Characterization of Fresnel images of an elongated circular grating
Abstract:We characterize theoretically and experimentally Fresnel images (or self-images) of an elongated circular (EC) grating which could be employed for the visual measurement of linear displacements in Talbot moiré deflectometry. Based on a Fresnel diffraction integral, we estimate the shape of the Fresnel image formed at a specific distance from the EC grating in which both parallel lines and semicircles are illuminated by a coherent plane wave. For a square type transmittance of the grating, we also compare the theoretical estimates with its self-images captured by an array of charge-coupled devices (CCD). We show that self-images of the EC grating are substantially aberrated near the center of the interface between the linear and semicircular parts but not in its off-central region. Moiré patterns by two self-imaged EC gratings are found not much affected by the central aberration.
Document Type: Original Article
Publication date: September 1, 2002