Limitation of sequential laser excitation for double-Rydberg autoionizing states of barium and quantum-defect approach

Abstract
The limitations of methods of excitation and analysis of double-Rydberg states of neutral barium atoms are discussed. Excitation spectra of the type 6snd → 9dn′ d are studied and interpreted in a two-channel quantumdefect model for n ≥ 15. No resonance is observed for n < 15, which fixes the limit of the possibilities of the sequential laser excitation. Similar behavior is observed for excitation spectra 6snp → 26dn′p and 6snp → 27sn′ p for n < 39.