Mapping of the Optical Frequency Comb to the Atom Velocity Comb

We present the experimental and theoretical study of the resonant excitation of rubidium and cesium atoms with fs pulse train in the conditions when the pulse repetition period is shorter than the atomic relaxation time. Velocity selective optical pumping of the ground state hyperfine levels and velocity comb-like excited state hyperfine level populations is demonstrated. Both effects are a direct consequence of the fs pulse train excitation considered in the frequency domain. A simple experimental apparatus was employed to develop a modified direct frequency comb spectroscopy which uses a fixed frequency comb for the 85,87Rb 5s 2S1/2 → 5s 2P1/2,3/2 and 133Cs 6s 2S1/2 → 6p 2P1/2,3/2 excitation, and a weak cw scanning probe laser at 780 and 852 nm for Rb and Cs ground levels population monitoring