Nonlinear Interactions of Electromagnetic Waves in an Active Medium and Their Possible Application to the Development of New Types of Lasers

Abstract

Advances in laser technique now enable the production of light fields with a strength of 10⁶-10⁸ V/cm. In such fields the medium becomes nonlinear, i.e., the principle of superposition breaks down: Different waves interact with one another as they propagate; for instance, the propagation of waves of one frequency gives rise to waves of other frequencies, and so on. In quantum language such effects are described by multiphoton processes. Multiphoton processes are interactions of radiation with matter in which at least two photons are absorbed or emitted in each elementary act; the probability of such an act differs considerably from the product of the probabilities of individual one-photon processes. It should be noted that some multiphoton effects, such as Raman scattering, resonance fluorescence, etc., had been observed even before lasers were produced. Multiquantum processes were investigated theoretically in the early years of quantum mechanics; for instance, two-photon emission and absorption were examined as long ago as 1931 [1].