Light Scattering by a Phase Conjugator in the Four-wave Mixing Configuration

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Abstract
Reflection of travelling and evanescent plane waves by a four-wave mixing phase-conjugator is studied in detail. No restrictions are imposed on the nonlinear interaction strength, the angle of incidence or the frequency mismatch between the pump-beams and the incoming waves. We only assume that the incident field is weak compared to the pump fields, which justifies a classical field description of the pumps. The wave-vectors, amplitudes and phases for the various waves are evaluated, without the slowly-varying amplitude approximation. Familiar phase-matching resonances for certain values of the interaction length are recovered, and in addition strong resonances are found if the angle of incidence is finite and the incident light is not in perfect resonance with the pumps. The latter resonances appear at the transitions from a travelling to an evanescent wave. The significance of finite angles of incidence and evanescent waves for spectroscopic applications is pointed out.