Mode locking of Ti:AI(2)O(3) lasers and self-focusing: a Gaussian approximation

We present an ABCD matrix model showing that self-focusing in the laser rod leads to modifications of the Gaussian beam parameters in cw-pumped Ti:Al(2)O(3) lasers. Stabilization of self-mode-locking should result from these beam perturbations. Experimental measurements of beam modifications supporting this model are presented. The role of gain guiding is studied, and the limitations of the model are discussed.