We compare the Fresnel diffraction pattern of a thin circular disk with that of a square obstacle, specifically evaluating the on-axis field strength. Photographs of the diffraction patterns reveal some curious features for the square obstacle. Second, the precise electric and magnetic fields behind a conducting circular disk are evaluated without invoking the Fresnel approximation and contrasted with the rigorous electromagnetic result for a metal sphere. The calculations show that the two cases differ only slightly in the Fresnel region. In the near-field new computational results for the sphere are analyzed.
© 1988 Optical Society of America
Original Manuscript: September 16, 1987
Published: April 15, 1988
R. Edward English and Nicholas George, "Diffraction patterns in the shadows of disks and obstacles," Appl. Opt. 27, 1581-1587 (1988)