Mid-infrared femtosecond optical parametric generator pumped by a Cr:forsterite regenerative amplifier at 1.25 /spl mu/m

Summary form only given. Optical parametric generators (OPG) and amplifiers of the traveling wave type for frequency transformation of high power femtosecond pulses were based up to now exclusively on Ti:sapphire laser technology. The upper wavelength limit for the idler wave is about 3 /spl mu/m for the most widely used nonlinear crystal, BBO, and could be extended with more sophisticated techniques up to about 4 /spl mu/m by using KTP or its isomorphs, KNbO/sub 3/, and MgO:LiNbO/sub 3/. However, not only the upper transparency cut-off of about 5 /spl mu/m, but also the increasing group velocity mismatch (GVM) prevents going to even longer mid-IR wavelengths with all these crystals. Other non-linear optical crystals that are more transparent in the mid-IR like AgGaS/sub 2/ (up to 12 /spl mu/m) and GaSe (up to 18 /spl mu/m), however, cannot be pumped near 800 nm, because of the two-photon absorption. Consequently in the femtosecond regime they can be used only in cascaded difference-frequency generation schemes, that have in general low conversion efficiencies and provide only low output energy. We report for the first time to our knowledge on an AgGaS/sub 2/-based OPG, pumped at 1 kHz by a Cr:forsterite regenerative amplifier tuned to 1.25 /spl mu/m. Since the band-edge of AgGaS/sub 2/ is at 450 nm, two-photon absorption is absent and broad mid-IR tunability can be achieved.