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 two-photon 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.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 two-photon 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.

arXiv:quant-ph/0701008Physical Review AJul 19, 200739 citations

Power broadening of Doppler-free two- and three-photon resonances

Martin F. H. Schuurmans

Physics Letters AOct 1, 19775 citations

Isotopic shift, pressure shift, and pressure broadening of the 7d′ states of neon using Doppler-free two-photon absorption spectroscopy

M. M. Salour

Doppler-free two-photon transitions between the $3s$ , $J=2$ metastable state and the subconfiguration $7{d}^{\ensuremath{'}}$ of neon are studied with a pulsed-dye-laser oscillator-amplifier system which was synchronized with a chopped rf discharge in neon vapor. The isotopic shifts for these transitions are measured, and based on these measurements we have made a systematic study of Ne-Ne and Ne-He collisional broadening and shift of these very narrow Doppler-free two-photon resonances.Doppler-free two-photon transitions between the $3s$, $J=2$ metastable state and the subconfiguration $7{d}^{\ensuremath{'}}$ of neon are studied with a pulsed-dye-laser oscillator-amplifier system which was synchronized with a chopped rf discharge in neon vapor. The isotopic shifts for these transitions are measured, and based on these measurements we have made a systematic study of Ne-Ne and Ne-He collisional broadening and shift of these very narrow Doppler-free two-photon resonances.

Physical Review AFeb 1, 197816 citations

Doppler-free two-photon transitions between the

3s

J=2

metastable state and the subconfiguration $7{d}^{\ensuremath{'}}$ of neon are studied with a pulsed-dye-laser oscillator-amplifier system which was synchronized with a chopped rf discharge in neon vapor. The isotopic shifts for these transitions are measured, and based on these measurements we have made a systematic study of Ne-Ne and Ne-He collisional broadening and shift of these very narrow Doppler-free two-photon resonances.