Figure 24.2 — Two-level atom and optical molasses Figure 24.2 — Two-level atom and optical molasses. (a) Energy levels of a two-level atomic system showing the detuning of an incident laser beam from resonance, δ = ω − ω0. (b) Configuration of laser beams for a one-dimensional optical molasses, i.e., a pair of counter-propagating beams detuned by δ from the atomic resonance. (c) Radiation force for a one-dimensional optical molasses as a function of atomic velocity. The linear region near v = 0 corresponds to viscous damping.