New physical explanation of phase-conjugate waves produced in backward stimulated scattering

N. F. Pilipetskiy, V. I. Popovichev, V.V. Ragulskiy

J.L. Ferrier, Zhiqiang Wu, José Gazengel +2 more

Four-wave mixing and stimulated backward scattering1,2 allow the production of phase conjugate signals.

Dun Liu, Guang S. He

A quasi-collinear and partially degenerate four-wave mixing model is proposed to explain the optical phase-conjugation property of various types of stimulated backscattering. According to this model, after passing through a phase-disturbed medium or an aberration plate, the input pump beam can be resolved into two portions: a stronger undisturbed regular portion and a weaker phase-disturbed irregular portion. These two portions interfere with each other and create a volume holographic grating in the pumped region of the scattering medium. Only the stronger undisturbed portion of the pump field can excite an initial backward stimulated scattering beam with a regular wavefront. When the latter (as a reading beam) passes through the induced holographic grating, a diffracted wave will be created and then amplified together with the reading beam. A rigorous mathematical analysis shows that under certain conditions the combination of these two portions (the reading wave and the diffracted wave) of the backward stimulated scattering can be an approximate phase-conjugate field of the input pump field. The major theoretical conclusions are basically supported by the experimental results based on a specially designed two-beam interference setup.

Boris Ya Zel'dovich, N. F. Pilipetskiǐ, Vladimir V. Shkunov

Guang S. He

Optical phase conjugation (OPC) is a nonlinear optical technique for the generation of phase conjugate waves (PCWs) and their application. For a coherent and monochromatic light wave (signal beam) with a given wavefront shape, one can generate a new light wave with a reversed wavefront shape (with respect to the propagation direction) via nonlinear optical methods. This newly generated optical wave is termed the PCW of the input signal beam. Three major nonlinear optical methods can be employed to generate various PCWs: nonlinear four- or three-wave mixing, backward stimulated scattering, and backward stimulated emission (lasing). PCWs can overcome disturbing and aberration influences from the propagation medium. Therefore, this technique is especially useful in high brightness laser oscillator/amplifier systems, laser aiming and targeting systems, and long-distance and high bit-rate optical fiber communication systems. It also provides an effective approach to achieve lasing or stimulated scattering from a randomly disturbed gain medium.

Alexander M. Lazaruk