Sub-20-fs pulse generation in the ultraviolet

Summary form only given. We report the generation of ultrashort ultraviolet (UV) pulses using nonresonant third-harmonic conversion of a 22-fs driving pulse in a gas. In order to generate ultrafast UV pulses via harmonic generation, it is preferable to use gases rather than crystals such as BBO (beta-barium borate). This is because complications such as finite phase-matching bandwidths and temporal walk-off, which place limits on the UV pulsewidth, can be avoided by using gases. For these experiments, a l-mJ pulse at a wavelength of 800 nm, and with a bandwidth of 38 nm, was focused in air and in various gases to generate the third-harmonic light. Conversion efficiencies of /spl sim/0.1 % from fundamental third-harmonic light were observed, thus generating /spl mu/J level UV pulses. Higher conversion efficiencies were observed in argon. We also observe 40 % higher output power in the third harmonic when the excitation pulse is negatively chirped to /spl sim/40 fs.