NEAR-TRANSFORM-LIMITED VISIBLE AND NEAR-IR FEMTOSECOND PULSES FROM OPTICAL PARAMETRIC AMPLIFICATION USING TYPE-II BETA-BARIUM BORATE

Type II phase-matched beta-barium berate is used in the first stage of amplification of a white-light continuum in a two-stage optical param etric amplifier pumped by the second harmonic of a regeneratively ampl ified Ti:sapphire laser system operating at 824 nm. Near-transform-lim ited sub-190-fs pulses with microjoule energies are achieved in the si gnal branch, which is tunable from 475 nm to degeneracy. This system e ffectively bridges the wavelength gap between the fundamental and the second harmonic of amplified Ti:sapphire laser systems.