We present updated Sellmeier equations for CdGa2S4 that reproduce well the phase-matching angles for Yb:KGd(WO4)2 and Cr:forsterite femtosecond-amplifier-pumped Hg0.35Cd0.65Ga2S4 optical parametric amplifiers (OPAs) and a Ti:Al2O3 femtosecond-amplifier-pumped Hg0.51Cd0.49Ga2S4 OPA in the 5.6–11.5 μm range, when combined with our previously derived Sellmeier equations for HgGa2S4.
Nonlinear vibrational and strong-field spectroscopies can tremendously benefit from high-power few-cycle mid-infrared (MIR) laser pulses beyond 5 μm at repetition rates << 10 kHz. Here, we explore the potential of a novel non-oxide crystal, BaGa4S7 (BGS), for the direct coverage of the MIR beyond 5 µm starting from Yb-laser sources and report on a μJ-scale, sub-4-cycle, 100-kHz optical parametric amplifier (OPA) at 10 μm. We compare BGS with LiGaS2 (LGS) with respect to performance in ultrafast MIR OPAs. The unique properties of BGS indicate great potential for nonlinear optical applications, especially due to the much faster development of its manufacturing processes and the larger achievable single-crystal sizes compared to LGS.
With diode-pumped Yb laser technology reaching maturity, average power scaling of multi-GW, few-cycle, short-wave and mid-infrared (MIR) optical parametric amplifiers (OPA’s) to the 100-W level has become a reality. Well established, commercially available oxide crystals offer a relatively straightforward solution in the 1.4-4-μm spectral range. Extension of the spectral coverage of high-power OPA’s beyond 5 μm may be enabled by novel, wide-bandgap non-oxide crystals with growth processes still under major development and optimization. Here, we present our results on the nonlinear optical properties of oxide (LiNbO3, KTiOAsO4) and non-oxide (LiGaS2, BaGa4S7) crystals and the resulting 100-kHz, ultrafast infrared OPA’s based on these materials. The reported data provide design parameters and guidelines for high-average-power MIR OPA’s pumped by Yb lasers both below and above 5 μm.
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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