Improvement of reverse-taper enhanced echo-enabled harmonic lasing at SXFEL

The harmonic lasing technique was proposed to extend the harmonic up-conversion number, and a reverse taper undulator was then adopted to enhance the performance of the harmonic lasing process. But in a typical experiment, energy spread always plays an essential role in the exponential gain of a high-gain free electron laser. In this paper, phase shifters are employed at the Shanghai Soft X-ray Free Electron Laser Facility to reduce the damage effect of the energy spread and avoid the degradation of the final FEL performances. Three-dimensional simulations are conducted to verify the feasibility of the phase shifters’ ability to prevent high energy spread and obtain FEL with superior coherence.