Reflectivity of a spatially dispersive crystal

The reflectivity of a spatially dispersive crystal for s-polarized incident light at arbitrary incident angle is calculated for a microscopic model in which the interaction between crystal planes is assumed to fall off exponentially with distance (exp model). The case of normal incidence for this model has been previously considered by Sipe and Van Kranendonk and by Mead. The derivation is similar to that for normal incidence, the main difference being that the incident wave number is replaced by its normal component. The very simple derivation and result further illustrate the utility of the exp model. © 1978 The American Physical Society.