Considering that the nonlinear photoinduced phase shift to a Gaussian beam in a thin sample of nonlocal nonlinear media can be modeled as a Gaussian function to some real power the far-field can be calculated using the Fraunhofer integral. In this paper we calculate numerically this integral to obtain the on-axis intensity in a Z -scan experiment or the intensity pattern in a self-phase modulation experiment. Experimental results of samples under cw illumination are fitted using the model with a good correspondence between experimental and numerical results. The model presented is adequate to describe samples with any magnitude of the maximum nonlinear photoinduced phase shift of purely refractive local or nonlocal nonlinear thin media.

Analytical expressions for the normalized transmittance of a thin material with simultaneous nonlocal nonlinear change in refraction and absorption are reported. Gaussian decomposition method was used to obtain the formulas that are adequate for any magnitude of the nonlinear changes. Particular cases of no locality are compared with the local case. Experimental results are reproduced (fitted) with the founded expressions.

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In this paper the response purely refractive of a thin nonlinear material, in the z-scan technique experiment, is modeled as a lens with a focal length that is a function of some integer power of the incident beam radius. We demonstrate that different functional dependences of the photoinduced lens of a thin nonlinear material give typical z-scan curves with special features. The analysis is based on the propagation of Gaussian beams in the approximation of thin lens and small distortion for the nonlinear sample. We obtain that the position of the peak and valley, the transmittance near the focus and the transmittance far from the Rayleigh range depend on the functional dependence of the focal length. Special values of the power reproduce the results obtained for some materials under cw excitation.

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