Two possible techniques for determining sodium densities in nonhomogeneous optically thick plasmas are investigated. The first one is singlehyphen;mode dyehyphen;laser scattering in the near wings of the sodiumD1andD2resonance lines. The second technique is nearhyphen;resonant twohyphen;photon absorption with two counterpropagating singlehyphen;mode dyehyphen;laser beams and detection of the fluorescence. In both cases, the laser frequency(ies) is (are) detuned far enough from (the intermediate) resonance to make the plasma optically thin for the laser beam(s) and for the directly scattered light, hence for the onehyphen;step twohyphen;quantum transitions. In the scattering experiment, the polarization properties of the scattered light are used for discrimination against the stepwise absorptionhyphen;reemission (the collisionhyphen;induced fluorescence). In the twohyphen;photon absorption experiment, the residual Doppler broadening is small enough to make a clear distinction between the direct twohyphen;quantum and the collisionhyphen;induced stepwise onehyphen;quantum transitions. It is shown that the nearhyphen;wing scattering directly yields local sodium densities. This is not the case for the twohyphen;photon absorption. The technique of nearhyphen;resonant scattering is also applicable to other metal vapors in discharges and neutral gases.
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