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Theory of Dicke narrowing in coherent population trapping

O. Firstenberg·M. Shuker·A. Ben-Kish·D. R. Fredkin·N. Davidson·A. Ron
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Abstract

The Doppler effect is one of the dominant broadening mechanisms in thermal vapor spectroscopy. For two-photon transitions one would naively expect the Doppler effect to cause a residual broadening, proportional to the wave-vector difference. In coherent population trapping (CPT), which is a narrow-band phenomenon, such broadening was not observed experimentally. This has been commonly attributed to frequent velocity-changing collisions, known to narrow Doppler-broadened one-photon absorption lines (Dicke narrowing). Here we show theoretically that such a narrowing mechanism indeed exists for CPT resonances. The narrowing factor is the ratio between the atom's mean free path and the wavelength associated with the wave-vector difference of the two radiation fields. A possible experiment to verify the theory is suggested.

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O. Firstenberg, M. Shuker, A. Ben-Kish, D. R. Fredkin, N. Davidson, A. Ron. 2007-01-15. Theory of Dicke narrowing in coherent population trapping. https://doi.org/10.1103/physreva.76.013818

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