Self-focusing-induced saturable loss for laser mode locking

Self-focusing has recently been used for fast saturable absorber mode locking and femtosecond pulse generation in Ti:Al(2)O(3) lasers. We describe the operation, design, and optimization of self-focusing loss modulators for mode locking. A new formalism is developed that simplifies the treatment of self-focusing in thick nonlinear media by using a simple transform of the complex Gaussian beam parameter. Theoretical predictions are confirmed by experimental measurements.