The coupled rate equations with the spatial overlap effect for four-level passively Q-switched lasers are fully considered. A transcendental equation is derived for the residual fraction of the inversion density after the finish of the Q-switched pulse. Comprehensive calculations for the transcendental equation were executed to attain an analytical function for precisely fitting the residual fraction of the inversion density. With the fitting function, a pedagogical model with the correction for high output coupling is developed to straightforwardly analyze the output pulse energy and peak power. Detailed experiments are carried out to validate the model.

A novel scheme was developed for a diode-pumped passively Q-switched Nd:YVO4/KGW Raman laser at 589 nm with a diode-to-orange conversion efficiency reaching 11.4%. The compact near-concentric cavity was designed to achieve the criterion of good passive Q-switching and to contain a coupled resonator for intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). The dependence of the output performance on the initial transmission of the saturable absorber was explored in detail. Furthermore, the output performance was studied by considering the influence of the pump-to-mode size ratio. By using an initial transmission of 50%, the highest pulse energy and peak power were 110 μJ and 118 kW, respectively, at a pump duration of 40 μs and a pump frequency of 10 kHz.

In this Letter, we experimentally explore the propagation-dependent evolution of generating the pseudo-nondiffracting quasi-crystalline (crystalline) beams based on the multibeam interference. We originally derived an analytical formula to exactly manifest the propagation evolution of interfering multiple beams. With the analytical formula, the formation of quasi-crystalline structures in the focal plane can be explicitly verified. Furthermore, the distance of the effective propagation-invariant region can be verified in terms of experimental parameters. More importantly, we employed the developed formula to confirm the formation of kaleidoscopic vortex lattices by means of numerically computing the propagation-dependent phase singularities.

Efficient diode-pumped passively Q-switched Nd:YVO4 yellow and orange lasers are developed with the pulse pumping scheme and the intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). A Np-cut KGW is exploited in the SRS process to generate the yellow 579 nm laser or the orange 589 nm laser in a selectable way. The high efficiency is achieved by designing a compact resonator to include a coupled cavity for intracavity SRS and SHG and to provide a focused beam waist on the saturable absorber for reaching an excellent passive Q-switching. The output pulse energy and peak power can reach 0.08 mJ and 50 kW for the orange laser at 589 nm. On the other hand, the output pulse energy and peak power can be up to 0.10 mJ and 80 kW for the yellow laser at 579 nm.

In this work, the spatial effects of the pumping and lasing were considered into the coupled rate equations of passively Q-switched lasers for the condition of no saturation in the gain medium. A transcendental equation of energy utilization was derived, and the solution to the equation was approximated by an analytic model developed in previous work. The reflection factor of output coupler with low reflectivity was modified for more accurate output energy evaluations. Experimentally, an end-pumped Nd:YVO4/Cr4+:YAG laser in a concave-plano cavity with output coupling reflectivity ranging from 10% to 92% was demonstrated, and two different pumping spot sizes of laser diode were adopted for validating the developed spatial model. The experimental results showed good agreements with the theoretical calculations.