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=9to13 have been recorded for the 6²S_1/2-n²D_5/2,3/2 series and from n=11to14 for the 6²S_1/2-n²S_1/2 series.