Research On The Generation,Propagation And Trapping Properties On A Rayleigh Particle Of Special Beams

In recent years,due to the enrichment of control methods for light fields,some light fields with special structures have attracted the interest of many researchers.Among them,the abruptly autofocusing beam is one of the research hotspots.It can be used for particle trapping and manipulation,and compared with the traditional Gaussian beam,the abruptly autofocusing beam can effectively improve the performance of optical tweezers.On the other hand,vortex beams carry orbital angular momentum.It plays an important role in optical communication,particle manipulation and capture and quantum information processing.If the abruptly autofocusing beam is taken as the background field of optical vortex,one can combine the advantages of the two to provide an important theoretical basis for the application of particle manipulation,information transmission and bioengineering.Based on above research background,this thesis takes abruptly autofocusing beams and vortex beams as research objects.The laser propagation theory,partially coherent theory,and radiation force theory are combined with experimental methods to study multiple circular Airy beams with lens phases,partially coherent radially polarized circular Airy vortex beam,vortex beam with multiple rotational phase singularities,ring-arrayed Pearcey-Gaussian vortex beams and radiation forces on a Rayleigh particle produced by partially coherent circular Airy beams,respectively.The chapters of this paper are arranged as follows:Chapter 1 is the introduction of this thesis.The research background and development status of two autofocusing beams,i.e.Airy beam and Pearcey beam,and vortex beam are introduced.The basic theories involved in this paper are given,including the laser propagation theory,the radiation force theory and the basic theory of partially coherent beams.At the same time,the experimental method involved in the research is introduced,the research purpose and the content arrangement of each chapter are pointed out.Chapter 2 introduces multiple circular Airy beams carrying lens phases.Multiple circular Airy beams are generated by regional coding,and the lens phase makes the beam exhibit multiple foci,higher focusing ability and double focusing properties during the propagation.Experimentally,the spatial light modulator was used to generate such a beam and the propagation properties of the beam were verified.Chapter 3 introduces partially coherent radially polarized circular Airy vortex beams.Firstly,the quadruple integral of cross spectral density matrix,which is used to describe the intensity distribution for the propagation of partially coherent beam,is simplified into a double integral form.Based on theory and experiments,the influence of topological charge and coherent width on the intensity distribution on the focal plane,autofocusing ability,polarization degree distribution,intensity distribution of fully polarized part and unpolarized part are studied in detail.At the same time,the polarization transition phenomenon is analyzed by simulating the polarization state distribution of the beam.Chapter 4 introduces the vortex beam with multiple rotational phase singularities.Firstly,the analytical propagation expression of the beam is given.Then,the intensity and phase distributions of the beam propagating in free space are studied.Theoretical simulations are combined with experimental verifications to analyze the influence of topological charge,separation strength factor and angle-control factor on the propagation characteristics of the beam.In addition,the energy flow density and orbital angular momentum density distributions of the beam are given.Chapter 5 introduces the ring-arrayed Pearcey-Gaussian vortex beam.The autofocusing properties of beams without vortices,with an on-axis vortex,with an offaxis vortex and double vortices are studied.The influence of topological charge and focusing factor on autofocusing ability,intensity distribution and focusing distance are analyzed.In addition,experiments are carried out to verify the simulation results.Chapter 6 studies the radiation force of partially coherent circular Airy beams on a Rayleigh particle.The effects of spatial coherence width,scale factor and initial radius on the radiation force and the number of trapping points are studied,and the trapping stability of the beam on the particle under different coherence widths is analyzed.Chapter 7 summarizes the main work and innovations of this thesis,and makes a prospect for the future studies.