Mechanical Properties Of The Atom Interaction With The Laser Field

Abstract In laser cooling and trapping, the controllable force on the atom needs to be investigated. Usually, from a two-level atom, the multi-level atom can be simplified. The force acting on the atom can be analysed when the laser field interacts with the atom. In this thesis, a semiclassical model of the force on an atom is used to describe the motion of a two-level atom interacting with a standing-wave laser field. The velocity dependent force is derived through optical Bloch equations. It is shown that a negative detuning of the laser field from the atomic resonance would lead to nonzero light pressure forces and reduce velocities along the laser beam axis. When the intensity of the laser field is weak the velocity dependence of the average longitudinal force has the Doppler-shifted lorenztian resonance. At high intensities, there is a kink and change of direction of the light pressure force near the point of zero velocity. When the intensity of the laser field increases, the effects of the higher order harmonic light pressure forces become significant. It is seen that the behaviors of light pressure forces with even order are similar to the zero order force while that of odd order forces are opposite to the zero order one. Though the whole effects of the odd order and even order harmonic forces are almost destructive with each other for strong intensity, it is quite different compared to the case of weak intensity. For weak intensity, the higher order harmonic forces can be neglected.