HIGHLY EXCITED STATES OF Cs ATOMS ON HELIUM NANODROPLETS
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Date
2011
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Ohio State University
Abstract
Cs atoms on the surface of helium nanodroplets have been excited to high lying nS (n = 8-11), nP (n = 8-11), and nD (n = 6-10) levels. A two-step excitation scheme via the 6$^{2}$P$_{1/2}$($^{2}\Pi_{1/2}$) state using two cw lasers was applied. This intermediate state has the advantage that a large fraction of the excited Cs atoms does not desorb from the helium nanodroplets. An absorption spectrum was recorded by detecting laser induced fluorescence light from the 6$^{2}$P$_{3/2}\rightarrow$6$^{2}$S$_{1/2}$ transition. The pseudo-diatomic model for helium nanodroplets doped with single alkali-metal atoms holds for the observed spectrum. An investigation of spectral trends shows that the n'$^{2}$P($\Pi$)$\leftarrow$6$^{2}$P$_{1/2}$($^{2}\Pi_{1/2}$) and n'$^{2}$D($\Delta$)$\leftarrow$6$^{2}$P$_{1/2}$($^{2}\Pi_{1/2}$) (n' $>$ 9) transitions are lower in energy than the corresponding free-atom transitions. This indicates that the Cs*--He$_\textrm{\scriptsize{N}}$ potential becomes attractive for these highly excited states. \\ Our results suggest a possibility of generating an artificial super-atom with a positive ion core inside a helium nanodroplet and the electron outside, which will be subject to future experiments. %.
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Author Institution: Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria