Dynamical behaviour of the temperature in Cs optical molasses

We measured the temperature of Cs atoms in an optical molasses after a sudden intensity reduction of the cooling beams. The temperature exhibits an interesting temporal behaviour in that the decay follows a series of exponential curves which can include a few damped oscillations. We present the results of a one-dimensional model which reproduces the features observed experimentally. The complex decay of the temperature is understood as a result of frictional forces in the molasses and collective oscillatory motion of the atoms. This is interpreted as showing a spatial localization of the atoms in the optical quasi-lattice formed in a six-beam molasses.