Excellent Q-switching operations modulated by new two-dimensional (2D) saturable absorber (SA) materials with stable performance is a hot topic in all-solid-state pulsed laser research. In this work, the watt-level high-stability passive Q-switching operation in a solid-state Nd:YVO4 laser utilizing the 2D germanene nanosheets as SA was first realized. The nonlinear optical properties of the germanene nanosheets (Ge-Ns) were characterized by experimental means. The stable Q-switched pulse sequence was acquired with a 60.6 ns narrowest pulse width and a 528.6 kHz maximal repetition rate. The average output power of 0.965 W and the corresponding pulse peak power of 30.12 W are obtained under the pump power of 7 W. The findings of the experiments demonstrate that germanene material has remarkable nonlinear optical properties and can be used as an excellent saturable absorber in the field of optical pulse modulation.

In recent years, layered transition metal sulfides (TMDCs) exhibit excellent nonlinear saturable absorption properties in laser modulations. Nevertheless, few of them are applied to the optimization of optical parametric oscillators (OPOs). In this work, we prepared a 12.5 nm-thickness platinum disulfide (PtS2) saturable absorber (SA) by a combination of electron beam evaporation (EBE) and post-vulcanization method. The nonlinear transmittance is measured, which exhibits the SA characteristic of PtS2 film. The acousto-optic (AO) Q-switch and the prepared PtS2 SA are used to realize the operation of active and passive Q-switched OPO, and the mid-infrared idler pulse with nanosecond width is obtained. By measuring the experimental output results, the optimizations of PtS2 SA to OPO's operation are analyzed, including the stabilization of pulse train by 240%, the compression of idler-light pulse by 59.7%, the improvement of peak power by 198%. As a result, the improvement of nonlinear conversion is attained by 16.9%. The phenomenon may be due to the excellent saturable absorption effect of PtS2 SA to the fundamental light. This paper shows the optimization effect of the prepared layered transition metal sulfide for laser intracavity modulation on the nonlinear frequency conversion process, especially for the improve of nonlinear conversion effect.

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.

In order to investigate the pulse modulation potential of SnSe2 in all-solid-state lasers, an active and passive dual-loss-modulated (APDM) Q-switched and mode-locking (QML) Nd:YVO4 laser was realized by employing an acousto-optic modulator (AOM) and a 5.9 nm thick SnSe2 saturable absorber (SA). The significant pulse compression ability of SnSe2 film was found experimentally, and sub-nanosecond mode-locking pulses with large peak power were obtained. The average output power, pulse energy, and pulse width versus the pump power were measured. With a pump power of 8.5 W, 242 ps mode-locking pulses with a pulse peak power of 231.4 kW were realized successfully. The experimental results also show that the SnSe2-based APDM QML laser has great potential in generating sub-nanosecond pulses with large peak power and high stability.