Generation of femtosecond radiation at 211 nm by femtosecond pulse upconversion in the field of a picosecond pulse

We show that, in the case of sum-frequency mixing, one can alleviate group-velocity mismatch between IR and UV pulses by choosing different pulse widths, thus extending the interaction length of ultrashort pulses within nonlinear crystals. By fifth-harmonic generation with a Nd:glass laser, we demonstrate efficient frequency upconversion of 195-fs 264-nm pulses under the envelope of 0.9-ps 1055-nm pulses in beta-barium berate crystal, yielding <270-fs pulses with energy of up to 110 mu J at 211 nm. (C) 2000 Optical Society of America OCIS codes: 190.0190, 190.2620, 190.7220, 320.7110.