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
Manuel Martínez-Corral, Carlos J. Zapata-Rodríguez, 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)