Fabrication and Characterization of Uranium Oxide Doped Sol-Gel Planar Waveguides for Attenuated Total Reflectance Spectrometry

Planar integrated optical waveguides doped with fluorescent hexavalent UO₂²⁺ ions were fabricated by a sol-gel dip-coating process. Excitation of a mode in these waveguides produced fluorescence emission that decayed in a highly uniform manner as a function of propagation distance. A comparison of methods for determining waveguide attenuation coefficients by digital photography of the mode demonstrated that imaging the UO₂²⁺ fluorescence emission is significantly more precise than imaging the Rayleigh and Mie scattered light. The utility of these waveguides for performing attenuated total reflectance measurements on substrate-supported molecular films was also assessed. Both the fluorescence and scattering methods were used to determine the attenuation coefficient of an adsorbed heme protein monolayer. The fluorescence imaging method was clearly superior; its use enables attenuation measurements of very weakly absorbing, waveguide-supported films to be performed with significantly improved precision.