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Physical Review Letters

Collision-Induced Ramsey Resonances in Sm Vapor

Egbert Buhr, J. Mlynek

Published Sep 15, 1986• 18 citations
Publisher

Abstract

We report on the observation of novel Ramsey-type resonances due to collisional velocity diffusion in atomic samarium vapor in the presence of rare-gas perturbers. The experimental technique uses counterpropagating laser fields and relies on coherent resonance Raman processes to optically excite and detect sublevel coherence within the Doppler-broadened $^{154}\mathrm{Sm}$ $\ensuremath{\lambda}=570.68$-nm $^{7}F_{1}\ensuremath{-}^{7}F_{0}$ transition. The experimental findings are in good agreement with theoretical predictions based on a Fokker-Planck equation; time constants for the collisional thermalization of Sm in He and Ne atmospheres are derived from our data.

DOI
10.1103/physrevlett.57.1300

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Collision-induced Ramsey resonances in Sm vapor

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We report detailed studies of Ramsey-type resonances due to collisional velocity diffusion of Sm atoms within the Doppler-broadened $^{7}\mathrm{F}_{1}$\ensuremath{\rightarrow}${\mathrm{}}^{7}$${\mathrm{F}}_{0}$ $^{154}\mathrm{Sm}$ transition at \ensuremath{\lambda}=570.68 nm in the presence of rare-gas perturbers (He,Ne,Ar,Kr,Xe). The experimental technique uses counterpropagating laser fields and relies on coherent resonance Raman processes to excite and detect sublevel coherence optically. A modulated pump laser field is used for velocity-selective resonance Raman excitation of oscillating Zeeman coherence in the J=1 ground state of Sm; the sublevel coherence is monitored by Raman heterodyne detection using a counterpropagating, unmodulated probe laser field. If the pump and probe fields interact with different atomic velocity subgroups, a signal only occurs in the presence of velocity-changing collisions which provide a transport of the Sm atoms with sublevel coherence in velocity space. The sublevel resonance curves turn out to be sensitive to both depolarizing and velocity-changing collisions; the measured line shapes show the characteristic features of Ramsey-type resonances. Our theoretical treatment is based on a novel four-level density matrix calculation; the analysis reveals that the temporal evolution of the collisional velocity-diffusion processes can simply be obtained by means of a Fourier transformation of the measured sublevel resonance curves. In the case of He perturbers the diffusion in velocity space can be described by a Fokker-Planck equation; here, the theoretical fits of the measured sublevel resonance curves directly yield the time constant for collisional thermalization and the cross section for depolarizing collisions. In the case of the heavier rare gases, however, the Fokker-Planck model fails to describe the velocity thermalization; here, the Keilson-Storer kernel yields a better agreement with the experimental data. We derive cross sections for depolarizing and velocity-changing collisions and values for the collisional velocity changes associated with orientation-preserving collisions.

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Observation of Light-Pressure-Induced Dispersion in Yb Vapor

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We report on the observation of a light-pressure-induced dispersion of laser light interacting with a Doppler-broadened atomic medium. This novel dispersion feature displays an even symmetry with respect to the optical Doppler detuning; it is due to the small modification of the atomic velocity distribution caused by the spontaneous scattering force. Our phase-sensitive measurements were performed on the $\ensuremath{\lambda}=555.65$ nm $^{1}S_{0}\ensuremath{-}^{3}P_{1}$ transition in ytterbium vapor by the use of frequency-modulation spectroscopy. The experimental results are in good agreement with theoretical predictions.

