US 8,422,822 B2 · Fourier transform deflectometry system and method

Abstract

The present invention relates to a Fourier transform deflectometry system (1) and method for the optical inspection of a phase and amplitude object (2) placed in an optical path between a grating (3) and an imaging system (4), at a distance h of said grating 3. The grating (3) forms a contrast-based periodic pattern with spatial frequencies μ0, v0 in, respectively, orthogonal axes x,y in an image plane, and the imaging system (4) comprises an objective (5) and an imaging sensor (6) comprising a plurality of photosensitive elements. Spatial frequencies μ0, v0 are 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 (2), is first captured through the objective (5) by the imaging sensor (6). 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 θx, θy in, respectively, the directions of the x and y axes, in the following form: φ(x,y)=−2ττh(μ0 tan θx+v0 tan θy).

Claims22

Dependent claims

A deflectometry method for the optical inspection of a phase and amplitude object placed in an optical path between a single grating and an imaging system, at a distance h of the grating, wherein the grating forms a contrast-based periodic pattern with the spatial frequencies μ0, v0 in, 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, wherein this method comprises the step of:

capturing through the objective, with the imaging sensor, a first image of said pattern distorted by the phase and amplitude object;
and is characterised in that said spatial frequencies μ0, v0 are not higher than the respective Nyquist frequencies of the imaging system on said axes x,y, and this method also comprises the steps of:
calculating a Fourier transform of said first image in a spatial frequency domain;
selecting at least one first— or higher-order spectrum of said Fourier transform and shifting it in said frequency domain so as to substantially place it at a central frequency of said Fourier transform;
and
carrying out a reverse Fourier transform of said at least one shifted first- or higher-order spectrum of said Fourier transform so as to obtain a complex function g(x,y)=I(x,y)eiφ(x,y), wherein I(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θx, θy in, respectively, the directions of the x and y axes, according to the following formula:
φ(x,y)=−2πh(μ0 tan θx+V0 tan θy).

4 more elements

A deflectometry system for the optical inspection of a phase and amplitude object, comprising:

a grating forming a contrast-based periodic pattern with the spatial frequencies μ0, V0 in, respectively, orthogonal axes x,y in an image plane;
an imaging system comprising an objective and an imaging sensor comprising a plurality of photosensitive elements;
a data processing system connected to said imaging sensor;
and
means for holding said object in an optical path between said grating and the imaging system, at a distance h of said grating;
this deflectometry system being characterised in that said spatial frequencies μ0, v0 are not higher than the respective Nyquist frequencies of the imaging system on said axes x,y, and in that said data processing system is programmed to:
capture through the objective, with the imaging sensor, a first image of said pattern distorted by the phase and amplitude object;
calculate a Fourier transform, in a spatial frequency domain, of said first image of said pattern distorted by said phase and amplitude object;
select at least one first- or higher-order spectrum of said Fourier transform and shifting it in said frequency domain towards a central frequency of said Fourier transform;
and
carry out a reverse Fourier transform of said shifted first-order spectrum of said Fourier transform so as to obtain a complex function g(x,y)=I(x,y)ei φ(x,y), wherein I(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θx, θy in, respectively, the directions of the x and y axes, according to the following formula:
φ(x,y)=−2πh(μ0 tan θx+v0 tan θy).

9 more elements

Dependencies are inferred from the claim text.

Fourier transform deflectometry system and method

Life of this patent

Fourier transform deflectometry system and method

Life of this patent

Abstract

Claims22