Subwavelength focusing of azimuthally polarized optical vortex

In this work, we numerically investigated focusing of a quasi-cylindrical optical vortex with azimuthal polarization and a wavelength of 532 nm. It was shown that the focal spot produced by a beam with four sectors focused with a Fresnel zone plate with a numerical aperture of NA = 0.95 does not differ from the ideally azimuthally polarized optical vortex; the difference in the focal spot diameter does not exceed 0.03λ. The four-sector binary subwavelength grating polarizer was fabricated in a golden film. It was experimentally demonstrated that a linearly polarized 532-nm Gaussian beam reflected at the polarizer was converted to an azimuthally polarized beam. Putting a spiral phase plate (SPP) with the topological charge n = 1 into the azimuthally polarized beam from the micropolarizer was experimentally shown to enable the conversion of the annular intensity pattern into a central intensity peak.

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