Study Of The 4Pi Focusing Properties Of Radially Polarized Vortex Optical Field

Polarization is an important property of light.The polarization state of the vector optical field varies with the space in the cross section of the optical field,so it needs the vector theory of the optical field to characterize it.The common cylindrical vector optical field has radial polarized optical field and angular polarized optical field.In this paper,the radial polarized optical field is modulated by the diffraction optical element(DOE)and the high numerical aperture(NA)lens system,so as to obtain optical structures such as optical sphere,optical cage,optical chain,dark channel and so on.These optical structures have important applications for the movement and trapping of tiny particles.This paper mainly introduces the following contents:The first chapter mainly introduces the significance of the subject research and the research results of domestic and foreign scholars.The second chapter mainly describes the mathematical description of the vector optical field,introduces two methods(active generation method and passive generation method)and applications of the generating vector optical field in the experiment,and mainly introduces the focusing properties of the vector optical field.The Richards-Wolf vector diffraction theory,4Pi focusing system model and various special focal field structures formed by the tightly focusing of vector optical field are described in detail.In the third chapter,the influence of DOE that modulates the incident optical field in the 4Pi focusing field is studied.Taking the Bessel-Gaussian optical field as an example,the 4Pi focusing fields of the radially polarized optical field modulated by several different DOE structures are analyzed by using the Richards-Wolf vector diffraction integral theory.The results show a multi-optical sphere structure with potential application value near the focal plane is obtained in the 4Pi focusing system.It is found that the number of optical spheres formed is related to the number of the ring of the DOE,while the transmission function of the DOE has no effect on it.And the number of optical spheres formed increases with the increase of the number of the ring of the DOE.On the basis of the third chapter,in the fourth chapter we study the 4Pi focusing properties of radial polarized vortex vector optical field,mainly study the influence of optical diffraction element(DOE),beam interception ratio(?)and topological charge(m)on the 4Pi focusing field.It is found that the optical cage structure and optical chain structure can be formed at the focal plane when the topological charge m=1.Increasing the beam interception ratio(?)will destroy the optical cage structure and optical chain structure,and the optical cage structure and optical chain structure can be reformed by adjusting the parameters of the DOE.When m>1,the optical chain structure is opened laterally,transforming into a dark channel structure.And the width of the dark channel increases with the increase of m.These research contents have important guiding value to realize the trapping and releasing of tiny particles.In the fifth chapter,we summarize the work of this paper and propose the prospect of the further research on the strong focusing properties of phase modulated vector optical field and the focusing properties in the 4Pi focusing system.