中文摘要：

电子束团纵向长度是束流诊断中的重要参数,电光频谱解码法（Electro-Optical Spectral Decoding,EOSD）是为数不多的可进行单发测量的高时间分辨率测量方法。本文基于上海深紫外自由电子激光装置（Shanghai Deep Ultraviolet Free Electron Laser,SDUV-FEL）设计了一套电光频谱解码法测量束团长度实验方案。通过采用针尖粗同步和可调的光栅展宽器可实现长度在1-10 ps内变化的束团无损测量。通过对电光调制过程及其后探测的仿真研究表明,选用0.5 mm厚的Zn Te晶体在距离束流中心3-5 mm处测量时,时间分辨率最高可达180 fs（Root Mean Square,RMS）,信号展宽在3%以内,测量的电场形状无可观测畸变,满足SDUV-FEL的实验需求。

英文摘要：

Background： The longitudinal length of electron bunch is an important parameter in beam diagnostics. Electro-Optical Spectral Decoding （EOSD） is one of the few powerful approaches to accurately measure bunches down to sub-picosecond level. Purpose： This study aims to design and evaluate a complete system to measure the bunch length at Shanghai Deep Ultraviolet Free Electron Laser （SDUV-FEL）. Methods： The EOSD with a probe used for coarse synchronization and a tunable grating pair used as laser stretcher was designed, and the processes of Electro-Optical modulation and detection were simulated in detail. Results： The bunch length varying from 1 ps to 10 ps can be measured without beam destruction in the whole process. The time resolution （Root Mean Square, RMS） is expected up to 180 fs at best and signal broadening within 3%. Conclusion： The longitudinal bunch length can be measured with high quality utilizing our EOSD setup. The system can meet the demands of SDUV-FEL.