Topological Charge Of The Vortex Beam Measurements

Since the discovery of vortex beams, the transmission has been widely concerned. The study of vortex beams became more and more importance. A vortex beam has a spiral phase wavefront exp(ilθ), each photon of the vortex beam possesses lh OAM (l is called the topological charge). Such vortex beams have special applications in many areas, such as the control of micro-particles biomedicine, and information encoding. Therefore, vortex beams has a wide range of applications.In this work, we study the generation of vortex beam, the transmission characteristics and the measurement methods of the topological charge of vortex beams. The measurement of vortex beams of fractional topological charges is investigated in great detail. The main contents of this dissertation are organized as:1,Vortex beams are obtained by use of holographic method. Firstly, the computer-generated hologram (CGH) of the interference pattern of vortex beams with plane wave is numerical simulated, and is loaded onto the spatial light modulator (SLM). The vortex beam is generated as a plane wave incident on the SLM. Vortex beams with different topological charge can be obtained by changing the CGH.2,We theoretically and experimental study the generation and interference of vortex beams. In theory, the interference of integral and fractional topological charges vortex beams with the spherical wave and the plane wave has been studied. We obtained the interference patterns, the experimental results are in consistent with the theoretical results. It is found that the interference patterns will change with the change of the topological charge of vortex beams. Based on the results, We can measure the topological charges of vortex beams.3,We study the diffraction characteristics of vortex beam through the circular aperture.The purpose is based on diffraction patterns obtained to determine the number of vortex beam of topological charge. The diffraction of vortex beam through a circular aperture is investigated theoretically and experimentally and the outcome can be achieved through experiments. The influence of the topological charge (including integer and fraction) of vortex beams on the diffractive pattern are studied in great detail. The results may have potential application in determination the topological charge of vortex beams4,The topological charge of integral vortex beams with a single circle of multipoints has previously been measured. In this work, we theoretically and experimental study the diffraction patterns of vortex beams of integral and fractional topological charges using a single circle and two circles of multipoint plates. It is found that the diffraction patterns are dependent not only on the multipoint plates, but also on the topological charge of the vortex beams. On the basis of this property, we can measure the topological charges of integral and fractional vortex beams.5,A novel slit with angular transmittance is proposed and the interference patterns of a vortex beam transformed through the angular slit are investigated theoretically and experimentally. The theoretical results are simulated based on the intensity expression in the far field, which are in consistent with the experimental results. It is shown that, the interference pattern depends on the number of the angular slit and the topological charge of vortex beams. The result may have potential application in measuring the topological charge of vortex beam.