Creation of Sub-diffraction Longitudinally Polarized Spot by Focusing Radially Polarized Light with Binary Phase Lens.

An-Ping Yu,Chang-Tao Wang,Xian-Gang Luo,Zhi-Xiang Wu,Yu-Yan Li,Zhi-Hai Zhang,Lu-Ru Dai,Sen-Lin Jiang,Zhong-Quan Wen,Gang Chen,Kun Zhang

doi:10.1038/srep38859

Abstract

The generation of a sub-diffraction longitudinally polarized spot is of great interest in various applications, such as optical tweezers, super-resolution microscopy, high-resolution Raman spectroscopy, and high-density optical data storage. Many theoretical investigations have been conducted into the tight focusing of a longitudinally polarized spot with high-numerical-aperture aplanatic lenses in combination with optical filters. Optical super-oscillation provides a new approach to focusing light beyond the diffraction limit. Here, we propose a planar binary phase lens and experimentally demonstrate the generation of a longitudinally polarized sub-diffraction focal spot by focusing radially polarized light. The lens has a numerical aperture of 0.93 and a long focal length of 200λ for wavelength λ = 632.8 nm, and the generated focal spot has a full-width-at-half-maximum of about 0.456λ, which is smaller than the diffraction limit, 0.54λ. A 5λ-long longitudinally polarized optical needle with sub-diffraction size is also observed near the designed focal point.

Highlights

There is a growing interest in tight focusing of radially polarized light, due to its unique property of a strong longitudinal and nonpropagating electric field in the focal region
We experimentally demonstrated the generation of a sub-diffraction longitudinally polarized spot by focusing radially polarized light with a planar binary phase lens
The focal spot was designed with full width at half maximum (FWHM) of 240 nm (0.38λ), which is smaller than the diffraction limit of 0.54λand the super-oscillation criterion of 0.41λ.Figure 2(a) gives the optimized phase spatial distribution on the planar lens, and its inset shows a zoom-in plot of the phase distribution

Summary

Introduction

There is a growing interest in tight focusing of radially polarized light, due to its unique property of a strong longitudinal and nonpropagating electric field in the focal region. We experimentally demonstrated the generation of a sub-diffraction longitudinally polarized spot by focusing radially polarized light with a planar binary phase lens.

Results

Conclusion