High-precision measurements of electric-dipole-transition amplitudes in excited states of $^{208}$Pb using Faraday rotation spectroscopy

TL;DR

This study achieved high-precision measurements of electric-dipole transition amplitudes in excited states of lead using Faraday rotation spectroscopy, confirming theoretical predictions with sub-1% accuracy.

Contribution

The paper introduces a novel application of Faraday rotation spectroscopy with polarization modulation and lock-in detection to measure E1 transition amplitudes in lead with unprecedented precision.

Findings

Measured two E1 transition amplitudes with sub-1% accuracy

Results agree closely with ab initio calculations

Developed a temperature-controlled spectroscopy setup

Abstract

We have completed measurements of two low-lying excited-state electric-dipole (E1) transition amplitudes in lead. Our measured reduced matrix elements of the $(6s^2 6p^2)^3P_1 \to (6s^2 6p7s)^3P_0$ transition at 368.3 nm and the 405.8 nm $(6s^2 6p^2)^3P_2 \to (6s^2 6p7s)^3P_1$ transition are 1.90(1) a.u. and 3.01(2) a.u. respectively, both measured to sub-1 % precision and both in excellent agreement with the latest $ab \ initio$ lead wavefunction calculations. These measurements were completed by comparing the low-field Faraday optical rotation spectra of each E1 transition in turn with that of the ground-state $^{3}P_0 \to ^{3}P_1$ M1 transition under identical experimental conditions. Our spectroscopy technique involves polarization modulation and lock-in detection yielding microradian-level optical rotation resolution. At temperatures where direct absorption was significant for both E1 and M1 transitions, we also extracted matrix element values from a direct optical absorption depth comparison. As part of this work we designed an interaction region within our furnace which allowed precise determination of our quartz vapor cell sample temperature to provide accurate determination of the Boltzmann thermal population of the low-lying excited states that were studied.