An efficient and tunable 176-550 nm source based on the emission of resonant dispersive radiation from ultrafast solitons at 800 nm is demonstrated in a gas-filled hollow-core photonic crystal fiber (PCF). By careful optimization and appropriate choice of gas, informed by detailed numerical simulations, we show that bright, high quality, localized bands of UV light (relative widths of a few percent) can be generated at all wavelengths across this range. Pulse energies of more than 75 nJ in the deep-UV, with relative bandwidths of ~3%, are generated from pump pulses of a few μJ. Excellent agreement is obtained between numerical and experimental results. The effects of positive and negative axial pressure gradients are also experimentally studied, and the coherence of the deep-UV dispersive wave radiation numerically investigated.

Tunable vacuum-UV to visible ultrafast pulse source based on gas-filled Kagome-PCF

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

K. Mak

Papers

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