Detection of excited level population transfer in an MOT through the measurement of trapped atom number

We study the rubidium magneto-optical trap (MOT) population changes induced by a laser beam interacting with the trapped atoms and resonant with different transitions from both the ground and the excited trap levels. Laser excitation outside the cooling scheme induces losses in the MOT population, while the laser increases the trap population when tuned to transitions linked to the trapping cycle. The experiment is performed with a small number of trapped atoms (100 to 10 000). A discussion of our ability in manipulating the atomic population of different hyperfine states is reported