Investigations of 2D PtS₂'s Saturable Absorption Characteristic and Its Optimization to OPO's Operation

A 6.2 nm-thickness platinum disulfide (PtS₂) film was prepared by electron beam evaporation with post vulcanization. The nonlinear transmittance was measured by power scanning method and the modulation depth is fitted to be 13%. Based on the transmittance curve, saturable absorption parameters of PtS₂ are calculated with inhomogeneously broadening mechanism, including 6.4298 × 10^-19 cm^-2 ground-state absorption cross-section, 2.5927 × 10^-19 cm^-2 excited-state absorption cross-section, and 1.043 ms excited-state lifetime. The PtS₂ film combined with active time management was implemented to modulate the fundamental light of optical parametric oscillator (OPO). Owing to the nonlinear absorption property of PtS₂, the operation of Q-switched OPO was optimized in both the experiment and dynamical theory. In particular, the conversion efficiency was experimentally improved by 13.2%. The pump-to-signal conversion efficiency went up to 3.29%, which is the highest conversion value reported so far. The theoretical values fit the experiment well, which are from the Gaussian rate equations with PtS₂'s saturable-absorption characteristic.