Quantum Theory of Interaction of Radiation Field with Matter

Krishnan Thyagarajan, Ajoy Kumar Ghatak

Ajoy Kumar Ghatak, S. Lokanathan

Victor Nikolaevich Popov, Vladimir Sergeevich Yarunin

William Hughes Miller

A classical model for the interaction of molecular systems with infrared radiation is presented. It differs from the usual ’’semiclassical theory of radiation and matter’’ in that the molecular system is treated by classical rather than quantum mechanics, and the radiation field is described, as in Jaynes’ neoclassical theory, as classical (mechanical) harmonic oscillators rather than as a classical field (i.e., via Maxwell’s equations). The classical Hamiltonian for the composite system—molecules, radiation, and their interaction—is thus that of a completely mechanical system, and its classical dynamics is determined by computing the classical trajectories of the system. Quantum mechanical interference and tunneling effects can be built into the description within the framework of the classical S-matrix theory. Even within the strictly classical limit of the model, it is shown that all dynamical effects in the interaction of radiation and matter are obtained; in the perturbative limit, for example, it is shown that absorption and induced emission, and even spontaneous emission, which is often difficult to obtain in other classical or semiclassical models, appear in a completely straightforward manner.

Weihan Tan, Weiping Lu, Robert G. Harrison

We report an alternative approach to describe radiation-matter interaction that extends conventional perturbation theory to accommodate arbitrary field strength by introducing the concept of self-regulated partitioning of the interaction Hamiltonian. The treatment gives a clear physical insight into field-induced splitting of the states, called here partially dressed states, and also accounts for the transition of energy between the states. In general these states are characterized by the strength and form of the field-matter interaction and determined by comparison with density-matrix analysis. Using these states as base states, this theory allows for a perturbation-expansion analysis for arbitrary interaction strength. This treatment provides an analytic basis for describing multilevel radiation interactions, and by way of example we consider its application to third-harmonic generation.