The Three Dimensional Manipulation Of Focal Fields For Complex Structure Optical Fields

With the development of laser physics,optics,as a basic natural science,plays an important role in scientific and technological progress and social development.The traditional scalar light field has a uniform distribution of its spatial polarization states.The manipulation of a scalar light field mainly involves the modulations of phase and amplitude.As the basic nature of the light,the vector optical fields with spatially inhomogeneous polarization states have been widely studied due to their unique spatial polarization distribution,the manipulation of polarization will inevitably generate many new physical phenomena in a vector optical field.The manipulation of the polarization state of the light field not only enriches the freedom of optical field manipulation,but also the emerging technologies and physical phenomena triggered by it are widely used in the fields of particle micromanipulation,quantum information processing,laser micromachining and optical information transmission.This paper studies the tight focusing phenomenon of the vector optical field,discusses the tight focusing property of the vector optical field in detail,and focuses on the analysis of the tight focusing property of the vector vortex optical field with fractional topological charges.Specifically,the research content of this paper is as follows:1.The background and current research status for the tight focusing of vector optical field are discussed,and the physical concepts of spin angular momentum(SAM)and orbital angular momentum(OAM)are reviewed.The two main methods of generating vector optical fields are explained: active method and passive method.We focused on the analysis of the method based on the common-path interference superposition of the 4f system to generate arbitrary vector optical fields,and used this method to experimentally generate the vector vortex optical field with integer or fractional topological charges(Vector Vortex Optical Field,VVOF).2.The for calculating the tightly focused focal field of the vector light field-the is described.Several formulas for the focal field intensity distribution of the vector light field are strictly derived according to the Richards-wolf vector diffraction theory.The focal field behavior of the fractional order vector vortex optical field(FO-VVOF)is analyzed with comparison to tht of the integer order vector vortex optical field.The experiment indicates that FO-VVOF have odd or even focal spots in the focal region,depending on the value of the fractional topological charges of the incident field.When the polarization topological charge m and the phase topological charge n are equal m = n,the focal field bright spot appears in the center of the focal field.The analysis of the polarization state of the initial optical field shows that FO-VVOF can be regarded as the coherent superposition of the two different vorteices with orthogonal circularly polarized components.3.The Poynting vector distribution(energy flow distribution)and angular momentum distribution of the focal field when the FO-VVOF with locally linear polarization is tightly focused are studied.The results indicates that a circular polarization component appears in the cross section of the light field when the initial optical field is tightly focused by a high numerical aperture lens.The appearance of circular polarization suggests that the tightly focused optical field will undergo a linear polarization-to-circular polarization conversion,generating the spin angular momentum(i.e.SAM).The appearance of circular polarization results in the total angular momentum redistribution of the light field,leading to the longitudinal orbital angular momentum component appearance in the focus field.The internal physical mechanism of linear polarizationcircular polarization conversion,and the physical principle of SAM and OAM conversions on the cross-section of the focal field are discussed in detail.