Optical spectroscopy of trapped neutral atoms

In the last two decades the atomic physics community acquired a great capability of controlling the atomic motion. Since the proposal of Hansch and Schawlow to utilise the radiation pressure to optically cool atoms, much effort has been done to develop laser cooling techniques. The first experiments were unidimensional, with one or more lasers used to cool the longitudinal velocity distribution of an atomic beam. In 1985 a three-dimensional configuration made by mutually orthogonal laser beams tuned to the red side of the atomic resonance was used by Chu et al. to produce optical molasses. The density of cold atoms collected in this way is quite low and the cold atomic sample is easily destroyed by any interaction. This problem is overcome in a trap where atoms are simultaneously cooled and trapped by a combination of laser beams and magnetic fields. The first magneto-optical trap (MOT) loaded from an atomic beam was reported by Raab et al. while an important step was achieved by loading a trap directly in a vapor cell. In a vapor cell MOT atoms are captured from the low-velocity tail of the Maxwellian distribution so heavy atoms can be efficiently trapped in this way, while light atoms are more likely captured from atomic beams witt precooling techniques