Ultraviolet pulse compression via cross-phase modulation in a hollow-core fiber

The generation of few-femtosecond pulses with high energy and tunable spectrum in the ultraviolet region is an ongoing challenge in ultrafast optics. Harnessing the cross-phase modulation between an intense near-infrared pulse and its third-harmonic, co-propagating in a gas-filled hollow-core fiber, we demonstrate spectral tuning, broadening, and temporal compression in the ultraviolet range. Ultraviolet pulses with negative chirp, leading to self-compression down to 6 fs during propagation in air, and energy >10µJ were characterized. This technique opens a way towards the realization of few-fs pulses with high energy, tunable over most of the ultraviolet range.