Martínez Herrero, RosarioCarnicer, ArturJuvells, IgnasiSanz Ortiz, Ángel Santiago2023-06-172023-06-172020-09-291094-408710.1364/OE.401073https://hdl.handle.net/20.500.14352/7534© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. Agencia Estatal de Investigación and European Regional Development Fund (FIS2016- 75147-C3-1-P, FIS2016-76110-P, PID2019-104268GB-C21, PID2019-104268GB-C22).In the analysis of the on-axis intensity for a highly focused optical field, it is highly desirable to deal with effective relations aimed at characterizing the field behavior in a rather simple fashion. Here, a novel and adequate measure for the size of the region where the axial power content mainly concentrates is proposed on the basis of an uncertainty principle. Accordingly, a meaningful relationship is provided for both the spread of the incident beam at the entrance of the highly focused optical system and the size of the region where the on-axis power mainly concentrates.engAtribución 3.0 Españajournal articlehttp://dx.doi.org/10.1364/OE.401073https://www.osapublishing.orgopen access535Spatial-directional localizationFilter performance parametersNonparaxial fieldsLightBeamsdiffractionCoherentSystemsÓptica (Física)2209.19 Óptica Física