Gaussian decomposition method was used to obtain the formulas that are adequate for any magnitude of the nonlinear changes. Considering that the nonlinear photoinduced chapter shift to a Gaussian beam all the rage a thin sample of nonlocal nonlinear media can be modeled as a Gaussian function to some real ability the far-field can be calculated using the Fraunhofer integral. Their third order nonlinear response was studied using the z-scan technique at nm with 26ps pulses. In this work we present a simple model to calculate, all the rage a numerical way, the on axis far field intensity in a Z-scan experiment or the far field pattern in spatial self phase modulation experiment by means of the diffraction theory and taking into account the locality of the thin nonlinear media. The results showed the influence of Au deposition in the PL response.