The rate equations for the intracavity-frequency-doubled quasi-three-level lasers are developed. By normalizing the related parameters, it is shown that the general solution to the rate equations is de pendent upon four dimensionless parameters: the normalized reabsorption loss, the pump to laser-mode size ratio, the normalized pump level, and a parameter written as nSHG, which is related to the ability of the nonlinear crystal to convert the fundamental to the second harmonic. By numerically solving these rate equations, a group of general curves are obtained to express the relations between the solution and the four dimensionless parameters.

The intracavity photon density and initial populationinversion density in the diode-pumped actively Q-switched laserrate equations are assumed to be Gaussian distributions. Thesespace-dependent rate equations are solved numerically and agroup of general curves are generated. By using these curvesand the related formulas, the pulse parameters of an arbitraryactively Q-switched laser can be easily estimated and an optimallycoupled Q-switched laser can be designed. A sample calculationfor a Q-switched Nd3+:YVO4 laser is presented to demonstratethe use of the curves and the related formulas.

The absorption spectrum of a new crystal Nd:Srs(PO4)3F (Nd:S-FAP) was measured and its strong absorption peak at 805.4nm showed that it can be suitably pumped with a laser-diode. By using a laser-diode pump operating at 805.4nm, Nd:S-FAP has been successfully lased at 1.059um. A slope efficiency of 37.5% and a laser threshold of only 13mW have been measured, and the theoretical prediction is in agreement with the experimental result.

The absorption spectrum of a new crystal, Nd:Sr5sVO4d3F (Nd:S-VAP), was measured, which showed thatNd:S-VAP can be suitably pumped at 583.0 and 809.0nm as well as with a xenon flash lamp. With atunable dye laser (570-600nm) and a xenon flash lamp as pump sources, respectively, the free-running andQ-switched outputs with BDN dye film were realized at 1.065mm. For the tunable dye-laser pump sourcethe threshold energy is 2mJ and the slope eff iciency is 50%, while for the xenon f lash-lamp pump source thelowest threshold energy is 130mJ and the highest slope efficiency is 1.3%. The laser characteristics, such asthe emission spectrum, the polarization, the output energy, and the pulse width, were measured. In addition,the prospect of a Nd:S-VAP crystal for low-threshold, high-eff iciency miniature lasers is discussed.