Multiphoton excitation and ionization of atomic cesium with a tunable dye laser

The two-photon excitation and three-photon ionization of atomic cesium is investigated over the 6550-6950-Å wavelength region with a tunable-dye-laser source having a 0.06-0.08-Å linewidth and a space-charge ionization detector sensitive to a few ions per second. An online data-acquisition computer provides significant signal-to-noise recovery. The resulting dispersion curve for photoionization is interpreted in terms of the two-photon transitions from the ground $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ level to resonant $n{}_{}{}^2{}_{}{}^{}D$ and $n{}_{}{}^2{}_{}{}^{}S$ intermediate states, and represents, to the authors' knowledge, the first such two-photon absorption spectrum of Cs. Transitions from $n=9\mathrm{}\mathrm{to}13$ have been recorded for the $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-n{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2},\frac{3}{2}}^{}{}_{}{}^{}$ series and from $n=11\mathrm{}\mathrm{to}14$ for the $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-n{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ series.