title: Continuous numerical aperture properties of a cylindrically polarized light illuminated sub-wavelength annular aperture.
abstract: We investigated the process of focusing a radially polarized (RP) light beam through a sub-wavelength annular aperture (SAA). We found that the result was a non-diffraction doughnut-shaped light beam which propagates in free space. After analyzing the electric field component of the focus generated by the SAA structure, we identified the relationship between the focal field generated by the SAA. We then compared it to a case with a traditional objective lens. From our findings, we propose that a SAA structure can be viewed as a continuous numerical aperture optical element.
authors: Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan.
authors: Chun-Chieh
authors: CC
authors: Fang
authors: Tsung-Dar
authors: TD
authors: Cheng
authors: Jyi-Tyan
authors: JT
authors: Yeh
authors: Kuang-Chong
authors: KC
authors: Wu
authors: Chih-Kung
authors: CK
authors: Lee
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007909:Lenses; D008027:Light; D008029:Lighting / Q000295:instrumentation*; D008962:Models, Theoretical; D055096:Optical Devices; D012031:Refractometry / Q000295:instrumentation*; D012542:Scattering, Radiation; D020349:Surface Plasmon Resonance / Q000295:instrumentation*