AUTHOR=Zhang Baichao , Li Xiaoshen , Liu Qi , Zhu Zexiu , Zhang Weiqing , He Zhigang , Liu Wei , Wu Guorong , Yang Xueming 

TITLE=High repetition-rate photoinjector laser system for S3FEL

JOURNAL=Frontiers in Physics

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1181862

DOI=10.3389/fphy.2023.1181862

ISSN=2296-424X

ABSTRACT=<p>The photoinjector laser system of Shenzhen Superconducting Soft X-Ray Free Electron Laser (S<sup>3</sup>FEL) is reported in this paper. This laser system operates at up to 1 MHz and produces more than 50 <italic>μ</italic>J infrared (IR) laser pulses. With a customized fourth harmonic generation (FHG) module, more than 2 <italic>μ</italic>J ultraviolet (UV) laser pulses were obtained. The power standard deviations of the IR laser and the UV laser are 0.093% and 0.395% respectively. While the pulse energy standard deviations are 1.087% and 1.746% correspondingly. We implemented the pulse stacking scheme to generate flat-top pulses. With four birefringent uniaxial crystals, the Gaussian pulses were converted to flat-top shape, featuring 10 ps pulse width and 0.5 ps rising and falling edges. A cut-Gaussian transverse profile with very sharp rising and falling edges can be produced after the spatial pulse shaper.</p>