Focusing Study On Vector Polarized Beam

Polarization is an important property of light. Unlike the beam withspatially uniform polarization, vector polarized beam is a class of laser beam withspatially nonuniform polarization. One particular example is cylindrical vector beamwhich has cylindrical symmetry in both polarization and amplitude. If cylindricalvector beam is focused by a high-numerical-aperture objective, a strong longitudinalelectric field is obtained. Due to this strong longitudinal component, a small focalpattern can be generated. This peculiar focused property is of great interests to manyapplications in various field such as high resolution imaging，optical tweezers system,data storage and so on. In addition, The generalized cylindrical vector beam can bedecomposed into a linear superposition of radially polarized and azimuthallypolarized components. To adjust the ratio of radial and azimuthal polarizationcomponents, a flat-top focus can be obtained hence achieving a potential goal ofbeam shaping. Vector polarized beam is a generalized conception with high value inresearch and recently the study of it in theory and experiment is continuously goingon.The thesis mainly concentrates on the works as the followings:1、Based on vector diffraction theory, three cases of cylindrical vector beam aresimply introduced, including radially polarized beam, azimuthally polarized beamand generalized cylindrical vector beam. The intensity distribution near the focus isanalyzed from the Debye integral and the focusing properties is discussed. Also,some applications in cylindrical vector beam are introduced.2、Using the phase-only filter, the wavefront phase of incident cylindrical vectorbeam is modulated into two portions, the center circle portion and outer annularportion. Increasing the radius of the center circle with л phase shift, the maximumintensity ratios of the radially polarized field to longitudinally polarized field in focalregion are investigated theoretically. The maximum intensity ratio can be altered fordesirable motive in application.3、A kind of continuous phase-only filter with cosine function is designed forcylindrical vector beam to achieve super-resolution in the focal plane. The resultsshow that there is a significant improvement on sharper focus with this type filter. 4、Focus shaping technique using generalized cylindrical vector beam isinvestigated theoretically. The generalized cylindrical vector beam can bedecomposed into a linear superposition of radially polarized and azimuthallypolarized components. Adjusting the ratio of radial and azimuthal polarizationcomponents, focus can be shaping, hence achieving a potential goal of beam shaping.The effect of radially polarized and azimuthally polarized components with differentNA values for a flat-top focus is studied.