Optimising Resonant Dispersive Wave Generation in Hollow Capillary Fibre for Few-Femtosecond Soft X-Ray Transient Absorption Spectroscopy

Achieving few-femtosecond resolution for a pump-probe experiment is crucial to measuring the fastest electron dynamics. As almost all molecules resonantly absorb radiation in the UV and/or visible, generating ultrashort pump pulses in this part of the optical spectrum has huge potential for probing excited state electronic dynamics while not ionising the molecule or material. However, traditional UV-Vis pump pulses cannot achieve few-fs durations and usually operate at fixed wavelengths. Almost every material and even air begin to be absorbent and highly dispersive in this region, making the generation, transport, and characterisation of ultrashort UV pulses extremely challenging. Technology to produce few-fs widely tuneable UV pulses was recently realised by the generation of resonant dispersive wave (RDW) emission in gas-filled hollow capillary fibres (HCF) [1]. RDW is a revolutionary new way to pump photochemical systems that overcome many limitations of traditional pumping regimes.