Boundary Conditions in Case of Spatial Resonance Dispersion

Abstract
A simple model accounting for the influence of a surface on polariton waves is introduced. From this the extra boundary condition needed in case of a dispersive resonance is derived. The general result is discussed in relation to actual resonances in crystals. The theory of bulk waves and their boundary conditions is extended to include two or more dispersive resonances. The behavior of the measured exciton lines in ZnO agrees well with the computed spectra.