Optical Phase Conjugation Enhanced by the Brillouin Interaction.

This thesis provides an in-depth study of the Brillouin interaction and how it can be exploited to enhance other nonlinear optical processes. The work begins with a detailed derivation of the equations of motion describing the stimulated Brillouin scattering (SBS) process. The derivation applies the principles of conservation of momentum and energy to a fluid particle in the medium, and evolves into a complete mathematical description of the SBS process including optical absorption and thermal effects. Predictions of the important parameters for this process, such as the SBS gain and reflectivity are given for the cases of a single and multimode laser. When using a multimode laser it is shown under what conditions the SBS gain and reflectivity are unaffected by the number of modes in the pump laser. Experiments carried out in this limit confirm the theoretical predictions. The novel scheme for combining SBS and conventional four-wave mixing into what is called Brillouin-enhanced four-wave mixing is discussed both theoretically and experimentally. This new geometry for producing a phase-conjugate signal is capable of combining the good feature of both the SBS and four-wave mixing processes, while eliminating the undesirable features of these processes. This Brillouin-enhanced four -wave mixing process produces a phase-conjugate mirror with reflectivities greater than 100%, with no frequency shift on reflection, and produces a high-fidelity phase-conjugate signal even when using aberrated pump waves. Experimental verification of all these features is demonstrated. A phase-conjugate oscillator consisting of a conventional mirror and a phase-conjugate mirror based on Brillouin -enhanced four-wave mixing has been constructed. The beam divergence and near-field spot size of this oscillator has been measured for various cavity lengths and radii of curvature of the conventional mirror. A theoretical analysis of the mode structure of this oscillator has been performed assuming a Gaussian reflectivity profile for the phase-conjugate mirror. The beam-parameter measurements made on the experimental phase-conjugate oscillators are in good agreement with our theoretical analysis.