Nonlinear Light Field–Control And Application Of Airy Autofocusing Beam

In the past ten years,autofocusing beams have made great breakthroughs in theoretical basis and experimental application,attracting extensive attention and interest of scientists.Autofocusing beams originated from radially symmetric annular Airy beams,and then a series of suddenly autofocusing beams were constructed one after another.The characteristic of autofocusing beam is that its peak intensity keep unchanged in a propagation distance.When approaching a specific focus position,the beam will suddenly focus at a point,and the peak intensity of the beam are greatly enhanced a lot.Due to this special property,autofocusing beams have been widely studied and applied in many fields,such as particle manipulation,light bullet generation and so on.However,so far,the researches on autofocusing beams mainly focus on the improvement of autofocusing beams and their propagation properties.There is a lack of quantitative and systematic research and exploration on the trapping performance such as optical trapping force and trapping stiffness in particle manipulation,greatly limiting the popularization and applications of autofocusing beams.Due to this,this thesis takes airy autofocusing beam as an example to comprehensively discuss and analyze the propagation dynamic characteristics of autofocusing beams and their trapping performance in the application of optical tweezers,including proposing the relevant improving methods.The main contents are as followed:(1).By superimposing a plurality of two-dimensional Airy beams,a two-dimensional superimposed airy autofocusing beam is formed;Their propagation dynamic characteristics in free space and disordered media are studied theoretically and experimentally,and their transmission stability,dynamic power flow and trapping force characteristics are studied from different viewpoints.The results show that,the two-dimensional superimposed Airy beams have superior stability.Their autofocusing propagation and trapping performance can be controlled by changing the number of superimposed beams,truncation factor,scale factor,initial position and the angle between the two wings of the two-dimensional Airy beam;The analysis on the evolution of power flow and dynamical trapping force further demonstrate that the two-dimensional Airy superimposed beam repeats multiple autofocusing propagation processes,resulting in a series of autofocusing and stable trapping positions in the propagation;Compared with the traditional autofocusing beam circular Airy beam and one-dimensional superimposed Airy beam,the two-dimensional superimposed Airy beam shows better optical trapping performance,which is also confirmed by the experiment of measuring the optical trap stiffness by power spectrum method.(2).The vortex phase is introduced on the two-dimensional superimposed Airy autofocusing beam to form a two-dimensional superimposed Airy vortex beam;The autofocusing propagation dynamics and trapping force characteristics of two-dimensional superimposed airy vortex beams are studied theoretically.The related power flow characteristics and the evolution of trapping force are also analyzed.It is found that the autofocusing peak intensity,trapping force and trapping stability of two-dimensional superimposed airy vortex beams can be improved by increasing the number of superimposed Airy beams;With the increase of topological charge,the peak intensity of two-dimensional superimposed airy vortex beam first decreases and then increases;The autofocusing ability of the beam at the focus position decreases gradually,but the autofocusing ability before the focus will increase,and the position with the best autofocusing performance will move forward with the increase of topological charge.In addition,due to the orbital angular momentum,the capture position of the two-dimensional superimposed airy vortex beam can rotate and is controlled by the topological charge.The larger topological charge can help the two-dimensional superimposed airy vortex beam rotate the captured particles faster.In this case,the trapping stiffness and gradient force of the two-dimensional superimposed Airy vortex beam are relatively small,but it can capture larger objects in the form of dark light field.(3).By adjusting the circular Airy beam,a specially modulated autofocusing beam: Bessel modulated autofocusing beam is designed and demonstrated.Theoretical and experimental results show that compared with the unmodulated autofocusing beam,the performance and capture ability of this modulated beam have been greatly improved,showing shorter focal length,stronger peak intensity and optical trapping force.Furthermore,by comparing the capture of polystyrene spheres and red blood cells,it is found that Bessel modulated beam has stronger trapping force due to its unique intensity,showing the potential of low photodamage with optical tweezers and implying great application prospects in biomedicine research.