See-saw Doppler cooling of three-level atoms by coherent pulse trains*

We explore the feasibility of decelerating and Doppler cooling an ensemble of three-level $\Lambda$-type atoms by a coherent train of ultrashort laser pulses. In the frequency domain such trains form frequency combs. We show that driving atoms by frequency combs that do not satisfy the two-photon Raman resonance condition results in a persistent radiative force. We also propose a see-saw scheme of cooling multilevel atoms. In these scheme the teeth of the frequency comb are periodically moved in and out of resonance for the allowed transitions. The see-saw cooling may be practically attained by switching carrier-envelope phase between predefined values. We carry out numerical calculations of optimal train parameters, radiative force and time evolution of the velocity distribution