Mechanical Effect in the Two-Dimensional Laser - Interaction

In this thesis, we investigate theoretically the light pressure force and atomic motion for an atom interacting with a two-dimensional laser field. We demonstrate that the two-dimensional light pressure force and atomic motion can be substantially distinct from the descriptions of a simpler one-dimensional theory. We have identified new mechanisms and features of 2-d atomic motion. The results not only unveil to us a clearer picture of complex atomic motion in a 2-d laser field, but may also be crucial in understanding many anomalous observations in optical molasses and trapping experiments. When an atom moves in a 2-d standing wave formed by two orthogonal optical standing wave fields, we show there can be an anisotropic cooling-heating force which may cool the atoms along one field axis while heating them along the perpendicular axis. The force is identified as a spontaneous vortex force associated with the local traveling wave character of the two-dimensional field. We show this anomalous force may be interpreted in terms of the interplay between the vortical momentum flow of the light field and a motion-induced population transfer between the ground and excited atomic states. For a multilevel atom in a 2-d sigma _{+} - sigma_ {-} laser field with the presence of a transverse dc magnetic field, we show there can be a velocity -dependent vortical force which may compel the atoms to swirl circularly around velocity vortices. In some limits, this vortical force can be approximated as, Q_ {eff} vec v times vec B (where Q_{rm eff} is effective "charge"), which may be interpreted as a 'Lorentz' force on the atom 'charged' by the laser -atom interaction. When the atom interacts with a 2-d laser field, the atomic momentum distribution may exhibit symmetry about the x- and y-axis, permutation symmetry between two axes and a 90^circ-rotation symmetry provided that the laser intensities along two axes are tuned exactly the same. We show symmetries may be broken by the anisotropic force and velocity vortical force. To solve the light pressure force and atomic motion, we develop an efficient numerical technique which empowers us to investigate complex dependence on the velocities, intensities and phases.