Radiation patterns of an elliptical aperture in the Fresnel region

The Fresnel diffraction of a coherent light beam due to an elliptical aperture with the axial ratio (epsilon) between 1.0 and 0.5 is investigated. The computations are based on a procedure due to Hopkins (1957). Perspective plots of the intensity-distribution diagrams are generated for Frensel number (F) = 5 and the axial ratio (epsilon) = 1.0, 0.5, respectively. The results are compared with the corresponding diagrams for the circular aperture. With the decreasing axial ratio, it is observed that the central maxima and minima disappear in contrast to that of the circular aperture, whereas a modulation in the central region along with the side maxima is found. Also given are the plots of the intensity distribution on the optical axis.