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Journal of Physics B Atomic Molecular and Optical Physics

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

Marco Polo Moreno de Souza, C. A. C. Bosco, L. H. Acioli, D. Felinto, S. S. Vianna

Published Feb 16, 2010• 4 citations
Publisher

Abstract

We report on a detailed investigation of the coupling between a femtosecond-laser frequency comb and a cw diode laser interacting with an atomic medium of variable density. The comb is printed on a Doppler-broadened atomic transition and the frequency-dependent transmission of the cw laser is monitored as it is scanned over the inhomogenously broadened absorption profile. The printing process and its probing are analysed, experimentally and theoretically, as a function of both laser intensities and the atomic density. The results reveal the importance of optical pumping and power broadening by both lasers, allowing us to determine various regimes of competition between them.

DOI
10.1088/0953-4075/43/5/055001

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We investigated the coherence accumulation in Rb atoms excited by a train of femtosecond pulses. The coherence accumulation results in the velocity selective optical pumping of Rb hyperfine levels, observed by a cw probe laser. The effects of the pulse train excitation on the cw probe laser transmission were investigated, depending on the probe laser power. We observed the probe laser absorption increase in the strong probe case, followed by the reduction of the modulations in the probe laser absorption. Results show that accumulation of population and coherence can be effectively reduced and eventually destroyed by increasing the cw laser intensity. A strong cw laser can therefore serve as a switch from the pulse-train to pulse-by-pulse type of interaction of Rb atoms with the fs laser. We developed a density-matrix based theoretical model of the eight-level Rb atoms interacting with the fs and cw laser fields, and present agreement with the experimental results.
We use a 1 GHz femtosecond laser as a tool to perform coherent spectroscopy in an atomic vapor. The action of the ultrashort pulse train over the various velocity groups or over a selective group of rubidium atoms is probed by a diode laser using velocity-selective or repetition rate spectroscopies. In particular, we show that the 1 GHz frequency separation of the modes in the frequency comb allows distinguishing of the different hyperfine levels within the Doppler broadened profile. The data are in good agreement with numerical and analytical results.
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