Abstract

Gaussian beams that are focused by apertured lenses produce diffraction patterns in the near field. These diffraction patterns differ from the plane wave diffraction patterns: the axial minima are not as dark and the axial maxima are not as intense. In addition, the shift of the point of maximum intensity from the location of the geometrical focus depends on the ratio of the aperture radius to the Gaussian radius. The diffraction patterns almost disappear for ratios larger than 2. In cases where the aperture is not circular the effective radius of the aperture becomes the relevant parameter. An investigation of the aspect ratio of the rectangular aperture on the diffraction pattern is provided. The numerical calculations are based on the Kirchhoff’s diffraction integral. There was an attempt at reducing the impact of phase approximations on the predicted intensity pattern.

© 1991 Optical Society of America