Coupling between cw lasers and a frequency comb in dense atomic samples - Conclusions

1. Introduction
2. Experiment
4. Conclusions

In this paper we have presented new results on the coupling between femtosecond-laser frequency combs and a cw diode laser. This coupling process was experimentally investigated when the cw-laser frequency is scanned over the inhomogeneously broadened D2 resonance line of 87Rb, and the printing of the fs-laser frequency comb in the Doppler profile was studied as a function of the atomic density and laser intensities. We have used the simplest possible model, one that takes into account the interaction of the two laserswith an ensemble of four-level atoms, to explain the experimental results. Our analysis reveals the roles of optical pumping and power broadening in the establishment of the various regimes of competition between the two lasers, depending on their relative intensities and on the nature, if open or closed, of the atomic transition excited by the cw diode laser. We have also shown that the various velocity groups of atoms are sensitive to the femtosecond-laser frequency comb, even for high cw laser powers, but the Stark shift of the atomic transitions by the cw laser displaces the printing of the comb teeth in the Doppler profile. This result leads to the reinterpretation, with respect to [13], of the blurring of the printed comb as a result of power broadening on the atomic transition by the cw laser. Further, we have shown that open or closed transitions have considerably different behaviours as the cw power is increased, which explains well the distortions observed in the comb printed in the Doppler profile as the atomic density is changed.

This work was supported by CNPq, FACEPE and CAPES (Brazilian Agencies).


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