Dynamics of atoms in a femtosecond optical dipole trap

Abstract

The semiclassical theory of atomic dynamics in a three-dimensional pulsed optical dipole trap formed by superimposed trains of short laser pulses (down to a few fs duration), which is based on a stochastic formulation for the dynamics of an open quantum system, is considered in detail. It covers all key features of the atomic dynamics in the trap, including the dipole-dipole interaction (DDI) between trapped atoms due to the exchange of virtual photons between the atoms. Analytical solutions are obtained for the relaxation and laser Liouvillians, which describe the dissipation and laser excitation in the system, respectively. The probabilities of single-atom and two-atom escapes from the trap are analyzed. As an example, the theory is applied to computer simulation of Rb atoms preliminarily cooled in a magneto-optical trap that are trapped in a femtosecond optical dipole trap (pulse duration 100 fs). Our simulations prove that such a trap effectively confines atoms at the pump laser power in the range from a few mW to several kW. It is also shown that a near-resonant DDI, through which atoms that are closely spaced in the micropotential wells interact with each other, can be significantly increased by illuminating the atoms with a near-resonant probe laser beam. By varying both the parameters of the trap and the intensity of the probe laser field, the role of the DDI in the atomic dynamics in the trap and its influence on the single-atom and two-atom escape rates are clarified in detail.