Optical Dipole Forces On Atoms In Laguerre Gaussian Laser Fields

By means of the interaction between the light field and the dipole of the atom,the neutral atom can be guided,trapped and beam-split.At present,most of the studies on the optical dipole forces of atoms in the laser field are based on the Gaussian beam with a single spatial structure,while the interaction between the Laguerre-Gaussian beam with a complex spatial structure and atoms is relatively less studied.High-order Laguerre-Gaussian beams have unique advantages in laser manipulation and control of atoms due to their complex spatial structure.We mainly study the distribution of light intensity and optical potential of Laguerre Gaussian beams propagating at defined distance,as well as the radial,angular and propagating forces of three energy level atoms in the beams.In this thesis,the distribution of electric field in the far field of Laguerre Gaussian beam polarized along the x-direction is obtained by using the angular spectrum analysis method,and then the expression of optical dipole force of three-level atom is obtained by using Bloch equation.When the beam propagates farther and farther,the force range of the atom in the transverse plane perpendicular to the propagation axis becomes larger and the extreme value of the force becomes smaller and smaller.In Laguerre Gaussian beams with different radial mode numbers(LG0n),with the increase of the n,the peak value of the radial dipole force is larger and larger,and the phenomenon of positive and negative alternation appears.When the detuning is positive,the radial force mainly points to the central axis,and the angular dipole force is clockwise in the first and third quadrants,and counterclockwise in the second and fourth quadrants.When the detuning is negative,the radial force is mainly away from the central axis,and the angular dipole force is counter clockwise in the first and third quadrants,and clockwise in the second and fourth quadrants.In the distribution of radial force and angular dipole force in the transverse plane,the number of nodal circles,excluding the center of the circle,is 2n and n respectively.Among them,the angular dipole force is much smaller than the radial force.In Laguerre Gaussian beams with different angular mode numbers(LGm0),the transverse plane distribution of the radial optical dipole force on the atom is symmetric about the x and y axes.The number of nodal lines in the transverse plane distribution of the radial force is m,and there is also a nodal circle in the distribution,mainly because the electric field reaches its maximum at this position and the gradient is 0.When the detuning values are all positive,the radial force is first positive and then negative;when the detuning values are all negative,the radial force is first negative and then positive.The distribution of the angular couple force in the transverse plane is symmetrical about the center,and the number of nodal lines in the graph is twice that of m.