Vectorial equations and polarization characteristics of pulsed lasers

Incorporating the vector feature of the laser field, the longitudinal spatial length, and the orientation distribution of the dipole moment in the gain medium, we develop a set of equations that describe the polarization dynamics of a class B laser with a modulated pump, a self-mode-locking laser, and an actively mode-locked laser with a modulated loss. Numerical results show that the first two types of laser operate in a linearly polarized state which changes direction while the third type of laser operates in an elliptical polarization state. In class B lasers with a modulated pump, because the coupling between the light and the medium depends on the dipole moment orientation of the population inversion, and the dominant gain appears alternately in different directions, the changing linear polarization state is induced by the cross-saturation effect of the two orthogonal linearly polarized laser fields. On the other hand, in the self-mode-locking laser the linear polarization state is the result of the coincidence of the dominant field polarization and gain preference for any of the two pulses within the cavity. For the actively mode-locked laser, the gain preference and the dominant polarization of the only pulse in the cavity are always perpendicular to each other, which makes the laser run in an elliptical polarization state.