We report on efficient mid-IR difference-frequency generation (DFG) at ~8 μm in orientation-patterned GaAs (OPGaAs), by mixing the signal and idler fields inside a nanosecond, singly-resonant, periodically-poled MgO-doped LiNbO3 optical parametric oscillator (OPO). The temperature and spectral acceptance bandwidths as well as the DFG output performance are compared for two OP-GaAs samples with different lengths. Temperature tuning of the DFG is studied by implementing a transversely chirped Volume Bragg Grating (VBG) as one of the OPO cavity mirrors for the signal wave. The maximum DFG average power amounts to 215 mW at 8.15 μm for a pulse repetition rate of 35 kHz. The corresponding overall optical conversion efficiency from 1 to 8 μm is ~1.1%.
The exceptional power scalability of Yb lasers has enabled the development of pulsed optical parametric amplifiers (OPA’s) operating at the short-wave edge of the mid-IR (MIR) with average powers beyond 10 W simultaneously providing peak powers in excess of 1 GW. Further wavelength extension into the longer-wave MIR is enabled by novel wide-bandgap non-oxide nonlinear crystals that can be pumped directly at 1 μm without detrimental one- and twophoton absorption of pump radiation. Eliminating the usual difference frequency generation step in producing MIR pulses above 5 μm could potentially increase the conversion efficiency of parametric down-conversion devices and enable a significant boost in the attainable average and peak power. Despite their utmost importance, material properties related to ultrafast laser-induced damage in nonlinear crystals are rarely investigated in the corresponding laser parameter range. In order to help unravel the complicated interplay of photorefractive effects, thermal lensing, and selffocusing/ defocusing affecting the beam quality and catastrophic breakdown threshold in MIR OPA’s, we present the nonlinear index of refraction at 1 μm of KTiOAsO4, LiGaS2, and BaGa4S7. The reported data provide crucial design parameters for the development of high-average-power MIR OPA’s. As examples, (i) a 100-kHz, 1.55/3.1 μm dual-beam OPA delivering multi-GW peak power in each beam and a total average power of 55 W and (ii) a 100-kHz, sub-100-fs, 1-μm-pumped OPA tunable in the 5.7-10.5-μm range are briefly presented.
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