ACCURATE SYNCHRONIZATION BETWEEN SHORT LASER PULSE AND ELECTRON BUNCH BY USING HGHG OUTPUT AT 266NM AS PHOTOCATHODE LASER FOR RF GUN.

摘要

Synchronization between seed laser pulse and electron bunch to below 50 fs is a critically important issue in carrying out cascading HGHG stages to achieve intense temporally coherent x-ray FEL. The single stage HGHG experiment in the IR and recently in UV region has achieved significant success. Hence the next step, to demonstrate the cascading of 2 stages of HGHG becomes crucially important in confirming the viability of this scheme. Based on our experiences at DUVFEL during the HGHG experiment, we can measure the time jitter between the electron bunch and the RF phase before compression to a high precision of order of 50 fs. Without the compression, this is equal to the time jitter between the laser and the RF phase. An analysis of this measurement suggests that it is possible to use a fast feedback system to reduce the jitter significantly. However, during the successful HGHG experiment at 266 nm recently, we realized that there is a simpler way to achieve highly accurate synchronization. Here we describe the method.