Tunable X-ray frequency comb generation at the Shanghai soft X-ray Free-Electron Laser facility

Abstract

X-ray frequency combs (XFCs) are of great interest in many scientific research areas. In this study, we investigate the generation of high-power tunable XFCs at the Shanghai soft X-ray Free-Electron Laser facility (SXFEL). To achieve this, a chirped frequency-beating laser is employed as the seed laser for echo-enabled harmonic generation of free-electron lasers. This approach enables the formation of an initial bunching of combs and ultimately facilitates the generation of XFCs under optimized conditions. We provide an optical design for the chirped frequency-beating seed laser system and outline a method to optimize and set the key parameters that meets the critical requirements for generating continuously tunable XFCs. Three-dimensional simulations using realistic parameters of the SXFEL demonstrate that it is possible to produce XFCs with peak power reaching 1.5 GW, central photon energy at the carbon K edge (~284 eV) and tunable repetition frequencies ranging from 7 to 12 THz. Our proposal opens up new possibilities for resonant inelastic X-ray scattering experiments at X-ray free-electron laser facilities.

Keywords

• chirped frequency beating
• echo-enabled harmonic generation
• free-electron laser
• optical frequency combs