Physical Review
Self-Broadening of Cesium Resonance Lines at 8521 and 8944 Å
C. L. Chen, A. V. Phelps
Abstract
Absorption profiles of cesium resonance lines at 8521 and 8944 \AA{} have been measured for the wavelength range from 0.5 to 30 \AA{} from the line centers using a tungsten ribbon light source, cell lengths $L$ from 0.31 to 6.1 cm, and Cs densities $N$ from 2 \ifmmode\times\else\texttimes\fi{} ${10}^{14}$ to 2 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The wavelength dependence of the absorption coefficients are consistent with a Lorentzian form and values of $\frac{\ensuremath{\gamma}f}{N}=1.08\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ and 0.30 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ are obtained for 8521 and 8944 \AA{} lines. Here $\ensuremath{\gamma}$ is the collisional (or Lorentzian) half-width and $f$ is the oscillator strength. The values of $\frac{\ensuremath{\gamma}f}{N}$ deduced from total fractional absorption data agree with those determined from the line profiles. Our results agree well (to within 15%) with those of Gregory and with theory, but disagree with more recent data. A source of error in some previous determinations of half-widths is the fact that even when the calculated absorption is very large, the measured transmission at the line center is significant; about 3.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ compared to \ensuremath{\sim} ${10}^{\ensuremath{-}100,000}$ predicted from our measurements in the wings of the lines for $N=1.14\ifmmode\times\else\texttimes\fi{}{10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and $L=5.9$ cm. This effect is shown to result from transmission through the monochromator at wavelengths in the far wings of the instrument function.