Effect of the solvent viscosity on the local irregular intensity fluctuations in high Fresnel number dye lasers

We study the influence of the solvent viscosity in the local irregular inte nsity fluctuations characteristic of high Fresnel number dye lasers, The re lative amplitude of the fluctuations in a flashlamp-pumped dye laser is ana lyzed,We complete our previous work by using several solvents and different excitation energies above threshold. A decrease of the relative fluctuatio n amplitude is found as the solvent viscosity or the pumping energy increas es, This effect is theoretically analyzed in the framework of the semiclass ical Maxwell-Bloch equations, with a model based on the orientation of the dye molecules driven by the laser field in the solvent. These results point out the importance of the orientation of the dye molecules in the intensit y fluctuation phenomenon.