Focusing of vector beams with fractional-order azimutal polarization

Abstract

By simulating sharp focusing of vector beams with azimuthal polarization of fractional order 0 < m <1 (m = 1 is azimuthal polarization, m = 0 is linear polarization), it was shown that the shape of the intensity distribution in the focal spot changes from annular (m = 1) to round (m = 0.5) and then to elliptical ring (m = 0). The opposite changes we can see for the shape of the distribution of the longitudinal component of the Poynting vector (energy flux) in the focal spot: from annular (m = 1) to elliptical (m = 0.5) and then to circular ring (m = 0). The diameter of the focal spot at full width at half maximum for a beam with azimuthal polarization (m = 1) with an optical vortex of the first order for a numerical aperture NA = 0.95 is 0.46 of the wavelength, and the diameter of the axial energy flux for linearly polarized light (m = 0) is 0.45 of the wavelength. Because of this, the answers to the questions: Whether the focal spot is round or elliptical and whether the focal spot is minimal: with azimuthal polarization with a vortex or with linear polarization without a vortex, depend on whether we are considering the intensity at the focus or the energy flow.