Generation of sub-20-fs, two-color deep-ultraviolet pulses by four-wave mixing through filamentation in gases

摘要

Generation of ultrashort pulses at 260 nm and 200 nm by four-wave mixing through filamentation in neon gas was demonstrated. Fundamental (ω_1) and second-harmonic (ω_2) pulses of 25 fs Ti:sapphire laser output were focused into neon gas, and 260 nm (ω_3) pulses were produced by a four-wave mixing process, ω_2 + ω_2 - ω_1 → ω_3, through an ～ 15 cm filament. At the same time, 200 nm (ω_4) pulses were also genereted by a cascaded process, ω_3 + ω_2 - ω_1 → ω_4, and/or by a sum frequency process, ω_2 + ω_1 + ω_1 → ω_4. The both pulses were simultaneously compressed by a grating-based compressor, and characterized by a trangient grating frequency-resolved optical gating. The estimated pulse widths of the 260 nm and 200 nm pulses were 14 fs and 16.5 fs, respectively.