Optical Properties of Dye Laser Thin Films Doped with Gold Nanoparticles.

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Laser action on thin films that operates without using an external cavity or constructing a periodic spatial structure is attracting interest for application to integrated photonic devices. In this study, we first fabricated thin gain media with rhodamine doped silica(SiOィイD22ィエD2)/titania(TiOィイD22ィエD2) composite films by the sol-gel technique. An existence of thickness cutoff for gain narrowing and light trapping in the optically richer film with higher TiOィイD22ィエD2/SiOィイD22ィエD2 ratio suggested a contribution of multiple inward reflections of emitted light within simple asymmetric planar waveguides. The observed peak separations between discrete waveguided modes were strongly indicative of lasing by a longitudinal resonant structure with coherent length in the order of tens of micrometers.Secondly, gold (Au) nanoparticles were fabricated in the SiOィイD22ィエD2/TiOィイD22ィエD2 films to modify their optical functions based on nonlinear optical effects and single electron charging phenomena. U … More nder ultraviolet irradiation, Au(III) ions doped in the films were reduced to generate gold particles accompanying an evolution of the surface plasmon band. Bu means of atomic force microscopy (AFM) using a conductive cantilever, local reduction of the Au(III) ions also generated Au particles embedded at a certain position of the film. The size of the particles were controlled by the voltages applied between the cantilever and an indium-tin-oxide coated glass substrate.Finally, fluorescence properties of rhodamine-doped SiOィイD22ィエD2/TiOィイD22ィエD2 films was controlled by incorporation of Au nanoparticles. As-deposited films doped with rhodamine and Au(III) ions exhibited no fluorescence due to quenching of the excited states of rhodamine by Au(III) ions. After generation of gold nanoparticles by photoreduction under ultraviolet irradiation, the rhodamine dye was reactivated to emit fluorescence. This photoresponsive phenomenon enabled us to make fluorescent micropatterns by selective particle generation in the film using a photomask as well as a UV pulse laser. Fabrication of fluorescence patterning was also carried out by local reduction of Au(III) ions using AFM with a conductive cantilever. Less