Affiliation:
1. The George Washington University
Abstract
Light from any physical source diffracts over space, as spherical wavefronts grow and energy density is spread out. Diffractive effects pose fundamental limits to light-based technologies, including communications, spectroscopy, and metrology. Polarization becomes paraxial in the far-field limit, and, by ignoring longitudinal field components, the rich physics of non-paraxial fields that exist in near-fields or a beam’s tight focus is lost. The longitudinal field cannot, however, be ignored when transverse field components vanish (in a transverse field zero) and carry a small non-paraxial region to infinity. We show that a transverse field zero is always accompanied by non-diffracting polarization structures, whose geometries are independent of the distance to the source, including an enclosing intensity ratio tube, and parallel, non-diverging polarization singularities. We illustrate these features in multipole radiation and in double-slit interference, two examples that have time-fixed transverse field zeros. Non-diffracting structures with a changing position are coupled to time-varying zeros, which are present in all far-field radiation.
Funder
Army Research Office
Engineering and Physical Sciences Research Council
Subject
Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials