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Chinese Physics Letters

Self-focusing and self-defocusing due to collision-induced Zeeman coherence

Gong Qi-Huang, Xiangmei Wang, Y. H. Zou

Published Oct 1, 1988• 1 citation
Publisher

Abstract

The continuous wave self-focusing and self-defocusing in sodium vapor have been observed at zero magnetic field. The effects are enhanced by collisions and can be observed in low light intensity and large frequency detuning from the resonance transition. All experimental results can be well explained by collision-induced Zeeman coherence.

DOI
10.1088/0256-307x/5/10/003

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The continuous wave self-focusing and self-defocusing in sodium vapor have been observed at zero magnetic field. The effects are enhanced by collisions and can be observed in low light intensity and large frequency detuning from the resonance transition. All experimental results can be well explained by collision-induced Zeeman coherence.
We report steady-state self-focusing, self-trapping, and self-defocusing of a cw dye laser beam in sodium vapor for frequencies within several Doppler widths of the DDD-line resonance transitions. We measured the variation of the beam profile as the light propagates through the vapor. We observed a 20-mW beam self-trapped in a 12-cm-long filament having a half-power diameter of 70 \ensuremath{\mu}m.
We report steady-state self-focusing, self-trapping, and self-defocusing of a cw dye laser beam in sodium vapor for frequencies within several Doppler widths of the DDD-line resonance transitions. We measured the variation of the beam profile as the light propagates through the vapor. We observed a 20-mW beam self-trapped in a 12-cm-long filament having a half-power diameter of 70 \ensuremath{\mu}m.
Summary form only given. The interaction between an intense pump beam and a weak probe beam in an atomic vapor has been the subject of numerous investigations. Besides the well-known features in the frequency spectrum of the light, interesting spatial phenomena are observed. They are due to the inhomogeneous intensity distribution of a laser beam, coupled to propagation, and range from self-focusing or defocusing effects to the generation of localized distributions of light that propagate self-similarly (bright or dark solitons). We investigate the reshaping of a probe beam due to the interaction with a pump in sodium vapor, a problem that is important in many different contexts.
Near-resonant four-wave light mixing in Na vapor with inert buffer gases reveals collision-induced coherences when the difference frequency between two incident light beams equals the hyperfine splitting or the Zeeman splitting between two states of the 32S3^{2}S32S ground-state manifold. The Doppler broadening of the corresponding resonances decreases with increasing buffer-gas pressure. The width of the resonances becomes significantly narrower than the spontaneous linewidth of the near-resonant intermediate state and is determined by spin-exchange collisions between ground-state atoms. The dependence of the intensity of these collision-induced resonances on buffer-gas pressure and detuning from one-photon resonances is measured. Selection rules for various polarizations of the incident light fields and directions of an externally applied magnetic field are established.
The effect of spin-exchange collisions on the state populations obtained in an optically pumped Na23{\mathrm{Na}}^{23}Na23 vapor is studied in the limit of low light intensity. These state populations and hence the intensity of the rf Zeeman transitions are found theoretically to depend strongly on the spin-exchange cross sections. The various Zeeman rf transitions are found experimentally to be very different in intensity and this is interpreted as being partially due to spin-exchange collisions. From the intensity of the rf transitions in a magnetic field large enough to separate the six Zeeman components and from the observed relaxation time a spin-exchange cross section for two sodium atoms of $\ensuremath{\pi}{{S}_{0}}^{2}=6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ cm2{\mathrm{cm}}^{2}cm2 is found.