It is shown for the first time we believe, that when a spherical wave illuminates a certain type of diffracting screen, in addition to the expected focal-shift effect, depending on the value of the Fresnel number of the focusing system, a focal switch effect can appear, i.e., an increase in the height of the lateral lobe of the axial-intensity distribution over that of the central lobe.
© 1996 Optical Society of America
Manuel Martínez-Corral and Vicent Climent, "Focal switch: a new effect in low-Fresnel-number systems," Appl. Opt. 35, 24-27 (1996)