Supported sol-gel thin-film glasses embodying laser dyes II: three-layered waveguide assemblies

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Abstract
Three-layered thin-film assemblies of polymethysiloxane (PMSO) glass were prepared by fast reaction of methyltrimethoxysilane with water, using stoichiometric water-to-siloxane ratios, at elevated temperatures. Following hydrolysis, partial polymerization and distilling-out of the produced methanol, the viscous polymer of each layer was spin-cast onto the support. The layered assemblies comprised a bottom and top layers made of pure PMSO, and a middle layer embodying the laser-dye. A specific tuning of the synthetic route was maintained to ensure proper adherence between the layers, since PMSO surface rearranges itself to become hydrophilic or hydrophobic, depending on the environment it is facing. An additional tuning facilitated molecular dispersion of dye in the glass, even at high concentrations (>10-2 M). The absorbance and fluorescence spectra of the thus-embodied dyes showed typical features, while their absorbance - fluorescence gap was substantially narrowed. The indices of refraction in the three-layered assemblies were lower in the base and top layers, and a little higher in the dye-loaded middle layer. Fluorescence line-narrowing of the emission from the glass-edge could be observed upon excitation of the dye surface with an excimer laser at 308 nm. This lasing of the sol-gel glass- film was characterized by line width narrowing by 25-40% and an angular width of ca. 6 deg. The quickness and simplicity of preparing multilayered assemblies of varying indices of refraction by this method and its capability to maintain high concentrations of discrete dye molecules (>10-2 M) in the middle glass-layer offer a promising route for two-dimensional laser systems and for non-linear optics applications in general.

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