Direct temporal characterization of ultrashort ultraviolet pulses generated via resonant dispersive wave emission in gas-filled capillaries.

Few-femtosecond ({1 {fs}=10^$-15 {s}$) pulses in the deep and vacuum ultraviolet (DUV/VUV) spectral regions are very attractive sources for ultrafast molecular spectroscopy. However, their generation and exploitation have traditionally been very difficult, due to the lack of suitable broadband nonlinear materials and dispersion management at these wavelengths. Recently, the generation of tuneable, broadband (Fourier transform limit time duration (FTL) below $3 {fs}$) DUV/VUV pulses with $\mu J$-level pulse energy via Resonant Dispersive Wave emission (RDW) in hollow capillary fibers has been demonstrated. Here, we present the direct temporal characterization of DUV pulses generated via RDW. The generated $\mu J$-level pulses, with central wavelength (CWL) ranging from 230 to $320 {nm}$ (FTL ranging from 3 to $4 {fs}$) are temporally characterized in a home built all-in-vacuum Self-Diffraction Frequency-Resolved Optical Gating setup. The measured full-width half-maximum time duration, for a pulse with CWL of $280 {nm}$, is $5.4 \pm$ 1.7 ${fs}$. The source could be readily exploited for DUV ultrafast molecular spectroscopy applications with unprecedented tunability and temporal resolution.