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Physical Review A

Numerical analysis of a Cs magneto-optical trap

Jin Woo Jun, Ho Seong Lee

Published May 16, 2000• 2 citations
Publisher

Abstract

Using the recently developed kinetic theory we calculate the intensity dependence and the detuning dependence of the Cs temperature and the Cs cloud radius in a magneto-optical trap (MOT). We find that the tendencies and the absolute values are in reasonable agreement with the experimental data of Drewsen et al. [Appl. Phys. B: Lasers Opt. 59, 283 (1994)] and that our kinetic theory deserves a quantitative and consistent theory of MOT's.

DOI
10.1103/physreva.61.065401

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A cloud of ultracold atoms confined in a magneto-optical trap (MOT) has a temperature greater than that of a low-density vapour in the same light field. It has been observed (Drewsen M. et al., Appl. Phys. B , 59 (1994) 283) that this temperature excess is proportional to the cube root of the total number of trapped atoms ( N 1/3 ). We present an explanation for this effect in terms of the scattering which arises when photons spontaneously emitted by atoms have an appreciable probability of being reabsorbed within the cloud. This hypothesis has been tested by time-of-flight measurements of the temperature of clouds of atoms released from a MOT into 1-dimensional and 3-dimensional optical molasses in the σ + -σ - and lin ⊥ lin configuration.
We generalize the kinetic theory of the magneto-optical trap (MOT) to investigate the finite-linewidth effect of cooling lasers. Our results confirm that the polarization-gradient cooling mechanism in the low-velocity domain of the MOT originates from a two-photon process and that the Doppler cooling mechanism in the high-velocity domain stems from a one-photon process. We find that, when we increase the linewidth of the cooling lasers, the cooling temperature increases monotonically and the atomic cloud radius initially decreases quadratically and later increases.