Manipulation And Application Of Optical Field Energy Flow

Energy flow is an important kinetic property of the optical fields,which plays a very important role in the interaction between light and matter and has been widely used in scientific and engineering fields such as optical imaging,near-field optics,nonlinear optics,optical trapping and particle manipulation.Therefore,the study of the modulation,transport and application of vectorial optical field energy flow with a richer spatial topological distribution is a very important research direction in the field of optics and nanophotonics,which has attracted extensive attention.In this paper,we take the manipulation and application of energy flow as an entry point to modulate the vector optical field by optical degrees of freedom such as amplitude,polarization state,and phase,and investigate the tightfocusing characteristics of different input beams after passing through a high numerical aperture objective,and also discuss the spin and orbital motion of particles in the tightfocusing optical field.In addition,the energy flow reveals the propagation direction of the optical energy,which can be used to control the transport of the absorbing particles along specific paths,contributing to the optical trapping and providing a possible pathway for the optical identification and separation of spherical particles.The main research of this thesis can be summarized as follows:1.Based on the Richard-Wolf vectorial diffraction theory,the expressions for the electromagnetic field of a spatially varying column vector beam on a high-order Poincarésphere after tight focusing by a high numerical aperture objective are derived in detail,and the integral expressions for a typical Laguerre Gaussian beam are derived.2.The focusing characteristics on the focal plane of the tightly focused system are studied.Based on the Richards-Wolf vectorial diffraction integral,the effects of optical degrees of freedom such as polarization,ellipticity,handedness and polarization-ellipse orientation on the electric field distribution,magnetic field distribution,spin energy flow distribution,orbital energy flow distribution and energy flow distribution in the tightly focused field are discussed from the perspective of Poincaré sphere.The calculation results show that the ellipsometric angle and the rotation direction affect the magnitude and direction of the transverse energy flow respectively,but have little effect on the longitudinal energy flow,while the polarization-ellipsometric orientation has no effect on the transverse energy flow and the longitudinal energy flow.Different from the traditional optical vortex modulation,the energy flow on the focal plane will no longer be symmetrical after the annular spiral phase plate modulation.Instead,it is the distribution of polygons,and the number of edges and topological charges of polygons maintain a one-to-one correspondence.3.Based on the dipole approximation theory,the distribution of the optical force generated by the tightly focused beam on the particles under different electromagnetic fields is studied.Based on the force model of nanoparticles in tightly focused Laguerre-Gaussian beams,the identification and capture of nanoparticles are realized by controlling the angular polarization index.A method for identifying and separating nanoparticles is theoretically proved,and the spin-orbit motion of particles is studied.