Influence of thiourea on the emission characteristics of a laser based on an aqueous solution of rhodamine 6G

An investigation was made of the spectral (luminescence and lasing) characteristics of an aqueous solution of rhodamine 6G with an addition of thiourea. When the thiourea concentration in the solvent was $\gtrsim$ 30 %, the absorption and fluorescence spectra changed greatly, the lasing threshold decreased approximately fourfold, and the output power increased by an order of magnitude. The good thermooptical properties of water as a solvent, in combination with the disaggregation properties of thiourea, made it possible to realize (without circulation of the solution) a pulse-periodic lasing regime at a repetition frequency of $\lesssim$ 50 Hz and with output radiation parameters typical of a laser with continuous circulation of an ethanol solution of rhodamine 6G.