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

TLDR

Laser action of Rhodamine 640 perchlorate in TiO₂‑nanoparticle methanol, pumped by 3‑ns 532‑nm pulses, was detected via spectral and temporal measurements. The stimulated‑emission threshold decreases with increasing dye and scattering‑particle concentrations, dropping over two orders of magnitude at 2.5×10⁻² M dye when particle density rises from 5×10⁹ to 2.5×10¹² cm⁻³, but rises at 5×10⁻⁴ M dye, while the emission pulse lasts ~50 ps.

Abstract

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.