Bose-Einstein condensation of a system of two-level atoms in resonant interaction with a single-running-wave-mode laser field

Abstract

In this thesis, we study the influence of a single-running-wave-mode laser field to the critical temperature T[] of Bose-Einstein condensation(BEC) of a system of two-level bosonic atoms. Using a simple model, we obtain the dispersion relation for these atoms in a laser field within the approximation that the photon number N is much larger than the atom number N[]. Thus starting from this relation, we derive an integral equation about the critical temperature of BEC. Solving this equation numerically, we obtain T[] for different parameter values. Detailed analyses about 3 special cases are made. We found that for strong laser field, T[] does not change appreciably. The other limit of weak laser field is also analyzed, but it actually must not be too weak since we have assumed N >> N[]. If a special condition on the laser strength is satisfied, T[] for BEC exhibits a local minimum. At this special intensity of the laser field, the BEC is expected to be of a new kind, with more than one state near the spectroscopic minimum involved in BEC for 0<T<T[]. We also evaluated the possible values of the two dimensionless parameters for a real system, viz., dilute-sodium-gas studied in an actual BEC experiment together with a visible laser light, and found that it is very difficult to satisfy this special condition unless the atomic density is reduced to ~1 cm⁻³, but the T[] will be reduced to ~ 10⁻¹⁵ K. However, by using untypical values for some of the physical parameters, we find that it should be possible to realize this very interesting special case.