# Polaritons in a spatially dispersive dielectric half space

## Abstract

An exact microscopic theory of volume and surface polaritons is developed for a spatially dispersive dielectric half space. No dielectric function is postulated; instead a collection of terms which is designated such arises naturally in the course of solving the microscopic equations that describe the response of the molecules to an external driving field. The excited states of the crystal are assumed to be Frenkel excitons which are treated in the tight-binding approximation. All intermolecular interactions are assumed to be of the point-dipole type. Formulas are derived for the reflection of s- and p-polarized light from the dielectric at arbitrary angle of incidence. Formulas are also given for the reflection of light inside a prism separated from the dielectric by a small gap as in attenuated-total-reflection experiments used to detect surface modes. Model calculations, using ZnSe parameters, exploring the effect of spatial dispersion on the optical properties are described. © 1976 The American Physical Society.