Transverse pattern formation of optical vortices in a microchip laser with a large Fresnel number

We experimentally investigate the dependence of the transverse pattern formation in a solid-state microchip laser on the Fresnel number. Controlling the transverse-mode spacing and the mode size can generate the stable transverse pattern of optical vortex lattices. A spontaneous process of transverse-mode locking within almost-degenerated mode families is found in the formation of vortex lattices. The frequency of self-induced oscillation in vortex lattices agrees well with the previous theoretical prediction.