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Le Journal de Physique Colloques

INSTABILITIES IN THERMAL BATH : PHONON ENHANCEMENT AND SATURATION IN A THREE-LEVEL SYSTEM

Benjamin Fain

Published Dec 1, 1981• 0 citations
Publisher

Abstract

The equations, determining temporal behavior of coupled electronic and phonon subsystems in the electromagnetic field, are analyzed. The steady state solution describing saturation of the three level in such a system is achieved. It is shown that laser-like self-excitation of phonons cannot be obtained though essential phonon enhancement may be gained provided certain conditions are fulfilled. Field induced transparency is predicted between first two levels when the field saturates ground and highest levels, and the concentration of ions is high.

DOI
10.1051/jphyscol:19816158

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The equations, determining temporal behavior of coupled electronic and phonon subsystems in the electromagnetic field, are analyzed. The steady state solution describing saturation of the three level in such a system is achieved. It is shown that laser-like self-excitation of phonons cannot be obtained though essential phonon enhancement may be gained provided certain conditions are fulfilled. Field induced transparency is predicted between first two levels when the field saturates ground and highest levels, and the concentration of ions is high.
A model consisting of a distribution of three-level systems (defects or ionic impurities) in a lattice characterized by a given phonon spectrum is considered in detail. Equations determining the temporal behavior of such a system in an electromagnetic field are analyzed. A steady-state solution describing three-level saturation in the system is achieved. The possibility of the stimulated emission of phonons is considered. It is shown that laserlike self-excitation of phonons cannot be realized, though phonon flux enhancement may be achieved provided certain conditions are fulfilled.
The theory of relaxation processes is reviewed starting from first principles. The resulting equations of motion describing the temporal behavior of two subsystems---dynamic and dissipative---are discussed. In existing theories the dissipative system or a thermal bath is assumed to be in thermal equilibrium all the time. The basic aim of this paper is a derivation of the instability conditions of the thermal bath. For this purpose two specific models are examined. One is an ensemble of inhomogeneously broadened two-level systems coupled with harmonic excitations (phonons) and the other is the ensemble of homogeneously broadened two-level systems interacting with a phonon bath. Possible implications, including biological ones, of the derived instability conditions are mentioned.
An inhomogeneously broadened three-level electronic system related to impurity ions embedded in a crystal with anisotropic phonon modes is considered. It is shown that such a system can sustain laserlike self-excitation under a steady-state condition, depending on the crystal properties. The anisotropy of the phonons is represented by two sets of modes which are distinguished by their lifetimes. Laserlike self-excitation has been shown to be impossible for isotropic systems. This and the influence of crystal properties on the self-excitation in anisotropic systems are discussed.