Microscopic Theory of Correlation Induced Shifts of Spectral Lines
Wolf has discovered that the spectrum of the radiation emitted by a source depends critically on the spatial coherence characteristics of the source. He has constructed phenomenological models to demonstrate how the spatial coherence can lead to blue or red shifts of the spectral lines or even produce several lines instead of one line. Several laboratory experiments have confirmed Wolf’s predictions. We have been examining the microscopic models for the shifts which arise from the spatial coherence characteristics of the source. A simplest model will involve two radiating atoms in the close vicinity of each other. The dipole-dipole interaction between the atoms leads to spatial correlation and hence the spectral shifts. We use a fully quantized field approach to demonstrate the existence of red and blue shifts in terms of this model. We further show how the dipole-dipole interaction can lead to a two photon resonance in the spectra. Another example of a similar effect is the shift in the frequency of an atom radiating in presence of a dielectric or metallic mirror. Finally the relation of correlation induced shifts to the other types of shifts such as Lorentz shifts and the shifts in absorption say by a system of distributed particles in a host material will be described.