| Trapped Rb atoms have been used as a target for electron excitation cross section measurements out of the laser excited 5P level and into the 6S, 7S, 5 P, 6P, 4D, and 5D levels of Rb. A high fraction of the trapped atoms can be kept in the excited 5P level by laser absorption. Measurements can be made of the fraction of atoms in the excited 5P level and turn the lasers off to produce a target with all the atoms in the ground level. Measurements of the fluorescence from the excited level atoms produced by a pulsed electron beam are made with a 5P/5S mixed level target and a pure 5S ground level target. From the excited level fraction and the known ground level excitation cross section we obtain the cross section for excitation out of the excited 5P level and into the 7S, 5P, and 5D excited levels. Targets containing different excited level fractions have been used, and the resulting excitation cross sections out of the 5P level have been found to be independent of the excited level fractions, confirming the validity of our method. Systematic measurements of this type provide an understanding of the dynamics of atoms in excited levels. |
