Focused Radiation Force Of Structured Beam And Its Applications

A strongly focused laser beam produces a three-dimensional potential trap that captures particles.This three-dimensional potential well is called the optical tweezers.It not only can control small objects without contact,but also has strong compatibility.It can couple different structural beams into the optical tweezers system to obtain different phenomenon.For example,the Bessel beam can simultaneously capture multiple particles in multiple planes in an optical tweezers system;hollow beams can reduce energy thermal damage while increasing axial trapping force;radial polarized beam ratios and other polarization states can easily capture special particles;vortex optical tweezers an use their orbital angular momentum to drive particle rotation;In this dissertation,study the focusing characteristics of different structural beams and the radiation force on the particles.The main work includes:1.Based on the Debye integral theory,the linearly polarized of circular partially coherent Gaussian beam is studied by the principle of large numerical aperture tight focusing.The numerical aperture and the coherence length of the beam are studied.The results show that the numerical aperture and coherence length have obvious influence on the axial radiation force.The numerical aperture variation causes the focused spot to become smaller and the gradient force to become larger.And the reduction of the coherence length will cause the focused spot to generate a uniform needle beam in the axial direction.The uniformity of the needle beam in the axial direction results in a weak axial gradient distribution,which is not conducive to better capturing of particles.2.Based on Richards-Wolf's vector diffraction theory and Rayleigh scattering theory,the variation of the light field and radiation force of the radially polarized circular partially coherent Gaussian beam after tight focusing is numerically simulated.The study found that in the process of large numerical aperture focusing,stable three-dimensional capture of polystyrene beads can be achieved.In addition,it has been found that by selecting a suitable coherence length,needles beam and dark channels with wide application significance are obtained.Through the simulation of optical capture by needle beams and dark channels,it is found that needle beam anddark channels are theoretically less likely to optically capture particles.3.The vortex beam is captured experimentally to capture the microbubbles,and the effects of different topological charges and power on the lateral trapping force are compared.The experimental results show that the smaller the topological charges,the larger the lateral stiffness coefficient,and the vortex beam with low topological charges has lateral trapping force.