We report on an analytical formulation, based on the concept of effective Fresnel number, to evaluate in a simple way the relative focal shift of rotationally nonsymmetric scalar fields that have geometrical focus and moderate Fresnel number. To illustrate our approach, certain previously known results and also some new focusing setups are analytically examined.
© 1998 Optical Society of America
Original Manuscript: April 25, 1997
Revised Manuscript: August 7, 1997
Manuscript Accepted: August 11, 1997
Published: February 1, 1998
Manuel Martı́nez-Corral, Carlos J. Zapata-Rodrı́guez, Pedro Andrés, and Enrique Silvestre, "Effective Fresnel-number concept for evaluating the relative focal shift in focused beams," J. Opt. Soc. Am. A 15, 449-455 (1998)