Abstract

When an inhomogeneous plane wave or other type of evanescent field in a lossless medium strikes a large opaque object, the boundary of the shadow zone is displaced from the familiar geometric optical location for nonevanescent fields. This change is attributable to the complex propagation direction of evanescent waves. To study the mechanism of shadow formation, and indeed the significance of a shadow zone when the incident evanescent field may be weaker than diffracted fields generated by the obstacle, the problem of inhomogeneous plane diffraction by a perfectly conducting semi-infinite screen is investigated. By a careful asymptotic treatment and error analysis of the known exact solution, the location of the shadow boundary is determined, as is the transition region surrounding it wherein the field cannot be separated into incident and diffracted constituents. It is found that for strongly evanescent fields, the shadow boundary and transition zones differ markedly from those for a homogeneous plane wave. Effects of losses in the medium are also considered.

© 1978 Optical Society of America

Properties of the shadow cast by a half-screen when illuminated by a Gaussian beam

Arthur C. Green, Henry L. Bertoni, and Leopold B. Felsen
J. Opt. Soc. Am. 69(11) 1503-1508 (1979)

Errata: Shadowing an Inhomogeneous Plane Wave by an Edge

Henry L. Bertoni, Arthur C. Green, and Leopold B. Felsen
J. Opt. Soc. Am. 68(12) 1787_2-1787 (1978)

Asymptotic representation of the boundary-diffraction wave for a three-dimensional Gaussian beam incident upon a Kirchhoff half-screen

Takashi Takenaka and Otozo Fukumitsu
J. Opt. Soc. Am. 72(3) 331-336 (1982)

Asymptotic representation of the boundary diffraction wave for a Gaussian beam incident on a circular aperture

Takashi Takenaka, Masao Kakeya, and Otozo Fukumitsu
J. Opt. Soc. Am. 70(11) 1323-1328 (1980)

Asymptotic solution for the diffraction of an electromagnetic plane wave by a cylinder-tipped half-plane

Y. T. Chu, V. E. Anderson, H. H. Hubbell, and T. L. Ferrell
J. Opt. Soc. Am. 73(6) 768-775 (1983)