The multiphoton excitation of rubidium has been investigated over the 4600-6500- wavelength region with a tunable dye-laser source having a linewidth better than 0.1 and a space-charge ionization detector sensitive to a few ions per second. Multiphoton transitions have been observed to occur both through intermediate atomic states and through intermediate continuum states of the rubidium molecule. In the former case two-photon transitions have been observed from the 5S2 ground state of atomic rubidium to higher-lying nD2 levels for values of n ranging from 9 to 34 and to n S2 levels for values of n from 11 through 20. The fine-structure intervals of the n D2 levels for n=9toc13 were measured together with the line-strength ratios and were found to be in good agreement with the predictions of a simple theoretical model. At the shorter wavelengths hybrid two-photon resonances were observed to be excited through resonant intermediate continuum states of Rb2. As a result the dispersion curve for two-photon absorption in rubidium showed what appears to be resonant intermediate pπ(u13) and 0g+ terms dissociating to give a 5P32 atom and resulting in the strong development of features corresponding to the 5P322→nD32,522 part of the diffuse series, for n≤50 in absorption and the 5P322→nS122 part of the sharp series. Components to 32D2 and 30S2 were recorded to a precision of 0.3 cm-1 and quantum defects for these previously unobserved terms were derived. The corresponding hybrid two-photon resonances involving intermediate states dissociating to give a 5P122 atom were not observed in the wavelength interval available in this experiment.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics