同步。因此，在上海软X射线FEL（SXFEL）设施中建立了高精度和高分辨率的波束到达和飞行时间测量系统。对于 SXFEL，需要优于 100 fs 的波束到达时间分辨率。SXFEL 已经采用了用于该测量的基于相位腔的检测方案。为进一步优化系统性能，分析了时钟抖动、触发抖动、信号分析长度对测量不确定度的影响，并对相关子系统进行了相应的升级和优化。成功测量波束到达时间，初始测量不确定度优于 45 fs。此外，实现了双腔混合方案来测量光束飞行时间或伪光束到达时间，使用该技术的光束飞行时间测量分辨率为13 fs。