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Physical Review A

Electromagnetically induced gratings in a degenerate open two-level system

George C. Cardoso, J. W. R. Tabosa

Published Feb 4, 2002• 129 citations
Publisher

Abstract

We have experimentally investigated laser diffraction on electromagnetically induced gratings in a degenerate open two-level system. The experiment employs the standard backward four-wave mixing configuration and the open ${6S}_{1/2}(F=4)\ensuremath{\rightarrow}{6P}_{3/2}{(F}^{\ensuremath{'}}=4)$ transition of cold cesium atoms. Population and coherence gratings are accessed for different relative polarizations of the incident laser beams. Natural and subnatural linewidths are observed depending on which frequency of the incident beams is scanned and reveal the effect of the atomic motion on the diffraction spectra. A simple theoretical model using a three-level $\ensuremath{\Lambda}$ system is in reasonable agreement with the observed results and allowed us to make a close connection with the phenomenon of electromagnetically induced transparency.

DOI
10.1103/physreva.65.033803

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We have experimentally investigated laser diffraction on electromagnetically induced gratings in a degenerate open two-level system. The experiment employs the standard backward four-wave mixing configuration and the open 6S1/2(F=4)\ensuremath→6P3/2(F\ensuremath′=4){6S}_{1/2}(F=4)\ensuremath{\rightarrow}{6P}_{3/2}{(F}^{\ensuremath{'}}=4)6S1/2​(F=4)\ensuremath→6P3/2​(F\ensuremath′=4) transition of cold cesium atoms. Population and coherence gratings are accessed for different relative polarizations of the incident laser beams. Natural and subnatural linewidths are observed depending on which frequency of the incident beams is scanned and reveal the effect of the atomic motion on the diffraction spectra. A simple theoretical model using a three-level \ensuremathΛ\ensuremath{\Lambda}\ensuremathΛ system is in reasonable agreement with the observed results and allowed us to make a close connection with the phenomenon of electromagnetically induced transparency.
Summary form only given. The demonstration of electromagnetically induced transparency (EIT) on an atomic transition along with its potential possibilities of applications has driven a much deeper investigation on the atom-field interaction, specifically concerning to the level degeneracy. This coherent response of an atomic system can also be studied through four-wave mixing (FWM), a process named electromagnetically induced grating (EIG) which present the advantage of being a background free technique. In this work we present results on the observation of subnatural EIG resonance in a degenerate open two-level system where the Zeeman degeneracy plays a important role. The experiment is performed in cold cesium atoms obtained from a MOT and employs the conventional backwards FWM configuration.
Coherent spectroscopy of degenerate two-level systems of the Doppler-broadened D2{D}_{2}D2​ cesium line has been performed in vacuum and in buffer gas cells. Subnatural-width (SNW) electromagnetically induced transparency and electromagnetically induced absorption (EIA) resonances have been observed with single-frequency laser excitation for different light polarizations and collision regimes. SNW-EIA resonances with linearly polarized excitation of the Fg=4{F}_{g}=4Fg​=4 level are observed, and they increase their contrast with power density increase and reach a contrast of 20% at $200 \mathrm{mW}{\mathrm{cm}}^{\ensuremath{-}2}.$ A theoretical model has been elaborated, taking into account the Doppler broadening of the transitions, the linewidth of the laser light, and the experimental conditions for observation of the fluorescence. Here the theoretical results are in agreement with those of the experiment. In a buffer gas cell, the SNW resonances in the fluorescence, in degenerate two-level systems are observed for the first time and they are only obtained with circularly polarized light. A theoretical explanation of this result is proposed. At the expense of contrast, in the presence of a buffer gas the coherent resonances are significantly narrower than in a vacuum cell for the same power density. The observation of SNW resonances in buffer gas is significantly less sensitive to the laser frequency drift than in a vacuum cell, which could be advantageous for applications in metrology and in the measurement of weak magnetic fields.
Employing two lasers as the coupling and probe fields which have opposite circular polarization (σ + and σ -), electromagnetically induced transparency (EIT) in Λ-type Zeeman sublevels of cesium 6 2S 1/2F=3-6 2P 3/2F′=2 degenerate two-level system has been demonstrated via probe absorption spectra. The effect of the intensity and detuning of different coupling. Laser on EII was also investigated in experiments. Within the Doppler background, optical pumping among Zeeman sub-levels and the population of different Zeeman sub-levels can dominate the intensity of EIT effect. And the physical reason of the rugged spectra are presented qualitatively.
Employing an intense laser field coupling to the degenerate two-level system of cesium 6 2S_ 1/2(F=4)- 6 2P_ 3/2(F′=5) transition in a cesium vapor cell, electromagnetically induced absorption (EIA) has been demonstrated via probe absorption spectra, at the same time, electromagnetically induced transparency (EIT) of V-type three-level scheme has been demonstrated on the F=4-F′=3 and F=4-F′=4 transition frequency. The EIA is affected by the intensity and detuning of the coupling laser. By analyzing the effect of optical pumping between Zeeman sub-levels on the EIA and the coherent interactions between multiple degenerate two-level atoms, it is shown that the optical pumping affects the population of different Zeeman sub-levels and the number of the involved two-level atoms, the coherent time between the sub-levels is then changed and the linewidth and intensity of the EIA are affected accordingly.