Spatially variant polarization has stimulated continuous research interests due to its peculiar properties in focusing and surface plasmon excitation, providing broad applications in optical data storage, nano-fabrication, particle trapping, high resolution microscopy and metrology. In this dissertation, focus shaping, three dimensional (3D) state of polarization control, and plasmonic focusing with spatially variant polarization are investigated and demonstrated both theoretically and experimentally.
This research shows that 3D flattop focusing with extended depth of focus and optical bubble can be obtained using the combination of generalized cylindrical vector beams and diffractive optical element. Through combining the electric dipole radiation and the Richards-Wolf vectorial diffraction method, the input field at the pupil plane of a high numerical aperture objective lens for generating arbitrary three dimensionally polarization at the focal point with an optimal spot size can be found analytically by solving an inverse problem.
In additional to focusing with high numerical aperture lens, spatially variant polarization has great advantage in surface plasmon focusing. Optimal plasmonic focusing can be achieved through matching the polarization symmetry of a radially polarized illumination to axially symmetric dielectric/metal plasmonic lens structures. Three types of plasmonic lens have been studied in this research. Experimental realization of the nondiffracting evanescent Bessel beam generation via surface plamson resonance excitation on homogeneous metallic thin film with radially polarized beam illumination is first demonstrated. Then, plasmonic lens with annular rings under radial polarization illumination is studied. It is found that higher field enhancement factor can be achieved with increasing number of rings in the plasmonic lens. Finally, an apertureless near-field scanning optical microscope probe under radial polarization illumination is numerically studied with 3D finite element method model. The field distribution with a full-width-half-maximum as small as 10 nm and intensity enhancement of five orders of magnitude can be achieved with 632.8 nm optical excitation. Preliminary experimental results using Raman spectroscopy with the designed apertureless tip confirmed the field enhancement through comparing the near field and far field signals.