Nonlinear refraction measurements of materials using the moire deflectometry

In this study, a new method for measuring the nonlinear refractive index of materials using the moire deflectometry is reported. We describe the experimental details and present theoretical analysis for obtaining the magnitude and the sign of nonlinear refractive index of materials, n(2),, using the moire fringe patterns. Optical-field induced refractive index changes in materials leads to well-known self-focusing/defocusing effects (self-lensing effect). In presence of a sample of nonlinear refractive material, the convergence or divergence of a collimated incident laser beam is monitored by the moire deflectometry system. The results show that the moire fringes rotate about the beam center and the fringes sizes change too because of the induced self-lensing effects in the sample. The nonlinear refractive index of materials and its sign is obtained by analyzing the moire fringes patterns. The theoretical aspects of the method are presented and the relationship between the moire fringes rotation and the nonlinear refractive index is derived. Our method is applied for measuring the nonlinear refractive index of Fe2O3 nanoparticles in toluene solution under 5-mW He-Ne laser (lambda = 632.8 nm) illumination. The value of n(2) = -4.9 x 10(-7) cm(2) W-1 is obtained for Fe2O3 nanoparticles in toluene solution and it is in excellent agreement with the reported value in literature. (C) 2004 Elsevier B.V. All rights reserved.