Quantitative studies of evanescent wave intensity profiles using optical fluorescence

The fluorescence of uniformly distributed chromophores in an organic solution has been used to probe the energy density profile of an optical evanescent wave, generated by total internal reflection at the solid-solution interface. The results obtained in the case of an aqueous fluorescein solution in contact with a highly polished silica surface are in good quantitative agreement with the expected exponential decay of the optical energy at the interface. It also justifies the use of the newly developed evanescent wave-induced fluorescence technique to study adsorption and depletion layers of polymer in solution close to solids walls. In such experiments the fluorescence intensity is assumed to be the Laplace transform of the concentration profile of the fluorescently labeled polymer chains. The present data validate the above assumption.