The development of 3D electron bunch monitor with femtosecond resolution

3D-BCD监测器可以同时对纵向和横向BCD进行无损测量。我们在SPring-8光注入测试加速器上用多个EO晶体验证了这种横向检测。在高次谐波（HH） FEL播种中，需要最大限度地保持HH激光脉冲与电子束之间的6d相空间重叠。我们构建了一个基于eo采样的相对定时漂移监测器，利用hh驱动脉冲和eo探测脉冲的共同外部激光源，测量了hh激光脉冲与电子束的定时差异。我们的反馈系统将EO信号的峰值波长保持在相同的波长，在先导用户实验中提供了命中率为20-30%的种子FEL脉冲。为了达到时间分辨率的上限，我们开发了高时间响应eo探测器晶体和线性啁啾率为1 fs/nm（平顶光谱）的倍频宽带探测激光脉冲。

3D-BCD monitor enables non-destructive measurements of the longitudinal and transverse BCD at the same time. We verified this transverse detection with multiple EO crystals at SPring-8 photoinjector test accelerator. In the high-order harmonics (HH) FEL seeding, it is required to maximize and keep 6D-phase-space overlapping between HH-laser pulse and electron bunch. We constructed a relative timing drift monitor based on EO-sampling, which measured the timing differences between the seeding HH-laser pulse and the electron bunch, using a common external laser source of both HH-driving and EO-probing pulses. Keeping the peak wavelength of EO signals at the same wavelength with our feedback system, we provided seeded FEL pulses with a 20-30% hit rate during pilot user experiments. For achieving the upper limit of temporal resolution, we developed high-temporal-response EO-detector crystals and an octave broadband probe laser pulse with a linear chirp rate of 1 fs/nm (flattop spectrum).