CHIRP-TAPER COMPENSATION IN LWFA-DRIVEN FREE-ELECTRON LASERS FOR ENHANCED LASER-BEAM SYNCHRONIZATION

Shan-You Teng^1,2*, Wai-Keung Lau², Shih-Hung Chen¹, Wei-Yuan Chiang²

¹Physics, National Central University, Taoyuan, Taiwan
²Linac, National Synchrotron Radiation Ressearch Center, Hsinchu, Taiwan

* Presenter:Shan-You Teng, email:awdrgy012311@gmail.com

We present a comprehensive three-dimensional simulation for laser-plasma-based high-gain free electron lasers (FELs). Laser wakefield accelerators (LWFAs) can generate electron beams with high peak current and low emittance, but their intrinsic energy spread, typically at the level of a few percent, remains a critical limitation for FEL applications. To address this issue, a 4-dipole energy compressor is employed to reduce the slice energy spread of the electron beam, ensuring that the beam meets the requirements for high-gain FEL operation. However, the overall FEL performance remain constrained by the correlated energy chirp after the energy compressor. To further enhance the FEL efficiency, we investigate the application of a longitudinally tapered undulator in SASE and seeded configurations. By properly tailoring the undulator parameter along the beam propagation, phase synchronization between the energy-chirped electron beam and the radiated field can be restored. Our simulations demonstrate that the tapering scheme compensates for the effects from residual energy chirp, leading to improved radiation power and enhanced spectral brightness. The results highlight a viable pathway for bridging the gap between current LWFA beam quality and the stringent requirements of high-performance FELs, offering a promising route toward compact, plasma-based coherent light sources.

Keywords: Free electron lasers, laser plasma accelerator, high gain harmonic generation