Laser and microwave spectroscopy of even-parity Rydberg states of neutral ytterbium and Multichannel Quantum Defect Theory analysis

TL;DR

This paper presents new laser and microwave spectroscopic measurements of high-lying Rydberg states in neutral ytterbium, combined with multichannel quantum defect theory analysis to refine energy levels and ionization limits.

Contribution

It provides the first detailed MQDT analysis of even-parity Rydberg states in ytterbium, improving the accuracy of energy levels and ionization limit estimates.

Findings

Revised ionization limit: 50443.07041(25) cm$^{-1}$

Enhanced accuracy of Rydberg state energies

Comparison with previous models and analysis of differences

Abstract

New measurements of high-lying even parity $6sns\, {}^1 \! S_0$ and $6snd\,{}^{3,1}\!D_2$ levels of neutral $^{174}$Yb are presented in this paper. Spectroscopy is performed by a two-step laser excitation from the ground state $4f^{14}6s^2 \, {}^1 \! S_0$, and the Rydberg levels are detected by using the field ionization method. Additional two-photon microwave spectroscopy is used to improve the relative energy accuracy where possible. The spectroscopic measurements are complemented by a multichannel quantum defect theory (MQDT) analysis for the J=0 and the two-coupled J=2 even parity series. We compare our results with the previous analysis of Aymar {\it{et al}} \cite{Aymar_1980} and analyze the observed differences. From the new MQDT models, a revised value for the first ionization limit $I_{6s}=50443.07041(25)$ cm$^{-1}$ is proposed.