Research On Tightly Focusing Characteristics Of Vector Light Field And Optical Polarization Topology

With the rapid development of photonics and laser technology,light field control has become an important method to expand laser applications,which is a research hotspot in the current optical field.The vector light field has spatially varying amplitude,phase and polarization distribution,and possesses the unique tight focus field characteristic.It is widely used in optical micromachining,optical micromanipulation,plasmon directional propagation,quantum optics and other optical fields.Combined the Richards-Wolf vectorical diffraction theory and the dipole antenna radiation theory,this paper studies tightly focusing characteristics of vector light field and the optical polarization topology.(1)Based on the Debye integral,we discuss the derivation process of the Richards-Wolf vectorical diffraction theory for calculating the focus of a high numerical aperture objective lens,and analysis the tight focus field distribution of some typical vector light fields.The focus field of radially polarized light has a longitudinal component whose intensity is much greater than that of the radial component,and the focus field of azimuthally polarized light only possesses a horizontally polarized electric field.(2)We study the focal field distribution reversely focusing the radiation field of the threedimensional polarized dipole antennae by a high NA objective lens or 4Pi focusing system.According to the time reversal method based on vectorial diffraction theory,by adjusting the dipole coefficients can change the relative amplitude and phase of different three-dimensional polarization dipole antennae.The 4Pi focusing system can greatly reduce the transverse stretching and obtain a three-dimensional focused spot with spherical structure.Compared with focusing by a single objective lens,the 4Pi focusing system strongly enhances the horizontal and vertical gradient force,which is of great significance in the fields of laser direct writing and optical probes.(3)According to the controllability of the polarization in the three-dimensional focus field,the specific polarization topology in the focus field can be generated by evenly placing the dipole antenna on the preset track near the focus.The sets of three-dimensional polarization dipole antennae carries the electric field data of the focus field of a unique Poincaré beam,which is generated from the q plate.The radiation field is coherently combined on the wavefront of a high NA objective lens.The 3/2 and 5/2 twisted optical polarization M(?)bius strips are formed in the focal field.The polarization topology of different circular paths surrounding the C-point some distortions undergo some deformation but always preserve M(?)bius strips with the same topology.The ability to customize polarization topologies may stimulate new effects and applications in nano-optics and complex beam engineering.