Analysis of electro-optical intensity modulator for bunch arrival-time monitor at SXFEL

A bunch arrival-time monitor (BAM) based on an electro-optical intensity modulation scheme is currently under development at Shanghai Soft X-ray Free-Electron Laser to meet the high-resolution requirements for bunch stability. The BAM uses a radio frequency signal generated by a pickup cavity to modulate the reference laser pulses in an electro-optical intensity modulator (EOM), and the bunch arrival-time information is derived from the amplitude change of the laser pulse after laser pulse modulation. EOM is a key optical component in the BAM system. Through the basic principle analysis of BAM, many parameters of the EOM are observed to affect the measurement resolution of the BAM system. Therefore, a systematic analysis of the EOM is crucial. In this paper, we present two schemes to compare and analyze an EOM and provide a reference for selecting a new version of the EOM.