0 10 20 30 40 t 0 0.2 0.4 0.6 0.8 1 population FIG. 7: Population transfer in the three-level λ -system, achieved using an optical frequency comb as in Eq.(3) with the carrier frequency of the electric field detuned off resonance with the ω 32 in the λ -system. The detuning δ is 3 / 2 ω 31 . Bold black, bold red, and bold green lines show population of the Feshbach state, the excited electronic state and the final, ultracold state for the Ω$_{R}$=1.26 THz, ( 10 12 W/cm $^{2}$), thin lines show respective populations for Ω$_{R}$ =12.55 THz, ( 10 14 W/cm $^{2}$). Pulse train period is T = 6400 τ = 0 . 02 ns . to full population transfer is based on the excitation of the two-photon Raman resonances. For both, the resonant and detuned Raman transition to happen, the radio frequency f$_{r}$ characterizing the optical frequency comb has to be such that, multiplied by integers n and m, it forms the modes at the pump and Stokes frequencies, whose difference, nf$_{r}$ − mf$_{r}$ , is in resonance with the two-photon Raman transition frequency. In the case of sinusoidally modulated optical frequency comb, the Raman transitions are stimulated by the carrier and the modulation frequencies. A special attention has to be paid to adjusting the modulation amplitude (the index of the Bessel function, describing the optical frequency comb), based on the comparison of the power spectrum with the energy levels in a molecular system to be cooled. Compared to [7, 8], implementation of a single optical frequency comb rather than two combs is more robust for experimental realization. A single femtosecond optical frequency comb, with no modulation or sinusoidally phase modulated, induces coherent adiabatic accumulation of population in the ground state. Similar to the mechanism behind the two frequency combs approach, a small fraction of population is transferred by each pulse in the pulse train due to its very small pulse area. When sinusoidal phase modulation 12