We show that a single femtosecond optical frequency comb may be used toinduce two-photon transitions between molecular vibrational levels to formultracold molecules, e.g., KRb. The phase across an individual pulse in thepulse train is sinusoidally modulated with a carefully chosen modulationamplitude and frequency. Piecewise adiabatic population transfer is fulfilledto the final state by each pulse in the applied pulse train providing acontrolled population accumulation in the final state. Detuning the pulse traincarrier and modulation frequency from one-photon resonances changes the timescale of molecular dynamics but leads to the same complete population transferto the ultracold state. A standard optical frequency comb with no modulation isshown to induce similar dynamics leading to rovibrational cooling.
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