Quantum electrodynamics of an atom in front of a non-dispersive dielectrichalf-space

The energy-level shifts and the change in the rate of spontaneous emission are calculated for an atom located at a distance Z from a dielectric half-s pace. The dielectric is a non-dispersive and non-absorbing medium character ized by a constant real refractive index n. The explicit analytic formulae derived are applicable for arbitrary values of n. All results are analysed in the non-retarded and retarded limits, which apply to the atom being clos e to or far from the interface. respectively, i.e. to Z being small or larg e on the scale of a wavelength of a typical atomic transition. For ground-s tate atoms, the energy-level shift varies as 1/Z(3) in the non-retarded reg ime and as 1/Z(4) in the retarded regime, which agrees with the Casimis-Pol der result for the limit n. --> infinity. For excited-state atoms, the ener gy-level shifts receive additional contributions that oscillate with the di stance Z from the interface.