Impact of aperture thickness on a Fraunhofer diffraction pattern

Abstract

In this paper, we investigate in detail the effect of increasing aperture thickness on a Fraunhofer diffraction pattern. The scalar diffraction theory is employed to derive the solution of the far-field amplitude for a single-slit and a circular aperture in both normal and oblique incidents. Our results show that increasing the aperture thickness indisputably modifies the diffraction pattern, mainly for the wide apertures. It is proven that the maximum value of the diffracted field amplitude decreases for the non-zero values of the aperture thickness, resulting in the reduction of the fringe visibility. This study reveals that in the case of the single-guided-mode operation, the diffraction pattern is independent of the incident beam direction, and is the same for an aperture thickness larger than the attenuation length of the first evanescent mode. On the contrary, it is observed that the diffraction pattern of a wide aperture at the oblique incidence is entirely different from the popular laterally shifted normal incident diffraction profile. Therefore, we conclude that it is impossible to carefully examine the diffraction phenomena, without considering the effect of the aperture thickness.