Polarization of fluorescence radiation subsequent to inner-shell photoionization:LS-coupling formulas

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The polarization and angular distribution of fluorescence radiation subsequent to inner-shell photoionization in atoms are presented here in the important special case that dynamic amplitudes are calculated in $\mathrm{LS}$ coupling taking full account of anisotropic electron-ion interactions. The resulting formulas require for their evaluation no more dynamical information than is usually obtained in an $\mathrm{LS}$-coupling calculation of the photoionization cross section. Exact geometrical relationships which are obscured in more general treatments become apparent in an $\mathrm{LS}$-coupling formulation. Thus it is shown that in $\mathrm{LS}$ coupling the fluorescence resulting from photoionization of an $s$ subshell in an atom having an initial orbital angular momentum ${L}_{0}=0$ has an analytically known constant polarization. Analytic predictions for the linear polarization of fluorescence radiation resulting from ionization of atoms with ${L}_{0}=0$ by unpolarized light are given and illustrated explicitly for nitrogenlike atoms. Experimental measurements of fluorescence polarizations which deviate from these theoretically exact predictions in $\mathrm{LS}$ coupling are thus a sensitive probe of relativistic and certain weak electron correlation interactions.