Spontaneous pulsations in gas class-A lasers with weakly anisotropic cavities

Abstract

Spontaneous pulsations and polarization multistability resulting from the nonlinear interaction of two standing waves with an active medium in a single-longitudinal-mode Fabry-P\'erot gas laser with a weakly anisotropic cavity have been studied at different cavity anisotropies and different transitions between the working levels with and without an axial magnetic field applied to the active medium. As predicted theoretically, a series of polarization dynamical phenomena have been observed experimentally in the He-Ne $(\ensuremath{\lambda}=1.15\ensuremath{\mu}$m) laser in the case of orthogonal elliptically polarized eigenstates of the cavity. Periodic oscillations of two qualitatively different forms (distorted sinusoids and large spikes), the transition between two stationary orthogonal elliptically polarized waves in the vicinity of the line center tuning which occurs through the region with polarization instability, as well as switches between the orthogonally polarized components when the output is nonstationary have been found. It is shown that the diversity of nonstationary polarization phenomena in gas lasers with weakly anisotropic cavities is due to spontaneous pulsations of intensities, ellipticities, and azimuths of two emitted waves, caused by the competition of the nonlinear active medium and empty cavity anisotropies. The results of the theoretical modeling are in quantitative agreement with the experimental results.