Observation of stimulated emission from Rhodamine 6G-polymer aggregate adsorbed at foam interfaces

This paper reports for the first time the observation of stimulated emissions from the gas-liquid interface between two adjacent bubbles in highly ordered foams containing Rhodamine 6G and surfactant. Stimulated emissions centred at 595 nm were observed when a monolayer of foam (~liquid fraction 0.11), placed on a highly reflective surface, was subjected to a 532 nm continuous wave laser directed along ~45° from the direction perpendicular to the substrate. Additionally, using confocal microscopy and micro-photoluminescence, it was found that the liquid fraction of the foam, the gap between two adjacent bubbles and the incidence angle of the laser are important parameters in guiding the light and promoting stimulated emissions at the interface. The adsorption of the polymer and dye increased the local concentration at the narrowest gaps between pairs of bubbles, which led to the formation of hemispherical micelles-dye agglomerates. The presence of the micelles aggregation caused random scattering induced stimulated emission. These results could have a significant impact on a number of applications, such as photocatalytic conversion at bubble interfaces, where TiO2 can scatter light and hence reaction rates may be increased.