Low-frequency dynamics of a Nd-doped glass laser - art. no. 023816

We study a Nd-doped microchip glass laser that emits in two polarizations a nd in many longitudinal modes. Saturation of the inversion by standing wave s causes spatial inhomogeneity of both the longitudinal and azimuthal distr ibutions of the laser gain. These nonlinear inhomogeneities couple the mode s and result in low-frequency oscillations (10-500 kHz) of the light flux i n the individual laser modes. These oscillations are steadily driven by qua ntum noise and appear as 15% fluctuations of the power in each mode. In-pha se fluctuations in the laser modes appear at the frequency of the main rela xation oscillation of the total laser power. Antiphase fluctuations appear at other frequencies in individual longitudinal and polarization laser mode s only. The dominant frequency of these fluctuations is determined by the l ight power in the mode. Numerical simulations of rate equations, including Langevin forces, satisfactorily reproduce the experimental results. These p henomena must be taken into account when lasers are applied as stable coher ent optical light sources, and also with sensitive absorption measurements in the laser cavity.