Bright, Tuneable and Compact Source of Few-Femtosecond Pulses in the Deep Ultraviolet

Tuneable ultrashort pulses in the vacuum ultraviolet (VUV, 100-200 nm) and deep ultraviolet (DUV, 200-300 nm) are a vital tool for next-generation ultrafast spectroscopy, technology, and medicine. Resonant dispersive wave (RDW) emission in gas-filled hollow-core waveguides is uniquely placed to fulfill this requirement, delivering continuously tuneable VUV and DUV laser pulses with high efficiency, few-femtosecond duration, and near-perfect beam quality [1] , [2]. Ultraviolet RDW emission in small-core anti-resonant fibres at low pulse energy and high repetition rate can generate Watt-level average powers [1]. However, this approach requires highly specialised waveguides, suffers from guidance resonances which impede fully continuous tuneability and VUV generation, and is ultimately limited in average power due to plasma build-up effects which cap the pulse repetition rate [3]. At much higher pulse energy, simple large-core hollow capillary fibre (HCF) can be used for RDW emission [2] , but this has so far only been demonstrated using large research-grade ultrafast laser amplifiers.