INVESTIGATION OF SUB-DOPPLER COOLING EFFECTS IN A CESIUM MAGNETOOPTICAL TRAP

We present an investigation of sub-Doppler effects in a cesium magneto -optical trap. First, a simple one-dimensional theoretical model of th e trap is developed for a J(g) = 1 --> J(e) = 2 transition. This model predicts the size of the trapped atom cloud and temperature as a func tion of laser intensity and detuning. In the limit of small magnetic f ield gradients, the trap temperature is found to be equal to the molas ses temperature and a minimum size for the trap is calculated. We then describe several experiments performed in a three-dimensional cesium trap to measure the trap parameters, spring constant, friction coeffic ient, temperature and density. Whilst the temperature of the trapped a toms is found to be equal to the molasses temperature, in agreement wi th theory, the trap spring constant is found to be two orders of magni tude smaller than the one-dimensional prediction, a value close to tha t predicted by Doppler models. The maximum density is found to be on t he order of 10(12) atoms/cm3 or one atom per optical wavelength on ave rage. When the number of trapped atoms becomes large, the temperature begins to increase dramatically. This excess temperature depends in a very simple way on the atom number, laser intensity and detuning, sugg esting that its origin lies in multiple photon scattering within the t rap.