Nonlinear absorption and parametric gain interaction in green-pumped subnanosecond MgO:PPLN OPG

We report on optical parametric generation in a 532 nm-pumped periodically poled MgO-doped LiNbO₃ (MgO:PPLN) crystal operating in the subnanosecond regime at GW/cm²-level peak pump intensities. Within the 690 - 2300 nm tunable Nd:YAG microlaser-based optical parametric generator (OPG), a pronounced nonlinear absorption for 532 nm wavelength was observed. Despite significant light-induced absorption losses, the OPG achieved μJ-level output energies with up to 62% conversion efficiency. We show that by pumping the OPG in an off-axis geometry, it is possible to exploit the QPM grating edge effect to tailor the pump intensity-dependent spatial and spectral properties of the output, resulting in reduced non-collinear QPM interaction and a twofold decrease in the far-field divergence of the signal and idler waves. A comprehensive numerical model was developed which qualitatively explained the observed OPG behavior. The achieved output parameters position the 532 nm-pumped MgO:PPLN OPG as an attractive seed source for subnanosecond optical parametric amplification in the visible spectral range.