Study On The Gradient Force Characteristics Of Vector Beams

The distribution of the polarization state of the vector beam is spatially variable,which makes the vector beam have great advantages in many fields.The optical gradient force is generated by the uneven intensity distribution of the optical field.Based on Richard-wolf diffraction theory,the gradient force distribution characteristics of cosh-Gaussian beams with the power–exponent–phase vortex are studied.Designed phase modulation focusing system,the manipulation of two different particles by a radially polarized Bessel-Gaussian beam is studied.The main contents of the thesis are as follows:1.The basic theories of vector beam,optical gradient force and optical tweezers are summarized,and the research status of optical gradient force and optical tweezers is briefly introduced.2.The Richard-wolf vector diffraction theory was introduced,and the detailed mathematical description of the vector beam was given.Then we derived the focusing expressions for some kinds of polarized beams,and the forces on particles with a size smaller than the wavelength in the optical field and the stability criterion of capture are introduced.3.The gradient force characteristics of cosh-Gaussian beams with the power–exponent–phase vortex is researched.We discussed the effects of power exponent,topological charge and decentered parameters on the gradient force distribution.The simulation results show that with the increase of power exponent,the gradient force trap will shrink gradually.With the increase of topological charge,the gradient force trap will gradually expand outward and rotate clockwise.With the increase of the decentered parameters,the distribution mode of the beam gradient force will gradually change from a circle to a square,and the maximum position of the gradient force will be transferred to the upper and lower ends.The conclusions provided a theoretical basis for manipulating particle capture and rotation,and have certain reference value for the research of optical tweezers system.4.A phase modulation focusing system is designed,and the focusing characteristics of a radially polarized Bessel-Gaussian beam passing through the system are studied,and the ability of the beam to manipulate bubbles and gold particles is analyzed.The results show that the designed phase modulation focusing system can successfully capture the bubbles and control the gold particles in the propagation direction.The proposed focusing system has the advantages of easy fabrication and low cost.The conclusions provided a new idea for studying the optical tweezers system.