High-Resolution Electron Spectroscopy of Laser-Excited Ba Rydberg Atoms

Abstract

The ionization of $6sns{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ Rydberg states of ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ has been investigated by high-resolution electron spectroscopy. The Rydberg states were excited by two cw dye lasers via the $6s6p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ level. The electron spectra show rich structure between 0.025 and 3 eV, largely attributable to collisional (Penning) ionization, photoionization, and autoionizing transitions. The first process might be interpreted as superelastic scattering of the Rydberg electron by optically pumped $\mathrm{Ba}\left(6s6p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ or $\mathrm{Ba}\left(6s5d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\right)$ atoms.