Formation, Properties And Applications Of Axially Symmetric Polarized Beams

Axially Symmetric Polarized Beams (ASPBs) are space variant polarized beams with axial symmetry, whose symmetry axis is the propagation axis of the light beam. Due to their unique optical properties, such beams have many potential applications in imaging, optical trapping, material processing, surface plasmon excitation, and so on. In the dissertation, the generation methods, optical properties and potential applications of ASPBs have been studied on the basis of the analysis of state of the art.Based on the polarizing beam splitting properties of subwavelength metallic gratings, the generation method of radially polarized beams and high order polarized beams in the visible range using segmented subwavelength metallic gratings (SSMGs) is proposed. The structure parameters of SSMGs are optimized using Fourier Modal Method (FMM), and the polarization transformed devices of space variant polarized beams with the orders 1, 2, 3, and 4 are fabricated by Tsinghua Foxconn Nanotechnology Research Center. The phase distribution of transmitted beams is analyzed, and the intensity and polarization distribution of transmitted beams are also measured based on Stokes measurement method. The polarization purity of the generated radially polarized beam is 94.8%, and the numbers for transformed P=2, 3, 4 space variant polarized beams are 90.4%, 89.3%, 81.7% respectively. The SSMG devices can operate in a wide wavelength range, and show a broadband achromatic property in visible range.The mathematical expressions of focused fields of ASPBs in free space have been derived based on vectorial diffractive theory. The amplitude, intensity, phase and polarization distributions of focused field of different types of ASPBs have been numerically calculated, which show the high NA focusing fields of higher polarization order ASPBs have strong axial components and present multiple superresolution spots near focus. The number of focal spots is related to the polarization order P as 2×(P 1). The focused beams are still axially symmetric, but present polarization singularities and phase singularities in some spatial positions. An optical measurement system is built based on a confocal microscope, and the high NA focused field intensities of radially polarized beam and azimuthally polarized beams are measured, and the measurement results verify the theoretical analysis.3D focus shaping using diffractive optical elements (DOEs) is studied, and DOEs for some special field distributions, such as flat top, optical chain and ultra small focal spots with long depth of focus, have been designed. Meanwhile, an optimum design method for diffractive superresolution elements for radially polarized beam is also studied.Two methods to implement optical trapping using ASPBs are discussed. Multiple ultra small focusing spots of high NA focused ASPBs formed near the focal plane can trap multiple micro particles simultaneously, and surface plasmon interfering fields excited by tightly focused ASPBs can trap multiple particles near the metal film as well. The basic theories for both methods are presented, and some simulations are carried out to verify the feasibility of the methods.