Photoionization of the6P32,122fine-structure levels in cesium

The relative photoionization cross sections for cesium atoms selectively excited to the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^{}{}_{}{}^{}$ states have been measured in a triple-crossed-beam experiment. A cesium discharge lamp produced resonant wavelengths of 8521 and 8944 Å for the excitation process. A Hg-Xe lamp combined with a grating monochromator was used for the actual ionization in the wavelength region from 2500 to 5000 Å. Background counts due to photoionization of ground-state cesium atoms and dimers as well as various surface effects were discriminated against by chopping the excitation light source. The data are compared with results from radiative-recombination measurements in which the fine-structure levels are not resolved and with recent model-potential calculations. The wavelength ($\lambda$) dependence of the cross section indicates a ${\lambda }^2$ dependence at threshold (≈ 5000 Å) and a ${\lambda }^4$ behavior at lower wavelengths.