Double-Rydberg spectroscopy of the barium atom

Abstract

Methods of excitation and analysis of double-Rydberg states of the neutral barium atom are discussed. Spectra of 9dn′d double-Rydberg series of barium are studied and interpreted in a two-channel quantum-defect model. An example of stabilization for the 9d5/227d state is shown. We propose a new investigative method for Rydberg levels of the Ba+ ion that is based on a microwave-ionization process coupled with a double time-of-flight mass spectrometer. This novel setup permits us to obtain initial experimental evidence of highly excited double-Rydberg states, 26dn′p and 27sn′p (n′ ≳ 45), of the barium atom.