Numerical analysis of multi-mode laser with modulated inversion

Abstract

A systematic description is developed for the dynamical behavior of a multi-mode unidirectional ring laser under modulation of the population inversion in a homogeneously broadened active medium. The modulation frequency is chosen to be close to the longitudinal mode spacing in the cavity. We report a rigorous and extensive numerical analysis of this system by choosing the dc component of the population inversion, the modulation amplitude and the detuning of the modulation frequency as control parameters for both cases of good and bad cavities. In the good cavity, this system exhibits two characteristic transitions toward the conventional mode-locked pulse oscillation as the modulation amplitude increases: the first transition to the region of the ordered amplitude and disordered phase of the electric field, and the second one to the ordinary mode-locking in which both the amplitude and the phase are ordered. In the bad cavity, two kinds of chaos are observed: the Lorenz-type chaos in the region of weak modulation and strong population inversion and the quasi-periodic chaos in the region of strong modulation and intermediate population inversion. The dimensionality of chaotic behaviors is also tested to reveal mechanisms of instability. The coherent and incoherent properties of emitted light at each region are clarified, too.