Thin film lasing from a dye-doped silica/titania composite

Thin-film gain media with rhodamine-doped silica(SiO2)/titania(TiO2) composite films were fabricated by the sol–gel technique. Laser action was observed from the optically pumped films by controlling the thickness and refractive indices of the SiO2/TiO2 matrices. The existence of a thickness cutoff for gain narrowing and light trapping in an optically richer film with a higher TiO2/SiO2 ratio suggested the contribution of multiple inward reflections of emitted light within simple asymmetric planar waveguides. Moreover, the peak separation between the observed discrete waveguided modes was strongly indicative of lasing with a longitudinal resonant structure.