Modeling a passively Q-switched Nd:YVO₄ laser with an application to spatio-temporal instability

In this study, a numerical model of a passively Q-switched laser system to concerning the transverse distribution of the optical field is presented. Applying this numerical model to examine the dynamics of a passively Q-switched Nd:YVO₄ laser with a Cr⁴⁺-doped yttrium aluminum garnet (Cr⁴⁺:YAG) saturable absorber, a spatio-temporal instability is evident when this laser is operated in the transverse degenerate configuration. The mechanism of instability is mainly governed by the transverse mode competition among the degenerate modes. Results of this study demonstrate that there are two bifurcating branches corresponding to the different spatio-temporal evolutions as the pump power increases. Moreover, each bifurcation is accompanied by the excitation of the higher-order degenerate transverse modes.