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Spontaneous emission of a two-level atom with an arbitrarily polarized electric dipole in front of a flat dielectric surface

We investigate spontaneous emission of a two-level atom with an arbitrarily polarized electric dipole in front of a flat dielectric surface. We treat the general case where the atomic dipole matrix element is a complex vector, that is, the atomic dipole can rotate with time in space. We calculate the rates of spontaneous emission into evanescent and radiation modes and study the angular densities of the rates in the space of wave vectors for the field modes. We show that, when the ellipticity of the atomic dipole is not zero, the angular density of the spontaneous emission rate of the atom may have different values for modes with opposite in-plane wave vectors. We find that this asymmetry of the angular density of the spontaneous emission rate under central inversion in the space of in-plane wave vectors is a result of spin-orbit coupling of light and occurs when the ellipticity vector of the atomic dipole polarization overlaps with the ellipticity vector of the field mode polarization. Due to the fast decay of the field in the evanescent modes, the difference between the rates of spontaneous emission into evanescent modes with opposite in-plane wave vectors decreases monotonically with increasing distance from the atom to the interface. Due to the oscillatory behavior of the interference between the emitted and reflected fields, the difference between the rates of spontaneous emission into radiation modes with opposite in-plane wave vectors oscillates with increasing distance from the atom to the interface. This difference can be positive or negative, depending on the atom-interface distance, and is zero for the zero distance.