Analysis of wave aberration influence on reducing focal spot size in a high-aperture focusing system

It was shown that the addition of transmittance functions corresponding to the wave aberrations in the form of Zernike functions to the high-numerical-aperture focusing systems results in narrowing of the transverse dimension of focal spot below the diffraction limit. Moreover, for linear polarization, the most common for modern lasers, the results achieved along one direction are better than for the radial polarization, obtaining of which requires complex or expensive devices. Overcoming of the diffraction limit happens due to a substantial reduction of energy in the central part of the focal region. However, the possibility of registration of light fields that have a very low intensity provides perspectives of the received results. For linear polarization an elongated focal spot that has full width at half of maximum along the polarization axis FWHM( )=0.24lambda was obtained, for the radial polarization a round spot that has FWHM=0.35lambda and also for the circular polarization with FWHM=0.35lambda was obtained. For the azimuthal polarization the vortex phase function of the first order allows us to obtain the total intensity of the central circular spot of light narrower than the diffraction limit: FWHM=0.46lambda with low intensity in the sidelobes. It was also shown that not only the size of light spot can be reduced, but also the shadow area, formed by a light ring with very small radius.