中文摘要：

高获得的泛音产生(HGHG ) 的串联阶段释放电子激光(FEL ) 是生产充分协调的 X 光检查放射的一个有希望的方法。作为为现代 FEL R&D 的一台测试设备，上海深紫外的 FEL (SDUV-FEL ) 现在在为串联升级 HGHG 实验的二个阶段下面。因为电子横梁的精力象在升级以后的大约 185 兆电子伏一样低，二阶段 HGHG 的全部的泛音数字仅仅是 2 吗？

英文摘要：

Cascading stages of high-gain harmonic generation （HGHG） free electron laser （FEL） is a promising way to produce fully coher- ent X-ray radiation. As a test facility for modern FEL R＆D, the Shanghai deep ultraviolet FEL （SDUV-FEL） is now under up- grading for the cascading two stages of HGHG experiment. Since the energy of the electron beam is as low as about 185 MeV after upgrade, the total harmonic number of this two stages HGHG is only 2x2, and the wavelength of the final radiation is 196.5 nm which is the 4th harmonic of the 786 nm seed laser. With help of three-dimensional simulation codes, design studies on the FEL physics for the cascaded HGHG experiment are present based on the parameters of the upgraded SDUV-FEL facility. It is found from the simulation results that the part of the electron beam which has been used in the first stage can still generate pow- erful radiation in the radiator of the second stage, and this radiation will be difficult to be separated from the radiation generated by the fresh part of the electron beam. To overcome this problem, a novel method based on the energy spectrum of the electron beam is proposed in this paper to demonstrate the ＂fresh bunch＂ technique.