Fourier transform deflectometry system and method

Abstract

The present invention relates to a Fourier transform deflectometry system () and method for the optical inspection of a phase and amplitude object () placed in an optical path between a grating () and an imaging system (), at a distance h of said grating. The grating () forms a contrast-based periodic pattern with spatial frequencies μ, vin, respectively, orthogonal axes x,y in an image plane, and the imaging system () comprises an objective () and an imaging sensor () comprising a plurality of photosensitive elements. Spatial frequencies μ, vare equal or lower than the Nyquist frequencies of the imaging system in the respective x and y axes. According to the method of the invention, a first image of said pattern, distorted by the phase and amplitude object (), is first captured through the objective () by the imaging sensor (). Then, a Fourier transform of said first image in a spatial frequency domain is calculated, at least one first- or higher-order spectrum of said Fourier transform is selected and shifted in said frequency domain, so as to substantially place it at a central frequency of said Fourier transform, and a reverse Fourier transform said at least one shifted first- or higher-order spectrum of said Fourier transform is performed so as to obtain a complex function g(x,y)=l(x,y)eiφ(x,y), wherein l(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θ, θin, respectively, the directions of the x and y axes, in the following form: φ(x,y)=−2ττh(μtan θ+vtan θy).