Physical Review Letters•Nov 14, 1988•13 citations
We report on the observation of novel Ramsey-type resonances due to collisional velocity diffusion in atomic samarium vapor in the presence of rare-gas perturbers. The experimental technique uses counterpropagating laser fields and relies on coherent resonance Raman processes to optically excite and detect sublevel coherence within the Doppler-broadened 154Sm^{154}\mathrm{Sm}154Sm \ensuremathλ=570.68\ensuremath{\lambda}=570.68\ensuremathλ=570.68-nm 7F1\ensuremath−7F0^{7}F_{1}\ensuremath{-}^{7}F_{0}7F1​\ensuremath−7F0​ transition. The experimental findings are in good agreement with theoretical predictions based on a Fokker-Planck equation; time constants for the collisional thermalization of Sm in He and Ne atmospheres are derived from our data.
We report detailed studies of Ramsey-type resonances due to collisional velocity diffusion of Sm atoms within the Doppler-broadened 7F1^{7}\mathrm{F}_{1}7F1​\ensuremath{\rightarrow}7{\mathrm{}}^{7}7F0{\mathrm{F}}_{0}F0​ 154Sm^{154}\mathrm{Sm}154Sm transition at \ensuremath{\lambda}=570.68 nm in the presence of rare-gas perturbers (He,Ne,Ar,Kr,Xe). The experimental technique uses counterpropagating laser fields and relies on coherent resonance Raman processes to excite and detect sublevel coherence optically. A modulated pump laser field is used for velocity-selective resonance Raman excitation of oscillating Zeeman coherence in the J=1 ground state of Sm; the sublevel coherence is monitored by Raman heterodyne detection using a counterpropagating, unmodulated probe laser field. If the pump and probe fields interact with different atomic velocity subgroups, a signal only occurs in the presence of velocity-changing collisions which provide a transport of the Sm atoms with sublevel coherence in velocity space. The sublevel resonance curves turn out to be sensitive to both depolarizing and velocity-changing collisions; the measured line shapes show the characteristic features of Ramsey-type resonances. Our theoretical treatment is based on a novel four-level density matrix calculation; the analysis reveals that the temporal evolution of the collisional velocity-diffusion processes can simply be obtained by means of a Fourier transformation of the measured sublevel resonance curves. In the case of He perturbers the diffusion in velocity space can be described by a Fokker-Planck equation; here, the theoretical fits of the measured sublevel resonance curves directly yield the time constant for collisional thermalization and the cross section for depolarizing collisions. In the case of the heavier rare gases, however, the Fokker-Planck model fails to describe the velocity thermalization; here, the Keilson-Storer kernel yields a better agreement with the experimental data. We derive cross sections for depolarizing and velocity-changing collisions and values for the collisional velocity changes associated with orientation-preserving collisions.
We report new results on the effect of collisions on radio-frequency (rf) -laser double resonances in an atomic vapor under conditions of velocity-selective optical pumping. Our experiments are performed on Zeeman resonances in the 4${f}^{6}666{s}^{2}$ 7{\mathrm{}}^{7}7F1{F}_{1}F1​--4${f}^{6}$6s6p 7{\mathrm{}}^{7}7F0{F}_{0}F0​ transition in samarium vapor in the presence of rare-gas perturbers (He, Ne, Ar, Xe). The collisional relaxation of the rf-generated sublevel coherence is studied using Raman heterodyne detection; this recently introduced spectroscopic technique is capable of separately yielding signal contributions originating from optically resonant and off-resonant atoms. The corresponding measurements clearly reveal that velocity-changing collisions (VCC) can completely determine the characteristics of the rf-laser double-resonance signals. Our experimental findings on the linewidths and line shapes of the rf resonances are in satisfactory quantitative agreement with theoretical predictions that are based on a novel four-level density-matrix calculation; here a Keilson-Storer collision kernel is used to describe the velocity diffusion processes. The comparison of calculated and measured results also permits us to derive cross sections for VCC and depolarizing collisions; moreover, information on the spectrum of the velocity changes connected with alignment-preserving collisions can be obtained.
We examine experimentally and theoretically the Ramsey effects on the coherent population trapping (CPT) resonance in a paraffin-coated Rb vapor cell. The observed CPT spectrum in the Hanle configuration of the 5S 1/2(F = 2)−5P 1/2(F′ = 1) transition of 87Rb atoms consists of a narrow structure with a spectral width of 0.10 mG due to the wall-induced Ramsey effect and a broad structure with a spectral width of 23 mG due to the transit effect. Considering the velocity distribution of atoms and the number of wall-atom collisions, we numerically calculated the transmittance of the laser beam as a function of the longitudinal magnetic field. The experimental results of the CPT Ramsey interference were in good agreement with the theoretical results, and the dependences of the CPT Ramsey effects on the atom-laser interaction time were investigated in detail.
Raman-Ramsey interference has proved a very effective technique to implement compact and high performing vapor cell frequency standards. In this paper, we theoretically characterize Raman-Ramsey resonances in an optically thick atomic vapor. Specifically, some parameters of interest for frequency standards applications, like contrast and linewidth of the central Raman-Ramsey fringe, are evaluated at different temperatures for 133Cs^{133}\mathrm{Cs}133Cs and 87Rb^{87}\mathrm{Rb}87Rb vapor cells with buffer gas. Density narrowing and broadening effects are described and explained in terms of a three-level theory where laser field propagation through the atomic medium is taken into account. Also, we investigate light shift both in low and high atomic density regimes. Light shift, which potentially degrades the medium- to long-term stability of Raman-Ramsey clocks, is composed of two contributions. The first is a pulling effect exerted by the wide Rabi profile enclosing the interference pattern on the central Raman-Ramsey fringe. The second light-shift term is strictly related to the detection time. Calculations derived from our model well describe already existing experimental results and new behaviors are predicted.
We report on the observation of a light-pressure-induced dispersion of laser light interacting with a Doppler-broadened atomic medium. This novel dispersion feature displays an even symmetry with respect to the optical Doppler detuning; it is due to the small modification of the atomic velocity distribution caused by the spontaneous scattering force. Our phase-sensitive measurements were performed on the $\ensuremath{\lambda}=555.65$ nm $^{1}S_{0}\ensuremath{-}^{3}P_{1}$ transition in ytterbium vapor by the use of frequency-modulation spectroscopy. The experimental results are in good agreement with theoretical predictions.