Sub-picosecond green-pumped OPG/OPA using non-critical phase matching in LBO was investigated at high average powers, utilizing a novel high-power ultrafast fiber laser providing 300W of 1ps pulses at 515nm and 1.4GHz pulse repetition rate. The 4-stage collinear OPA produced about 100W of combined Signal plus Idler output powers when tuning the Signal wavelength between 740nm and 940nm. An extended spectral tuning range between 300nm and 1800nm with average power between 10W and 70W was demonstrated by using SFG of Signal plus Pump and SHG of Signal and of Idler. The OPA output pulse durations were ~0.5ps long.
BiB3O6 (BIBO), the first low-symmetry (monoclinic class 2) inorganic nonlinear crystal that became commercially
available, possesses some unique advantages for applications in ultrafast laser technology which are primarily related to
its dispersive properties. In the present paper, these properties are analyzed in more detail and compared with other
crystals. Of special interest is the pumping of this material near 800 nm for broadband parametric amplification in the
near-infrared between 1.15 and 2.4 μm. We present experimental results on generation and amplification of
ultrabroadband femtosecond continua in this spectral range using amplified Ti:sapphire lasers as pump sources.
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.
Analytical formula using elementary functions for the description of the process of nonlinear phase shift of the fundamental waves involved in second harmonic generation or sum frequency mixing have been derived. The analytical results can be used for the design of devices based on cascade second order nonlinear phase shift. Using this formula it is shown that the system 'polarizer-Type II SHG crystal-analyzer' possesses pulse compression capability.
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