A new and simple formula valid within the framework of the Debye theory is derived for determining the structure of focused fields in diffraction-limited systems. It is first applied to study the field behavior in the focal region, and the results are compared with those of the classic theory of Lommel. The field distribution in the intermediate zone between the focal region and the far zone is then studied, and the changes of the field with increasing distance from the geometrical focus are examined. An estimate is obtained for the distance from focus at which the field behaves as a cutoff portion of a uniform spherical wave.
© 1995 Optical Society of America
Original Manuscript: January 31, 1995
Manuscript Accepted: April 12, 1995
Published: September 1, 1995
Weijian Wang, Ari T. Friberg, and Emil Wolf, "Structure of focused fields in systems with large Fresnel numbers," J. Opt. Soc. Am. A 12, 1947-1953 (1995)