Abstract
Using the formalism developed earlier, we treat spontaneous emission from a pair of identical two-level atoms , , whose separation can be comparable to the wavelength . We obtain expressions for time-dependent intensities and damping rates with the initial conditions (a) both atoms inverted, (b) prior excitation by a short pulse, and (c) only inverted. The results in (a) are compared with those obtained for a model consisting of two initially excited harmonic oscillators , . The atoms exhibit superradiant behavior, whereas , tend to trap radiation. In (a), the intensity pattern develops lobes in different directions at different times, so that the spatial distribution of photons at time is the same as in the independent-atom case . For the oscillators, the lobes of do not change direction, but only become more pronounced as time increases. In (b) and (c), the lobes oscillate back and forth at frequency corresponding to the shifts of the triplet and singlet states due to the interaction. The intensity can therefore have a sinusoidal component. Field correlation functions calculated for (a) and (c) show that and radiate simultaneously around the frequencies , where is the single-atom resonant frequency. The spectrum is calculated for case (c), and shows the effects of coherent linewidth enhancement in addition to the frequency shifts.
- Received 19 November 1969
DOI:https://doi.org/10.1103/PhysRevA.2.889
©1970 American Physical Society