Waveguide luminescence and Raman spectroscopy: characterization of an inhomogeneous film at different depths

In graded-index planar optical waveguides, different guided modes propagate in layers with different thickness. By comparison of spectra (Raman, luminescence) taken by waveguide excitation in different modes, it is possible to characterize the guide at different depths. The method has been applied to waveguides obtained by ion exchange of silver in a soda-lime substrate. Luminescence from silver ions and Raman scattering from the optical vibrations of the glass and from the acoustic vibrations of silver nanoclusters depend on the silver concentration, providing different spectra for excitation in different modes of the guide.