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In this paper, a visual rapid technique is presented for the sign identification of nonlinear refractive index of colloidal nanoparticles based on non-scanning Moire deflectometry technique. In this method two lasers are used, one as a pump laser beam which causes thermal nonlinear effects in the sample and the second one is used as a probe beam laser which allows us to monitor these effects by Moire deflectometry technique. The gradient of the nonlinear refractive index produced by the interaction of the pump laser, generates a cylindrical lens in the sample. The concave and convex lenses are produced as a result of negative and positive nonlinear refractive index respectively. Geometrical and experimental investigations show the Moire fringes are deflected in two different directions by these lenses. By observing the shape of deflected moire fringes, we can determine the sign of nonlinear refractive index and there will be no need for calibration or complicated calculations. This technique was applied for identification of nonlinear refractive index of Au and Tio_2 colloidal nanoparticles, under 47 mW second harmonic of Nd:YAG laser illumination. The sign of nonlinear refractive index of colloidal Au and Tio_2 nanoparticles were observed to be negative and positive respectively.

Sign Identification of Nonlinear Refractive Index of Colloidal Nanoparticles by Moiré