Absorption Optics of Aqueous Foams

The absorption of photons by aqueous foams is studied using diffuse transmission spectroscopy (DTS). The liquid phase of the foam is made absorbing by adding rhodamine dye to the surfactant solution. It is found that for a range of foam liquid volume fractions, the absorption lengths calculated from DTS experiments are smaller than the estimates given by the respective volumes of the two phases. We conclude that multiply scattered photons can get channeled into the liquid network. Computer simulations also show this phenomenon. Our results encourage us to consider novel mechanisms of transport of photons, such as their total internal reflection inside the Plateau borders.