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A cavity-like regime of superradiance for a double-layer medium populated by atoms with the A-scheme of transitions is considered in a semiclassical approximation under the condition that the layers are arranged symmetrically with respect to initial characteristics of the field and atomic system populating the layers. An analytical law for the linear stage of the superradiance process is found that agrees well with numerical solution of the differential equations of the model under consideration for any initial conditions nearly up to the peak of the appropriate characteristic of the field intensity module. For the case of degenerate lower doublet, the resonant character of the dependence of the superradiance pulse time delay on the distance between the layers is studied. [ABSTRACT FROM AUTHOR]

Excitation of stimulated photon echo by two incoherent pulses obtained from one source and one coherent pulse is considered. The dependence of the average amplitude of stimulated echo on the parameters of noise pulses is determined. The results can be used for analysis of the corresponding algorithm of excitation of stimulated spin echo, as well as in calculations of characteristics of the signal processors based on the phenomena of photon and spin echoes. [ABSTRACT FROM AUTHOR]

The effect of the sample extent in the process of superradiance and superradiance without population inversion of a thin (L ≤ λ) layer of three-level atoms (Λ-configuration of working transitions) is investigated. The limits of applicability of the spatially homogeneous approximation are determined. The consideration of the extent is shown to introduce new effects into the kinetics of populations and the field. [ABSTRACT FROM AUTHOR]

The effect of a local field on the transition competition in the process of superradiance of a thin layer of three-level atoms (Γ-configuration of working transitions) in the presence of an initial coherence of the lower doublet is investigated. It is shown that under the action of a local field, a coherent Raman transition between sublevels of the lower doublet can take place. [ABSTRACT FROM AUTHOR]

We analyze the possibility of superradiance in an ensemble of three-level atoms in the absence of population inversion. We show that in the case of a A configuration of the active transitions this effect can occur for an initially coherent superposition of the states of the lower doublet. We also study how splitting of the lower levels influences this effect and discuss ways of creating low-frequency coherence. [ABSTRACT FROM AUTHOR]