为解决硬X射线自由电子激光装置难以提供皮秒至纳秒区间时间分辨的问题，提出了面向目前在建的上海硬X射线自由电子激光装置分束延迟的系统设计。采用基于晶体衍射的延迟方法设计分束延迟光学系统，计算了延迟时间范围，模拟了系统光通量，搭建了一台样机并进行了光路对准实验。该设计采用空间分光方式，将入射脉冲分为两个部分，并通过路程差在二者之间引入时间延迟，具体的原理样机设计适用于光子能量在7~11 keV范围，最多能实现-15.4~503.3 ps的时间延迟。使用Shadow模拟了样机设计的光通量，两个分支光通量分别为33.54%和33.64%，符合1∶1的设计目标。使用绿光激光进行了样机的光路对准实验，证明该样机能使空间分光后的两束光重新复合，为后续X射线验证实验提供基础。该设计具有空间尺寸小、延迟范围大、入射能量和延迟时间连续可调的优点，为上海硬X射线自由电子激光装置的分束延迟系统研制提供参考。

Owing to their ultra-high accelerating gradients, combined with injection inside micrometer-scale accelerating wakefield buckets, plasma-based accelerators hold great potential to drive a new generation of free-electron lasers (FELs). Indeed, the first demonstration of plasma-driven FEL gain was reported recently, representing a major milestone for the field. Several groups around the world are pursuing these novel light sources, with methodology varying in the use of wakefield driver (laser-driven or beam-driven), plasma structure, phase-space manipulation, beamline design, and undulator technology, among others. This paper presents our best attempt to provide a comprehensive overview of the global community efforts towards plasma-based FEL research and development.

精密定时已成为很多大型先进科学装置的必备技术,而定时精度是这些大型仪器实现其最终目标的关键因素。本文回顾了近年来定时技术的进展,包括不同类型的信号源(激光、微波和X射线脉冲)的定时测量方法,以及基于自由空间链路和光纤的大型定时同步系统。最后简单讨论了目前定时系统的主要限制因素及未来可能的研究方向。

提出了一种基于T形光栅的新型史密斯-珀塞尔自由电子激光器。并利用理论分析和粒子(Particle-in-Cell,PIC)模拟的方法研究了光栅形状对史密斯-珀塞尔自由电子激光器输出特性的影响。理论分析发现,基于T形光栅的史密斯-珀塞尔自由电子激光器的注-波互作用较强,电子束的群聚特性较强,相应地有较强的注-波转换效率,进而有较高的输出功率。PIC模拟发现,基于T形光栅的史密斯-珀塞尔自由电子激光器能够提高辐射功率。在电子束能量E=50 keV、电子束电流i=10 A、光栅周期D=0.3 mm的情况下:基于T形光栅的史密斯-珀塞尔自由电子激光器可以得到0.753949 THz、峰值输出功率约为2 kW的连续太赫兹辐射;而基于矩形光栅的史密斯-珀塞尔自由电子激光器只能得到0.723397 THz、峰值输出功率约为0.3 kW的连续太赫兹辐射。

For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase, and the gun energy. The transverse emittance measured at the Injector Test Facility (ITF) is εx=0.48±0.01 mm mrad. An undulator prototype based on the EU-XFEL design and modified for PAL-XFEL was built and tested. A local-K pole tuning procedure was developed and tested. A significant reduction (90%) of the local-K fluctuation was observed. The requirement of undulator field reproducibility better than 2 ×10₄ and the undulator gap setting accuracy below 1 μm were achieved for the prototype. The optical phase jitter after the pole height tuning at the tuning gap was calculated to be 2:6_ rms, which satisfies the requirement of 5.0_.

The status of the European X-ray Free-Electron Laser (European XFEL), under construction near Hamburg, Germany, is described. The start of operations of the LCLS at SLAC and of SACLA in Japan has already produced impressive scientific results. The European XFEL facility is powered by a 17.5 GeV superconducting linear accelerator that, compared to these two operating facilities, will generate two orders of magnitude more pulses per second, up to 27 000. It can therefore support modes of operation switching the beam up to 30 times per second among three different experiments, providing each of them with thousands of pulses per second. The scientific possibilities opened up by these capabilities are briefly described, together with the current instrumental developments (in optics, detectors, lasers, etc.) that are necessary to implement this program.

提出了波长为λi的入射激光与速度为v0、通过波长为λw周期磁场的电子束背散射产生波长λf激光的方案。只要v0足够大，就有λf远小于λi 。扭摆磁铁覆盖有缝隙的超导片后，λw虽不变，但有效背散射区纵向长度s能显著减小。足够强的入射激光也能使s显著减小。与电子束平行的激光谐振腔能产生强度足够大的入射激光。这样，波长λf激光就能实现。即使出射激光的光子数少于入射激光光子数，出射激光的功率仍可以大于入射激光的功率。

考虑电子束横向发射度和电子β振荡, 将2005年国际上提出的单通过高增益自由电子激光饱和状态分析的统计物理方法发展到三维情形。首先建立一种描述电子三维运动的归一化简化模型, 推导了一维光场下包含电子横向运动的Vlasov方程。在螺旋型波荡器情形下通过引入横向运动守恒量发展了三维统计物理分析方法, 并编写了相应计算程序, 计算自由电子激光达到饱和时系统的光强增益、聚束因子。作为对比验证, 编写包含N个电子自由电子激光系统的三维直接数值模拟程序, 结果表明数值模拟和统计计算结果相一致。对比文献中一维模拟和一维统计理论计算结果, 所得结果反映了电子束横向发射度以及电子在波荡器中的横向β振荡对饱和点参数的影响。