Dipole structure of planetary atoms

Using resonant multiphoton laser excitation in combination with temporarily applied electric fields we have excited high-lying planetary states in strontium. Thereby, the angular momenta were high enough to prevent penetration of the Sr⁺⁺ core, as well as the mutual penetration of the two excited wave functions. Analysis of the spectra (quantum defects and oscillator strength modulations) clearly revealed the dipole structure of such a ``planetary atom,'' where the outer electron is bound to either a permanent or an induced dipole formed by the inner electron and the ionic core.