Active plasma lens based beamline for chromaticity-tolerant compact free-electron lasers

As laser wakefield acceleration (LWFA) progresses, the prospect of compact free-electron lasers (FELs) in the extreme ultraviolet (EUV) becomes increasingly feasible. Despite successful demonstrations of coherent FEL sources driven by LWFA, achieving stable high-gain FEL output remains a significant challenge due to insufficient electron stability. In this study, we have designed a beam transport system using an active plasma lens (APL) for LWFA-driven FEL in the EUV regime. Through start-to-end simulations, we achieved a radiation energy of 7.2 μJ and a peak power of 3.2 GW at 13.5 nm. Moreover, the output remained above 1 μJ even with a bunch energy jitter of -7% to +9%, greatly enhancing the chromaticity tolerance of a future compact FEL source. We further investigated the forces experienced by electrons within the APL and the emittance evolution, and provided the FEL radiation gain process of the APL-based beamline. This APL-based beamline scheme is expected to significantly improve the performance of LWFA-driven FELs, and will enable prospects for widespread applications.