Laser action of Rhodamine 640 perchlorate in highly scattering media consisting of TiO2 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 × 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 × 109 to 2.5 × 1012 cm-3. However, for a concentration of 5 × 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.
© 1994 Optical Society of America
W. L. Sha, C.-H. Liu, and R. R. Alfano, "Spectral and temporal measurements of laser action of Rhodamine 640 dye in strongly scattering media," Opt. Lett. 19, 1922-1924 (1994)