Shaping broadband ultraviolet pulses in air for sub-10 femtosecond temporal resolution

Characterizing rapid molecular motion such as electronic wavepackets and proton vibrations requires generating few-femtosecond pulses with sufficient optical bandwidth and dispersion management. Resonant dispersion wave (RDW) emission in hollow capillaries has gained popdularity due to its wavelength tuning functionality and broadband spectra in the ultraviolet. Although RDW pulses are naturally compressed after exiting the fiber, the dispersion inherent in the fiber exit window and in-air propagation has motivated in-vacuum pulse delivery for experiments. We demonstrate that compression of RDW pulses in air using an ultraviolet pulse shaper consisting of an acousto-optic modulator (AOM) in a 4f optical system can achieve ~10 fs pulse durations between 270 nm and 340 nm with microjoule pulse energies. Using an AOM for dispersion management offers several advantages over traditional methods like chirp mirrors; the AOM shaper is completely tunable for a wide range of wavelengths, compensates for higher order spectral phase, and can be used to generate arbitrary pulse sequences. The combination of RDW emission and an AOM pulse shaper to produce ultrashort UV pulses offers opportunities for applications in time-resolved spectroscopy and nonlinear optics.