Knowledge Bank

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$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$P$\mathrm{<mrow\; data-mjx-texclass="ORD">1<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$($\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi 1/2$) 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$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$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'$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$P($\Pi$)$\leftarrow$6$^{2}$P${1/2}$($^{2}\Pi{1/2}$)andn\prime$^{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$N$ 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. %.