Electrodynamics of nonlocal media

A method, based upon Wiener-Hopf techniques, is presented for calculating the reflectivity of an s- or p- polarized plane electromagnetic wave from a semi-infinite medium whose dielectric response is spatially nonlocal. The method is applicable to media that can be adequately described by the dielectric approximation and by two scalar dielectric response functions, εL(→r, ω) and εT(→r, ω), which are subject only to weak boundedness and asymptotic conditions. As an example of the method, the reflectivities are calculated for a medium characterized by a dielectric response appropriate to the neighborhood of an isolated exciton transition frequency.