Generation of 12 fs deep-ultraviolet pulses by four-wave mixing through filamentation in neon gas

Generation of deep-ultraviolet femtosecond pulses by four-wave mixing through filamentation in neon gas was demonstrated. Fundamental $\left(\omega \right)$ and second-harmonic $\left(2\omega \right)$ pulses of $25\mathrm{fs}$ Ti:sapphire amplifier output were focused into neon gas, and $20\mathrm{\mu }\mathrm{J}$ pulses with the center wavelength of $260\mathrm{nm}$ were produced by a four-wave mixing process, $2\omega +2\omega -\omega \to 3\omega$ through an $\sim 15\mathrm{cm}$ filament. Additionally, pulses with an energy of $2\mathrm{\mu }\mathrm{J}$ at $200\mathrm{nm}$ were generated, probably by a cascaded process, $3\omega +2\omega -\omega \to 4\omega$. The $260\mathrm{nm}$ pulses were compressed by a grating-based compressor and characterized by a dispersion-free transient grating frequency-resolved optical gating. The estimated pulse width was $12\mathrm{fs}$.