DYNAMICS OF A CW MULTIMODE DYE-LASER

The spectral and temporal dynamics of a multimode dye laser has been s tudied theoretically and experimentally. The analytical model includes quantum fluctuations as well as four-wave mixing due to population pu lsations, stimulated Brillouin scattering, and Rayleigh scattering bot h in a standing-wave linear laser, and in a unidirectional ring laser. The nonlinearity found most important in the multimode dye laser is f our-wave mixing due to pulsations of the population of the upper laser level. Numerical simulations show features that characterize this par ticular type of mode coupling: broadening of the emission spectrum, os cillations of the light flux in individual laser modes, suppression of certain beat notes. Observations of these features confirm population pulsations dominating the laser dynamics. Four-wave mixing due to pop ulation pulsations tends to arrange the phases of the laser modes such as to minimize the pulsations and to limit its own strength.