Competition between two lasing modes of Sulforhodamine 640 in highly scattering media

Two lasing modes are observed for Sulforhodamine 640 in highly scattering media pumped by 3-ns 532-nm laser pulses. The stimulated-emission thresholds are found to depend on both concentration of laser dye and scattering particle density. At 2.5 x 10(-2) M dye solution with TiO(2) scattering nanoparticles from 5 x 10(9) cm(-3) to 10(11) cm(-3), the thresholds are found to decrease by more than 2 orders of magnitude. The dominating lasing modes are found to switch from 650 to 620 nm with the increase of density of scatterers.