Competition and Coexistence of Raman and Random Lasing in Silica-/Titania-Based Solid Foams

Recently, competing random lasing and stimulated Raman scattering mechanisms have been observed for the same gain medium infiltrated in diffusive silica-based solid foams. Specifically, the light transport mean free path ℓt in such disordered media has been identified to be a parameter of choice to tune the observation of either Raman or random lasing. In this contribution, novel silica-/titania-based solid foams are designed that allow tuning this ℓt parameter significantly, by one order of magnitude. This being achieved, the transition from "pure" random to "pure" Raman lasing is shown, while going through a state of concomitant existence of both mechanisms. The experimental results are well understood, owing to simulations of a simple 1D diffusive model, which suggests that both gain mechanisms may present a complex interplay, leading to random Raman lasing. Novel silica-/titania-based solid foams for increasing fractions of titania allow tuning of the disorder strength of these 3D disordered white materials.