Femtosecond parametric amplification in the mid-infrared using group matched noncollinear interaction

Summary form only given. The importance of the noncollinear processes was noticed in the first experiments with femtosecond pumping a traveling wave optical parametric generator, where the higher parametric gain was attributed to the lower group velocity mismatch (GVM). This was later utilized when pumping BBO crystals near 400 nm by the second harmonic of femtosecond Ti:sapphire regenerative amplifiers. We demonstrate that the advantages of noncollinear interaction in femtosecond optical parametric generators and amplifiers (OPAs) are not restricted to UV pumping but are a general property that can be utilized in the mid-infrared (MIR) region, too. In previous work the low GVM in MgO:LiNbO/sub 3/ for a certain pump wavelength range near /spl lambda//sub p/=817 nm (collinear group matching) allowed us to achieve extremely high conversion efficiencies and output energies in the femtosecond regime, and to generate extremely short MIR pulses of 5 optical cycles, however, with restricted tunability. In the work we show first by calculations that matching of the group velocities in MgO:LiNbO/sub 3/ can be achieved also for pump wavelengths below 800 nm using noncollinear propagation. We verify then this experimentally by pumping near 780 nm and producing pulses of higher energy and shorter duration in the MIR near 3 /spl mu/m than in the collinear case.