Optical Manipulation Of A Rayleigh Particle Using A Vector Bessel Beam

Single beam optical traps, nowadays known as optical tweezers, used its mechanical effect of light trap tiny particles effectively. Because of the non-contact, low damaged advantages,it has been widely used as an powerful tool to investigate the neutral atoms, etc, used in various fields including biology, chemistry, medicine, physics and micro fluidic optics and so on.At the same time,it also put forward new requirements and challenges. Bessel beam can make up the deficiency of Gauss beam in optical control, and realize some new functions.In this thesis, the mechanical effect of the Bessel beam on the Rayleigh particles is studied by considering the non diffraction, self-healing or self-rebuild and polarization properties of the Bessel beam. The main research work a of this thesis are as follows:Firstly, we will derive the analytical formulas of EM fields for a vector high-order Bessel beam according to angular spectrum representation.Based on this, we derive the intensity and Poynting vector of the vector Bessel beam, and analyze their characteristics. According the numerical study on the intensity Poynting vector of the vector Bessel beam,we discover that the polarization of Bessel beam beam affects the position of the maximum intensity as well as the range of energy flow by corresponding incident beam.Secondly,we will derive the optical force exerted on a Rayleigh particle by a vector highorder Bessel beam using the Rayleigh model,taking polystyrene spherical Rayleigh particles as examples,obtain the radial, azimuthal, as well as longitudinal forces.In the process of the derivation of the formula,we discuss the characteristics of the optical force under different conditions,with emphasis on the effect of the Bessel function order l,non-paraxiality and polarizations including linear polarizations, circular polarizations, radial polarizations, azimuthal polarizations and non-polarizations,and analyze the number of equilibrium point.The results show that the polarization state of the Bessel beam influence the equilibrium position of trapped particles in different directions.Thirdly, we discuss the torque of the vector Bessel beam on the Rayleigh particles by a vector high-order Bessel beam, which include the extrinsic torque and intrinsic torque.Similarly,we will discuss the influence of the Bessel function order l, the polarizations and non-paraxiality on the extrinsic torque, the intrinsic torque and the resultant torque.The numerical analysis shows that the polarization state of the beam impact the magnitude and the positive and negative of the torque.