Reduction of the focal spot size in high-aperture focusing systems at inserting of aberrations

Abstract

Possibility of control by the contribution of components of vector electric field in focal area by means of transmission functions similar to the wavefront aberration for the purpose of reduction of the cross-section size of the central light spot of focusing system with the high numerical aperture is shown. By analysis of a matrix of polarizing transformation of a high-aperture lens and numerical modeling of focusing system in Debay approach the possibility of reducing the size of the focal spot and shadow area is proved. Efficiency of use Zernike polynomials for formation of a subwavelength central spot is shown: elongate focal spot having full width at half maximum along polarization axis FWHM(?) = 0.24? is obtained for linearly polarized beam; round focal spot having full width at half maximum FWHM = 0.35? is obtained for radially polarized beam and FWHM = 0.35? for circularly polarized beam. For the azimuthal polarization the presence of the first order vortex phase function enables us to obtain the central circular spot in the total intensity. The spot is smaller than the diffraction limit: FWHM = 0.46? and the intensity in the side lobes is low. A shadow zone with a diameter VD = 0.5? is formed for radial polarization and with small dark spot in longitudinal component (VDz = 0.44?) is received.