Study On The Propagation And Applications Of Vector Beam In Strongly Nonlocal Nonlinear Media

With the development of laser technology,more and more researcher realize that the rich information carried by light can be used as a mean of detecting and sensing the material world.In order to fully explore the significance of photons as information carriers,it is necessary to deeply analyze the dynamic information of the beam field.Vector beam plays an important role in the spatial evolution of beam field and the interaction between beam and medium because of its special property of unique distribution of polarization state in space compared with the ordinary scalar beam field.At present,there are many applications in optical trapping,optical micromanipulation and optical micromachining.With the development of the fabrication technology of various micro-nano structure materials,the new effect of interaction between material and beam has been discovered.In this thesis,the propagation characteristics and applications of vector beam in strongly nonlocal nonlinear media are studied.Firstly,the dynamic behavior of the beam field in the strong non-local nonlinear medium are investigated,and the methods of generating vector beam field,including the 4F-system method.And a vector beam field with radial-variant or azimuthal-variant polarization state is experimentally generated.In this thesis,the mathematical expression based on Stokes vector formula of the beam intensity,amplitude and polarization state of the vector beam field is introduced,and the theoretical model for the propagation of a vector beam field in a strongly nonlocal nonlinear medium is provided.Secondly,based on Rayleigh-Sommerfeld diffraction integration and the variable transformation technique,the analytic solutions of vector beam field in strongly nonlocal nonlinear medium are obtained by using the corresponding relation between the analytic solution of vector beam field in free space and in strongly nonlocal nonlinear medium.The dynamical properties of the radial-variant vector beams(RV-VBs)in a strongly nonlocal nonlinear(SNN)media are theoretically investigated.Based on the moments method,the analytical expression for the root-mean-square(RMS)of the RV-VBs propagating in a SNN media is derived.The critical powers that keep the RMS beam widths invariant during propagation in a SNN medium are discussed.The RMS beam width tends to evolve periodically when the initial power does not equal to the critical power.The evolution of the structured statesof polarizations(SoPs)of RV-VBs in a SNN media is obtained by numerical simulation.The numerical calculations indicate that the conversion between linear and circular polarizations occurs especially in the beam center during propagation in a SNN medium.Furthermore,the positions of the peak intensities of different polarizations can be controlled by the input powers.The underlying physics for the linear-circular polarization conversion in a RV-VBs during propagation in a SNN medium are discussed in detail.The evolution of a fractional vector vortex beam with a spiral phase and azimuthally-variant polarization in a strongly nonlocal nonlinear(SNN)medium is demonstrated.The dynamics of interplay between the singular points of polarization and vortex during propagation in the SNN medium lead to novel phenomena.When the topological charge number of the polarization is equal to that of the vortex,the singular point in the beam center is annihilated and the energy can accumulate in the beam center due to the self-focus effect.Finally,based on the local circular polarization state of the RV-VBs changing with the input power and propagation distance in strongly nonlocal nonlinear medium,a divice that can generate and switch circular polarized beam is proposed.The device can generate left-handed,right-handed or left-right mixed circular polarized beam in a fixed position by controlling the initial power of the vector light field or the thickness of the SNN medium.This thesis also presents a bifocal imaging system based on the bifocal characteristics of the vector light field with a novel polarized radial variation.By calculating the influence factors of the dual-focus distance,the bifocal system with controllable bifocal spacing can be realized.