Generation Of Structured Light And Measurement Of Topological Charge

Structured light is complex intensity structure beams or complex phase structure light.There are many other types of structured representing different solutions of the underlying wave equation for light in free-space,the Helmholtz equation,that maintains,in general,their shape during propagation.Such beams include the Hermite-Gauss(HG)beams,having multiple intensity lobes;self-accelerating Airy beams,propagating along parabolic caustic trajectories;vortex beams that are characterized by spiral phase wavefront and carry determined orbital angular momentum(OAM)and so on.There are numerous applications because of the uniqueness of structured light,such as the non-contact optical micromanipulation,biological cell handling,laser cooling,atom trapping,quantum informatics,and the control of Bose–Einstein condensates,etc.Vortex beams is the most typical phase-structured beams.In recent years,the vortex beam has received more and more attention,and most researches of the vortex beams are the generate method of vortex beams and the measurement of topologic.At present,the common methods used to generate vortex beams mainly include geometric model transformation,calculation of holographic method,spiral phase plate method,spatial light modulator,rotating mirror optical parametric oscillator method,etc.The methods of measuring the topological charge of vortex beam are interferometric method and diffraction method.The following are the main contents of this paper.Firstly,the basic theory and research progress of vortex beams are systematically summarized in the paper,which expounds the unique beam characteristics and phase characteristics of the optical vortex and its wave front structure,concludes the common methods of generating vortex beams,including diffraction by fork holograms,computing holographic,phase modulation with spiral phase plates,the optical Fourier transform using spatial light modulators,ect.And then it analyzes the principle,application and advantages and disadvantages of various methods.Secondly,this paper proposes a perfect spiral diffraction screen to generate vortex beams,and verified its correctness both from theory analysis and numerical simulation.Compared with the traditional method,using perfect spiral diffraction screen to generate vortex beams is more simple and it can flexibly adjusts the parameter of perfect spiral diffraction screen to generate different shapes and different order of vortex beam.Through this method,the vortex beams with different shapes can be better used as an optical wrench or an optical tweezer to control the particle.Finally,the method of detecting the topological charge of vortex beams based on multiple aperture plane is put forward.It uses different topological charge of vortex as the incident light to illuminate the multiple aperture plane,then we can get the clear light intensity of the diffraction pattern,through analyzing the diffraction pattern to determine the topological charge number of incident vortex beams.This method is not only more simple,but also the measurement range of the topological charge of vortex beam is greatly improved.