Super-resolution longitudinally polarized light needle achieved by tightly focusing radially polarized beams

Abstract

Based on the vector diffraction theory, a super-resolution longitudinally polarized optical needle with ultra-long depth of focus (DOF) is generated by tightly focusing a radially polarized beam that is modulated by a self-designed ternary hybrid (phase/amplitude) filter (THF). Both the phase and the amplitude patterns of THF are judiciously optimized by the versatile particle swarm optimization (PSO) searching algorithm. For the focusing configuration with a combination of a high numerical aperture (NA) and the optimized sine-shaped THFs, an optical needle with the full width at half maximum (FWHM) of 0.414λ and the DOF of 7.58λ is accessed, which corresponds to an aspect ratio of 18.3. The demonstrated longitudinally polarized super-resolution light needle with high aspect ratio opens up broad applications in high-density optical data storage, nano-photolithography, super-resolution imaging and high-efficiency particle trapping.