Moiré Pattern of Two Fresnel Zone Plates
The Moiré pattern formed using two displaced Fresnel zone plates illustrates the straight line interference fringes produced by interfering two spherical waves having the same radius of curvature. The spacing of the straight line pattern depends on the separation between the centers of the two Fresnel zone plates, just like the spacing of interference fringes depends upon the separation between the two point sources.
Moiré patterns are a good way to illustrate the interference of two wavefronts. Moiré patterns show the difference between the two original patterns just like interference fringes show the phase difference between two interfering wavefronts. When the two patterns are in phase, bright regions result and when the patterns are a half-period out of phase, dark regions result.