Comment on Nonlinear refraction measurements of materials using the moire deflectometry

In an influential paper Jamshidi-Ghaleh and Mansour [1] (Opt. Commun. 234 (2004) 419), have reported on a new method for measuring the nonlinear refractive index of materials using the rotational moire deflectometry technique. In the cited work, the authors apply the ray matrix theory for Finding the beam deflection angle on the plane of the first grating in the used geometry. To this end, using the parabolic approximation, the exponential term in the beam irradiance is expanded and retaining the first two resultant terms, the nonlinear sample is treated as a thin lens with a position dependent focal length. In this comment, the effective focal length of the nonlinear sample has been redeiived in detail using the Gaussian beam theory and it is shown that it must contain a correction factor. The relative error introduced by ignoring this factor can be as large as 735-844% in determining the nonlinear refractive index of thin samples. (C) 2014 Elsevier B.V. All rights reserved.