In 1985, at first time, it was possible to get cool atoms using laser light. With this mechanism they got a gas of atoms (optical molasses) at temperature of 100 ?K. This facts was according with a theoretical model for atoms of two levels, which get cool by Doppler effect. The experiment confirmed the lower temperature achieved by this mechanism (Doppler Limit). In similar experiments, in 1988, the optical molasses shown lower temperatures that Doppler limit; on the order of 10 ?K. It needed a new theoretical model in order to explain these news results. The New model, presented by S. Chu & C. Cohen-Tannoudji, and their colleagues, considers: the atomic sublevels (Zeeman sublevel), the light shift, polarization gradient and optical pumping. The combination of these effects does that atom’s energy depends of his position in the molasses. When the atoms travel through the molasses, they lose more and more energy, and then the gas gets cool. This new mechanism for laser cooling is named “Sisyphus Cooling”.