Statistical Characteristics Of Rotating Gaussian Schell-model Beams And Their Orbital Angular Momentum Properties

As is known to us,compared with a fully coherent case,partially coherent beams have shown many intriguing characteristics and advantages in practical applications.Coherence and phase structure are two important parameters in light field modulation.With the development of science and technology and the improvement of production and living needs,the properties of light field are supposed to be optimized and diversified.The modulation of spatial correlation function is a common and effective way in light field modulation.As the research on partially coherent beams progresses,in addition to the traditional Gaussian correlation function,the partially coherent beams with unconventional correlation structures have attracted extensive attention due to the special properties,such as self-focusing,self-splitting,self-drifting and so on.Therefore,it has potential application values in the fields of beam shaping,optical communication,optical tweezers and super resolution imaging.Moreover,the modulation of spatial phase structure is also a significant research orientation.In recent years,there has been a great interest in the beams carrying the orbital angular momentum(OAM),such as the vortex beams with helical phase structure,the twisted Gaussian Schell-model beams and so on.The unique OAM properties of such beams provide great prospects in the fields of particle manipulation,quantum information processing and optical communication.In this dissertation,we focus on the OAM characteristics and propagation properties in free space of the asymmetric twisted vortex Gaussian Schell-model(ATVGSM)beams,and analyze the behaviors of the correlation singularities in detail.Furthermore,we also investigate the focusing properties of a rotating anisotropic generalized multi-Gaussian Schell model(RAGMGSM)beam and consider the radiation forces acting on Rayleigh particles.The dissertation chapters are arranged as follows:Chapter 1 contains two parts.In the first part,we firstly introduce the research background of the theory of partially coherent beams,and then arrange the research processes and development tendency related to the content of this dissertation from four aspects:unconventional correlation structure,optical vortices and coherent vortices,twisted Gaussian Schell-model beams and the technique of optical tweezers.The second part gives the theoretical basis and research methods mainly involved in this dissertation:the representation form of partially coherent beams,the generalized diffraction integral formula,the theory of OAM and the radiation forces on a Rayleigh dielectric particle.In chapter 2,we analyze a family of asymmetric twisted vortex Gaussian Schell-model(ATVGSM)beams,which are derived via a coupling of off-axis vortex phase and twist phase in the correlation function.Explicit expression of the orbital angular momentum(OAM)carried by such a beam is derived and the impact of the state of coherence on the OAM is demonstrated.Further,the evolution of the intensity distribution and the behaviors of the coherence vortices during propagation are explored in detail.It is shown that owing to the shift of the vortex phase dislocation such a beam has the form of a crescent,which rotates upon propagation.The stability of the asymmetric dark hollow structure is deeply affected by the interaction of two kinds of phases and the change of state of coherence is induced by the twist strength.Meanwhile,the coherence vortices generate in pairs with opposite topological charge and move along certain trajectories under various conditions.Besides,the expression related to define the rotation angle is deduced and the rotating properties of the intensity pattern are discussed.In chapter 3,we investigate the focusing properties and the radiation forces produced by a focused rotating anisotropic generalized multi-Gaussian Schell model(RAGMGSM)beam.We find that due to the existent of the twist term,it would produce a twist of the beam upon propagation.For different parameters at the trapped plane,the intensity distribution would evolve into an elliptical dark hollow or elongated Gaussian beam profile.Compared to the focal plane,the trapped plane has an axial displacement due to the twist effects.Further,we demonstrate that two types of particles at different positions of the trapped plane can be trapped and rotated simultaneously by such a focused beam.Moreover,the influences of the beam index M,the coherence width δ,and the twist factor u on the radiation forces is elucidated respectively.The limits of each parameter for stability of optical trapping under a certain condition are explicitly discussed.Chapter 4 summarizes the main conclusions and innovations of this thesis and the prospect of future work is given.