Two-photon and EIT-assisted Doppler cooling in a three-level cascade system

Laser cooling processes are theoretically investigated for a cascade scheme of atomic levels where the upper state decays more slowly than the intermediate one. A laser coupling to the upper transition modifies the scattering cross section, such that its action results in temperatures lower than those reached by Doppler cooling on the lower levels. We identify two regimes: when multiphoton processes due to the upper laser are relevant, the formation of an atomic coherence between ground and upper state affects the cooling dynamics, and the final temperature is controlled by the second laser parameters. When the intermediate state is only virtually excited, the dynamics are dominated by the two-photon process and the final temperature is determined by the spontaneous decay rate of the upper state