Generation of femtosecond extreme ultraviolet pulses using low-energy electron beams for a pump-probe experiment

Abstract

The surface recombination process and molecular dynamics are generally on the order of tens of femtoseconds; therefore, the research and development of an accelerator-based intense and short-pulse generation scheme are needed for pump-probe experiments, which are widely utilized tools for investigating fast molecular dynamics. Here, we propose an echo-enabled harmonic generation (EEHG)-technique-based free electron laser (FEL) scheme that uses a low-energy beam (KE similar to 200 MeV). The proposed scheme is designed to generate short-pulse soft extreme ultraviolet radiation at - similar to 80 nm, with a pulse duration of 3 fs for the full width at half maximum. An electron injector consisting of a photo-cathode-based S-band radio frequency electron-gun, solenoid magnets, and three S-band accelerating columns was designed and optimized using a multiobjective particle swarm optimization method. For the EEHG-FEL section, the narrow bands of electrons produced by a second modulator and a few-cycle laser pulse with a linear momentum compaction at the second chicane had a perfect upright position at the top of the current modulation produced by the first modulator, which enhanced the peak current by a factor of approximately 30 %. In this scheme, two conventional lasers with wavelengths of 5.2 mu m and 800 nm were adopted to enhance the high bunching factors by generating microbunching structures. The saturated output power of the proposed FEL was approximately 4.97 MW.