Ultrabroadband phase-matched optical parametric generation in the ultraviolet by use of guided waves

We present what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases. Broad-bandwidth ultrafast pulses, tunable around 270 nm, were generated from an ultrafast Ti:sapphire amplifier system using $2\omega +2\omega -\omega$ parametric wave mixing in a capillary waveguide. We achieved nonresonant phase matching by coupling both the fundamental and the second-harmonic light into the lowest-order mode. The output $3\omega$ pulses have an energy of $>4 \mathit{\mu }\mathrm{J}$ at a 1–kHz repetition rate. Simple extensions of this method can generate higher-energy 10–20-fs pulses tunable throughout the vacuum ultraviolet.