P-scan analysis of inhomogeneously induced optical nonlinearities

A model for beam propagation through a nonlinear material is developed; the model takes into account inhomogeneous induced refractive-index changes due to the nonlinearity. A focused Gaussian beam of circular cross section, incident upon the sample, emerges as an elliptic Gaussian beam after interaction in this material. The nonlinearity coefficient values derived from a Z scan of photorefractive lithium niobate crystals compare favorably with that found by varying the power P of a Gaussian beam focused at a fixed longitudinal position within the sample and monitoring the far-field beam ellipticity. The nonlinearity coefficient value is used to determine the dopant’s acceptor-to-donor concentration ratio in photorefractive lithium niobate samples.

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