Table of contents

The current theory of superradiance is described. The effect is due to interatomic correlations (phase-locking) which arise under the action of a general electromagnetic field and are determined by the competition between the electron motion anharmonicity and the interatomic dipole–dipole interaction. The latter affects significantly the nature of the superradiance effect. A common nature for the radiations from a Dicke atomic ensemble and from collective waves in a substance (for example, cyclotron waves in a magnetized plasma) is established. Superradiance manifests itself in hot magnetically confined plasmas and accounts, among other things, for anomalous heat conductivity in tokamaks.

Statistical models of an electron solvated in a classical liquid are reviewed. The analogy between the behaviour of a quantum particle and a polymer chain results in that statistical physics methods can be applied to the solvated electron problem. We have derived basic relations for thermodynamic and structural characteristics of the solvated electron. The free energy of the solvated electron and the effective electron–solvent potential as well as the electron–solvent correlation function are studied in detail. The calculated results are compared with experimental data and a quantum molecular dynamics simulation for simple, polar, and Coulomb liquids. We also outline many-particle quantum effects, such as electron–electron interactions and dielectron (bipolaron) formation. The potentialities and restrictions of the statistical method are also discussed.

Basic ideas of the statistical topography of random processes and fields are presented, which are used in the analysis of coherent phenomena in simple dynamical systems. Such phenomena take place with probability one, and provide links between individual realizations and statistical characteristics of systems at large. We confine ourselves to several examples: transfer phenomena in singular dynamic systems under the action of random forces; dynamic localization of plane waves in randomly stratified media; clustering of randomly advected passive tracers; and formation of caustic structures for wave fields in randomly inhomogeneous media. All these phenomena are studied based on the analysis of one-point (space-time) probability distribution functions.

Evidence for persistent photoconductivity, i.e., electrical conductivity changes existing for a very long time after the excitation of nonmetallic solids by photons, was furnished back in the 19th century and put to practice even before modern solid-state physics had developed. At present, two complementary models are basically used to explain this phenomenon. One involves the trapping of nonequilibrium charge carriers by point centres of localization (traps) which slows down the recombination of electrons and holes generated by light or charged particles. In the other, electrons and holes are also separated spatially and prevented by potential barriers from recombination. Both types of relaxation process are discussed and experimental data, with special emphasis on the charge separation idea, presented.

The possibility of the brightness and temperature of scattered radiation exceeding the attendant magnitudes for the incident radiation is predicted for the case of a noninverted medium, based on the analysis of radiation transfer equations. The irreversible nature of the process and impossibility of introducing ray approximation are identified as the necessary conditions.