近些年，基于先进加速器的高增益自由电子激光（FEL）受到了国际上的广泛重视和大力发展。FEL具有极高的时间和空间分辨率，能为多种科学研究开辟全新的领域。双色FEL是近年来在高增益FEL领域迅速兴起的一项前沿技术，可用于对物理、化学中的基本过程进行深入的研究。目前国际上所有的高增益FEL装置都在着力开展双色FEL产生的相关研究。本项目结合国际上FEL的发展趋势，拟通过理论与模拟研究，对双色FEL产生机制进行全面的探索，并对一些新型的双色FEL产生机制进行深入研究；另外，我们还将基于上海软X射线FEL试验装置（SXFEL）开展双色FEL关键技术的研究，搭建开展双色FEL实验所需的光学系统。本项目的目标是提出全相干X射线双色FEL产生的新机制，满足FEL用户的各种需求，同时掌握双色FEL产生的关键技术，为SXFEL开展双色FEL实验奠定基础。

In recent decades, the high-gain free-electron lasers (FELs) based on advanced accelerator techniques have been successfully developed around the world. High-gain FELs hold the ability for the generation of coherent radiation pulses with ultra-short time duration at high photon energies, which capable of enabling new areas of sciences. Generating two-color radiation pulses with ultra-short pulse durations is of remarkable interest in the FEL user community. Applications exist over a broad range of wavelengths involving pump-probe experiments, which can be used to investigate the ultrafast process occurring during chemical and physical reactions. Nearly all high-gain FEL facilities around the world have performed the two-color FEL experiments in recent years. Here the applicant and his collaborators propose to study the mechanisms of various two-color FEL schemes and develop key technologies for two-color FEL experiments at the Shanghai soft x-ray test facility (SXFEL). It is hoped that several novel two-color x-ray FEL generation schemes will be proposed to satisfy the new demands of FEL users and optical systems will be built for the two-color FEL experiments at SXFEL through the studies of this proposal.