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 6²S_{1 / 2} level to resonant n²D and n²S intermediate states, and represents, to the authors' knowledge, the first such two-photon absorption spectrum of Cs. Transitions from n=9 to 13 have been recorded for the 6²S_{1 / 2}-n²D_{5 / 2,3 / 2} series and from n=11 to 14 for the 6²S_{1 / 2}-n²S_{1 / 2} series.