Superradiance in Experimentally Relevant Regimes

S. Haroche

J. C. MacGillivray, Michael S. Feld

This article reviews the present status of superradiance in atoms and molecules. The introductory section describes the important physical properties of superradiant emission, and presents the important experimental features. A simple theoretical formulation, based on the coupled Maxwell-Schrödinger equations, is described. Simple expressions for observable output parameters are given, valid in experimentally relevant regimes. These results are compared with superradiance experiments performed at a wide range of wavelengths in numerous laboratories since 1973. While the principal features of superradiance are generally agreed upon, details of the initiation of the radiation process and of the observed ringing are still under study.

L. I. Men’shikov

Stephan Asselie, A. Cipris, William Guerin

Super- and subradiance are usually described in the framework of Dicke collective states, which is an ``atomic picture'' in which the electromagnetic field only provides an effective interaction between the atoms. Here, we discuss a complementary picture, in which we describe the propagation and scattering of light in the atomic medium, which provides a complex susceptibility and scatterers. This ``optical picture'' is valid in the linear-optics regime for disordered samples and is mainly relevant at low density, when the susceptibility and scattering cross section can be computed from simple textbook formulas. In this picture, superradiance is a dispersion effect due to a single scattering event dressed by an effective refractive index, whereas subradiance is due to multiple scattering. We present numerical and experimental data supporting our interpretation.

Kyungwon An, James R Harries, Susumu Kuma

Ashat M. Basharov, N. V. Znamenskiı̆, A. Yu. Shashkov

Based on the analysis of the experimental data on the observation of the fluorescence and superradiance of praseodymium ions in a matrix of lanthanum trifluoride, a model of superradiance of three-level radiators with two close upper levels is developed in the mean-field approximation and studied. The uppermost level is coherently pumped by an ultrashort pulse of electromagnetic field, after which the excitation is transferred to the close energy level, from which the superradiance transition occurs to the lower level. In limiting cases, the considered model is reduced to the known models of superradiance and describes the ordinary regimes of monopulse and multipulse (oscillatory) superradiance. However, in a certain region of parameters, the model under discussion describes such a multipulse superradiance signal in which electromagnetic field spikes composing it follow in time with random intervals and amplitudes, so that the regime of regular chaotic dynamics is demonstrated in a single superradiance signal. In a certain time interval, the proposed model can be described by the Lorenz equations with the parameters corresponding to the chaotic dynamics of spikes composing the superradiance signal. The presented results of the numerical simulation of the model equations qualitatively correspond to the picture of stochastic pulsations observed experimentally.