Longitudinally polarized electric and magnetic optical nano-needles of ultra high lengths

We demonstrate a method to generate longitudinally polarized electric and magnetic light spots over ultra-long distances. The method proposed here relies on the generation of radially and azimuthally polarized Bessel beams at the limit between propagating and evanescent regimes, by projecting radially and azimuthally polarized doughnut beams onto an axicon-based system of numerical aperture (NA) equal to 1. Tight electric and magnetic light spots (0.36 gimel) can be produced over distances reaching 50,1 and with longitudinal intensities about 3.5 x 10(4) times above the transverse intensities. Same confinement abilities over distances larger than 335 A is also predicted with longitudinal intensities 883 fold above the transverse ones. Experimental characterization of these tiny optical needles with polarization-resolved heterodyne SNOM reveals electric and magnetic light spots smaller than 0.4 gimel whose longitudinal intensities are about 200-fold larger than the transverse ones. (C) 2013 Elsevier B.V. All rights reserved.