Abstract

The process of collisional trap loss in magneto-optically trapped ⁷Li shows a rich dependence on the depth of the trapping potential, E_T. When the trap is shallow enough to allow the escape of atoms with kinetic energy equal to one-half the fine-structure splitting, ΔE_fs, fine-structure changing collisions [FS] dominate the collisional trap loss rate. However when the trap is deeper than $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\Delta E_{\text{FS}}$, only the radiative escape mechanism [RE] contributes to trap loss. In this regime, Julienne and Vigué predicted that the collisional loss rate will depend on E_T as ~E_T^-17/6.¹ We have measured the collisional loss rate, β, of ⁷Li from a beam-loaded magneto-optical trap.² The circles in Fig. 1 show the data for four different trap laser detunings, Δ, and a range of trap laser intensities, 1. The solid line in Fig. 1 is the result of a semi-classical, optical Bloch equation calculation of the RE trap loss rate³ using as input E_T, calculated from a truly three-dimensional model.⁴ The trap depth model predicts that E_T is anisotropic. The dashed line in Fig. 1 shows the intensity at which the model predicts $E_T>\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\Delta E_{\text{FS}}$ in all directions, for each detuning. The theory predicts the magnitude of the RE trap loss rate accurately near the point at which the fine structure mechanism turns off, where the trap depth is well known. However at larger detunings and intensities the calculations deviate from the measured values. This suggests that the trap depth model overestimates E, at higher intensities and detunings, or that the trap depth dependence of the RE loss rate deviates from E_T^-17/6.

© 1994 Optical Society of America