Quantum electrodynamics near an interface

A quantum-mechanical linear-response formalism is used to calculate the frequency shift and lifetime of an excited atom near an arbitrary flat interface. The results depend on the frequency-dependent atom and field susceptibilities, and in the vicinity of an interface can be expressed in terms of the appropriate Fresnel reflection coefficients; the contributions from surface excitations are easily identified. As examples, we consider an atom above a metal and a dielectric waveguide.