Seeding of sparc-fel with a tunable fibre-based source

TLDR: In this paper, the first results on seeding the SPARC-FEL with a fiber-based tunable ultraviolet source are presented, which consists of a kagome hollow-core photonic crystal fiber (HC-PCF) filled with noble gas.

Abstract: Instead of seeding a free electron laser in the UV-VUV with a frequency doubled or tripled laser or high order harmonics, here we investigate and present the first results on seeding the SPARC-FEL with a fibre-based tunable ultraviolet source. The seed generation system consists of a kagome hollow-core photonic crystal fibre (HC-PCF) filled with noble gas. Diffraction-limited DUV pulses of > 50 nJ and fs-duration which are continuously tunable from below 200 nm to above 300 nm are generated. The process is based on soliton-effect selfcompression of the pump pulse down to a few optical cycles, accompanied by the emission of a resonant dispersive wave in the DUV spectral region. The quality of the compression highly depends strongly on the pump pulse duration, and ideally, pulses < 60 fs should be used. Our experimental set-up and associated GENESIS simulations enable us to study the utility of the seed tunability, and the influence of the seed quality, on the performance of the SPARC-FEL in the 200-300 nm range. Single-pass free-electron lasers (FELs) can be used to generate powerful short pulses at very short wavelengths. Moreover, when seeded with an appropriate pulse, the