Phase-space density in the magneto-optical trap

We present an investigation of the cesium magneto-optical trap, with particular regard to the best combination of atomic density and temperature that can be produced. Conditions in the trap depend on four independent parameters: the detuning and intensity of the light, the gradient of the magnetic field, and the number of atoms trapped. We have varied all these parameters and measured the temperature and density distribution of the trapped cloud. Both the nonlinear variation with position of the restoring force and the reabsorption of photons scattered in the cloud limit the maximum density, and we present an empirical model that takes this into account. This in turn limits the density in phase space ρ (defined as the number of atoms in a box with sides of one thermal de Broglie wavelength). We have observed a maximum ρ=(1.5±0.5)×${10}^{\mathrm{-}5}$, with a spatial density of about 2×${10}^{11}$ atoms/${\mathrm{cm}}^3$.