Ionization, excitation of high-lying atomic states, and molecular fluorescence in Cs vapor excited atλ=455.7 and 459.4 nm

We have studied in detail the ionization and population of high-lying atomic states which occur in cesium vapor excited at the second resonance transition, 6S-7P. We have developed a simple model which qualitatively explains the laser-power dependences of level populations and electron densities which we observed. Measurements of spatial dependences of fluorescence point out the critical role of radiation trapping in these phenomena. Similar observations on rubidium demonstrate the same type of behavior when the first (5S-5P) or second (5S-6P) resonance is excited. At higher densities and temperatures we found that the fluorescence was dominated by diffuse molecular bands. Some of these bands probably consist of transitions to the repulsive ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ state. Additionally four bands observed at 817.5, 826.6, 835.3, and 839.6 nm are tentatively identified as the cesium analog of the ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$ ${\to }^3$ ${\mathrm{\Sigma }}_{\mathrm{u}}^{+}$ satellite bands which have previously been observed in the blue wing of the first resonance doublet of the lighter alkali metals.