Optical parametric generation of high-energy femtosecond pulses in the 1-3 &mgr;m spectral range using BiB3O6

We analyze the phase-matching properties of the monoclinic nonlinear crystal BiB3O6 (BIBO) for optical parametric amplification of femtosecond pulses when pumped near 800 nm by Ti:sapphire based laser systems. BIBO possesses higher figure of merit than &bgr;-BaB2O4 (BBO) and extremely large parametric gain bandwidth for collinear interaction. Experimentally, we compare type-II BIBO and BBO in a double pass optical parametric amplifier (OPA), pumping by amplified 80-fs pulses near 800 nm at a repetition rate of 1 kHz. The conversion efficiency obtained with BIBO is higher and a total energy output (signal + idler) of about 80 &mgr;J is obtained in the plateau region of the tunability curve (1-3 &mgr;m) with an uncoated sample, for a total pump energy of 375 &mgr;J. Shorter pulse durations were obtained with BIBO: e.g. 120 fs (FWHM) near 3 &mgr;m for the idler pulses. Substantial power scaling of such a femtosecond OPA is possible using a large aperture BIBO crystal in the second stage and we demonstrate a total energy output (signal + idler) exceeding 1 mJ, corresponding to an intrinsic conversion efficiency of ≈32% for the second stage, using a specially designed high-power Ti:sapphire pump system operating at 1 kHz. The tunability extends in this case from 1.1 to 2.9 &mgr;m. The high parametric gain and broad amplification bandwidth of type-I BIBO allow the maintenance of the pump pulse duration, leading to pulse lengths less than 140 fs, both for the signal and idler pulses, even at such high output levels.

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