Study On The Properties Of The Circular Airy Vortex Beam And Its Application In Micro Manipulation

Optical manipulation technology has been widely used in physics,chemistry,biology,medicine and other scientific frontier fields since its invention owing to its advantages of non-contacting,non-invasive and high precision.Compared with the Bessel beam and the Gaussian beam,the circular Airy vortex beams(CAVB)has a unique self-focusing property,which makes it can produce a greater gradient force on the particle and improve the stability of capture,and can avoid obstacles to reach the target and push particles along parabolic trajectories.Therefore,Optical tweezers based on the CAVB is a new manipulation technology,which can greatly enrich and enhance the function of optical micro-manipulation,and hopefully solve the trapping dilemma of the traditional Gaussian beam.The key technical problems to be solved in the optical tweezers based on the CAVB are the generation,transmission,tightly focusing characteristics,optical force analysis and system implementation.In this paper,based on thorough study on the above key issues,a particle manipulation system is built to achieve the capture and rotation of silica particles.The thesis covers the following research works.Firstly,the generation of the CAVB is constructed based on computer generated holograms and spatial light modulators(SLM).The effects of various parameters of the CAVB on the self-focusing and self-bend characteristics are experimentally studied.The research contents including following two aspects:(1)The relation between light intensity distribution and focal depth with the parameters of CAVB,such as the decay factor,the scaling factor,the radius of the primary ring and the beam waist,is investigated in experiment and numerical simulation.(2)The phase singularity and self-healing behavior of CAVB is studied in experiment.The experimental results demonstrate that the focal intensity and the focal length of CAVB can be controlled by changing the incident beam parameters.Moreover,the CAVB maintains its optical vortex characteristics and has strong self-healing during propagation.Secondly,the influences of various parameters and polarizations of the CAVB on its tightly focusing characteristics are studied by numerical simulation.A method of generating super-long focal depth,super-strong longitudinal intensity or sub-wavelength focused spot at the focal plane is proposed.The research contents including following several aspects.The light field expressions for the focused fields with various polarization,such as linear polarization,circular polarization,radial polarization and azimuthal polarization are derived based on the Debye vector diffraction theory.Taking radially polarized CAVB as an example,the changes of intensity distribution,size of focal spot and the focus depth with different topological charges,decay factor,waist width,the radius of the primary circular and NA of the objective are investigated.Numerical results demonstrate that the radially polarized CAVB with super-long focal length,super-strong longitudinal intensity or sub-wavelength focused spot at the focal plane can be generated by properly choosing the parameters of incident light and high numerical aperture lens.Thirdly,the optical force and torque exerted on the Rayleigh particles by tightly focused CAVB in the far field are studied based on Rayleigh model.The longitudinal gradient force and transverse gradient force both increase with the increase of decay factor and scaling factor,and decrease with the increase of the radius of the first primary ring and topological charges.Moreover,the positions of the longitudinal stable equilibrium move toward the high numerical aperture lens when the scaling factor and the radius of the primary ring increase.The optical torque first increases and then decreases slightly after reaches a maximum with the increase of topological charges.In this paper,the expressions of the gradient force and scatter force exerted on the Rayleigh particles are drived,and the dependence of the trapping properties on the polarization,such as linear polarization,circular polarizations,radial polarization and azimuthal polarization are analyzed.Taking right circular polarization CAVB as an example,the changes of gradient force,scatter force and trapping position with the parameters of CAVB,such as topological charges,decay factor,waist width and the radius of the primary circular are investigated.The dependence of the optical orbital torque on the topological charges and the absorptivity of the particle is also studied.Lastly,according to the above research,an optical manipulation system based on the CAVB is constructed to capture and rotate the silica micro-particles.The system is also used to verify the characteristics of the self-focusing and parabolic transmission of the CAVB,and to study the relationship between the particle rotation speed and the topological charge.The rotational velocity of the micro-particles first increases and then decreases after reaches a maximum with the increase of topological charges,and the particles rotate in the opposite direction along the CAVB by changing the symbols of the topological charge.