Absolute and convective superradiance: Dynamics and macroscopic quantum fluctuations

Classical and quantum dynamics of superradiance in macroscopic samples of active media is discussed. Along with the usual convective instability, the absolute instability is analyzed as the basis of the superradiance phenomenon. Various regimes of superradiance in a conducting inverted two-level medium immersed in the plasma under and out of the condition of plasma-dipole resonance are described and compared. It is shown that the absolute instability of long-wavelength high-frequency polarization waves results in the pulsed generation of strong nonradiating electric fields. The remarkable phenomenon of macroscopic manifestation of quantum fluctuations in the observable parameters of superradiance is described. A general method of the quantization of unstable normal modes in the systems of coupled partial modes with opposite-sign energies is developed. Delay-time statistics of the superradiance pulse is examined in detail. New experiments for the observation of the outlined effects in the nonequilibrium activated semiconductors and partially ionized gases, e.g., in impulsive discharge, in the infrared range are proposed and appropriate estimates are provided.