Self-Broadening of Cesium Resonance Lines at 8521 and 8944 Å

Abstract

Absorption profiles of cesium resonance lines at 8521 and 8944 Å have been measured for the wavelength range from 0.5 to 30 Å 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 × ${10}^{14}$ to 2 × ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The wavelength dependence of the absorption coefficients are consistent with a Lorentzian form and values of $\frac{\gamma f}{N}=1.\mathrm{}08\times {10}^{-7\mathrm{}}$ and 0.30 × ${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ are obtained for 8521 and 8944 Å lines. Here $\gamma$ is the collisional (or Lorentzian) half-width and $f$ is the oscillator strength. The values of $\frac{\gamma f}{N}$ 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 × ${10}^{-2\mathrm{}}$ compared to ∼ ${10}^{-100,000\mathrm{}}$ predicted from our measurements in the wings of the lines for $N=1.\mathrm{}14\times {10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and $L=5.\mathrm{}9$ cm. This effect is shown to result from transmission through the monochromator at wavelengths in the far wings of the instrument function.