Properties And Applications Of Vector Fields And Optical Tweezers

With the development of laser technology and laser photonics, the photon, one of the most basic carriers of information, by contributing to much finding of new phenomena and novel effects, is playing more and more role in modern scientific and technological research, such as in national security, medicine, material processing and information processing. To take full advantage of photon and related novel effects and phenomena, the key is to manipulate the optical field. The character of light involving the phase, frequency and amplitude have been deeply explored and widely used. The vector fields as well as the manipulation of polarization state have attracted more and more interest in recent years and the research on vector fields is getting more and more attention. The inhomogeneous polarization distribution of vector field makes a great impact on the spatial-temporal evolution and the interaction of light with matter. Just name a few examples:the radially polarized field could be highly focused into a sharper spot with with subdiffraction beam size; the localized field enhancement can be realized by the use of plasmonic lens illuminated by the radially polarized field and the spatial distribution of polarization could offer another freedom for the photon entanglement; the curl of polarization could result in a new category of optical orbital angular momentum. Moreover, the capability of shaping the focal volume can be exploited for optical manipulation. The radially polarized beam has a higher trapping efficiency than the linearly polarized beam, and optical cage generated by cylindrical vector beams has the trapping capability of the low-refractive-index particles. However, the research of vector fields is fresh and there remain many scientific and technological problems to be solved. This dissertation is mainly focused on the generation, manipulation and application of the vector field and novel3D optical tweezers. The main contributions of this dissertation are as follows:1. The method to generate novel vector fields is proposed. After a review of methods to generate vector fields have been reported, we propose a convenient approach for generating arbitrary space-variant vector beam with structured polarization and phase distributions in a4f system with a spatial light modulator (SLM) and a common path interferometric arrangement. In substitution of conventional1-dimension holographic gratings with2-dimentions, phase structure of vector field is enhanced. Take advantage of SLM, optical realization of vector fields with a variety of polarization and phase configurations is obtained dynamically by modulating2D holographic grating.2. The focal properties of vector fields are discussed and the optimized design of target focal field is proposed. The mathematical derivation of the Richards-Wolf vector theory, which is used to calculate the focal properties, is carried out. We present a fast calculation of the electromagnetic field near the focus based on angular spectrum theory by using the fast Fourier transform (FFT) method. We proposed a polarization-only method of polarization shaping in the focal region with the polarization modulation of incident light. By using an iterative optimization based on a vectorial diffraction calculation relating the incident field to the focal field with the help of the FFT, we can tailor the polarization structure in the focal plane. This provides a novel way to control the vectorial feature of the focal volume with the help of polarization tailoring. Based on the method to generate the vector beams with the phase and the polarization modulated independently, the ability and flexiblity to tailor the feature of the focal volume is verified by optical experiments.3. We show that the separation of spin angular momentum flux in the focal region can occur at the focal plane illuminated by a space-variant linearly polarized beam. Such a beam carrying only the orbital angular momentum (OAM) but no SAM can develop a net SAM flux upon focusing. The radial split of the SAM flux density is mediated by the phase vortex (or OAM) and can be controlled by the topological charge of the phase vortex. The numerical simulation and the optical trapping experiment have been performed to validate the separation of the SAM flux density and spin-to-orbital conversion. Also, the radius of the focal ring is influenced by the of spin-orbital interaction in the tightly focused condition. The rotation cycle of the trapped liquid crystal particle is observed for comparison by changing the topological charge of polarization and phase.4. Theory and experiment of novel three-dimensional(3D) holographic tweezers is explored. We incorporate3D FFT into the design of holographic tweezers and propose a novel3D holographic tweezers. With our novel iterative algorithm that is based on a close inspection at the3D Fourier transform for synthesizing optical beams in the focal volume, a continuous intensity shaping within a volume becomes available. This method, which is different from the reported method of optical shaping dealing with discrete planes with2D FFT, provides a new way to develop3D-holographic optical tweezers. The perfomance of this method in optical tweezers for optical trapping and particles stacking in order are also demonstrated in our optical experiments.