Method For Probing The Orbital Angularmomentum Of Optical Vortices And Optical Trapping Of Nanoparticles

Vortex beam is a kind of special beam with helical phase wave-front. Since it proposed, vortex beams has aroused wide attention of researchers. The phase distribution function of vortex beams often contains spiral phase factor exp(ilθ),that is proportionate to rotation azimuth angle. l is the topological charge of vortex beams. In 1992, Allen et al. demonstrated that optical vortex with a phase factor exp(ilθ) carry orbital angular momentum l in the paraxial propagation conditions. Different from traditional beams, the vortex beams have phase singularities and orbital angular momentum, when propagating. That forms dark hollow vortex spot in the center of its intensity. Because of the many unique features, vortex beams have important research significance and application value in the field of photonic communications, information coding, optical micro-manipulation etc. Further study of the vortex beam will greatly promote the development of science and application research of our country. This paper studies the method to measure the topological charge of the vortex beam and the capture and manipulation the metal nanoparticles with anomalous vortex beams. The main contents are as follows:1. This thesis first gave a brief introduction to the optical vortex, the present situation of the research of optical vortex, and the significance of this thesis. Further the thesis introduced the theoretical basis of and vortex beam transmission and the theoretical models of optical tweezers transmission optical tweezers vortex beam.2. The phase distribution function of vortex beams often contains spiral phase factor exp(ilθ),that is proportionate to rotation azimuth angle. l is the topological charge of vortex beams. Widely used in information coding and optical communication, measuring the topological charge of vortex beams is of great importance. We studied the transmission characteristics of Laguerre-Gaussian vortex beams passing through symmetric acute pyramids and analyzed the intensity distribution of vortex beams interference. On the basis of this study, we tried to propose a new approach to measure the topological charge of vortex beams. After numerical simulation and experimental verification, we proved that this method is effective and feasible.3. Then we studied the capture and control of metal nano-particles with anomalous vortex beams. Anomalous vortex beams is a new kind of vortex beams and the characteristics of optical tweezers should be placed close attention on. We found that anomalous vortex beams with certain topological charge and the order can capture and manipulate metal nano-particles successfully and stably. At last we analyzed the conditions of capturing particulates stably.