Nonlinear mode coupling in a microchip laser

The dynamics of the total intensity and of each individual mode of a microchip laser have been studied. Because of the nonlinear mode coupling by spatial hole burning, the intensity fluctuation of each longitudinal mode can be described by N relaxation frequencies, where N is the number of lasing modes. Owing to the small cross-saturation coefficient between the longitudinal modes, the total intensity exhibits a behavior much more complex than the regular relaxation oscillations usually observed. As a result of the short photon lifetime of the microchip laser this unstable behavior of the total intensity can easily be observed even when the number of modes is small. For each longitudinal mode, Re also observed beating and antiphase dynamics between two coupled states of orthogonal polarization. Numerical simulations permit a good description of the experimental results. (C) 1996 Optical Society of America.