Relaxation in Macroscopic System: An Information Theoretic Approach

Abstract

There are essentially two reasons why a simple yet quantitative approach to relaxation of a system in disequilibrium is relevant to laser research and applications. The direct and obvious one is that the operation of any atomic or molecular laser is dependent on maintaining the active medium in a state of disequilibrium (‘population inversion’). Non-radiative relaxation processes drive the system towards equilibrium and thus tend to reduce the efficiency. A realistic modelling of the laser must allow for such loss processes. In addition however, lasers offer a particularly concenient way of selectivity driving a system away from equilibrium. This selective excitation offers many potential applications (1–3). Here again, the relaxation processes tend to diminish the selectivity of the initial excitation, degrading it ultimately into heat. As a concrete example we shall consider vibrational relaxation (4, 5). Diatomic molecules, in an excess of buffer gas are displaced from vibrational equilibrium (See, e.g. (6)). Collisional (vibration-to-translation) energy transfer will then act to restore equilibrium.

Work supported by the Stiftung Volkswagenwerk.