Spectral and temporal measurements of laser action of Rhodamine 640 dye in strongly scattering media.

Laser action of Rhodamine 640 perchlorate in highly scattering media consisting of TiO(2) nanoparticles in methanol pumped by a 3-ns 532-nm laser pulse is observed by use of spectral and temporal measurements. The threshold for stimulated emission is dependent on the concentration of both laser dye and scattering particles. For a 2.5 x 10(-2) M dye concentration, the lasing threshold was found to be reduced by more than 2 orders of magnitude when the density of scattering particles was increased from 5 x 10(9) to 2.5 x 10(12) cm(-3). However, for a concentration of 5 x 10(-4) M of Rhodamine 640 the lasing threshold was higher in scattering media than for the methanol host. The pulse duration of stimulated emission for Rhodamine 640 perchlorate in these random systems is ~50 ps.