Absolute frequency measurement of the magnesium intercombination transition $^1S_0 \to ^3P_1$

TL;DR

This paper reports a highly precise frequency measurement of the magnesium intercombination transition using a femtosecond laser comb, significantly improving accuracy and enabling calculation of other optical transitions in magnesium isotopes.

Contribution

It presents the first measurement of the magnesium intercombination transition with six orders of magnitude increased accuracy using a femtosecond laser frequency comb.

Findings

Achieved measurement uncertainty of 2.5×10⁻¹².

Determined the transition frequency for $^{24}$Mg, $^{25}$Mg, and $^{26}$Mg.

Estimated short-term instability of 3×10⁻¹³ in one second.

Abstract

We report on a frequency measurement of the $(3s^2)^1S_0\to(3s3p)^3P_1$ clock transition of $^{24}$Mg on a thermal atomic beam. The intercombination transition has been referenced to a portable primary Cs frequency standard with the help of a femtosecond fiber laser frequency comb. The achieved uncertainty is $2.5\times10^{-12}$ which corresponds to an increase in accuracy of six orders of magnitude compared to previous results. The measured frequency value permits the calculation of several other optical transitions from $^1S_0$ to the $^3P_J$-level system for $^{24}$Mg, $^{25}$Mg and $^{26}$Mg. We describe in detail the components of our optical frequency standard like the stabilized spectroscopy laser, the atomic beam apparatus used for Ramsey-Bord\'e interferometry and the frequency comb generator and discuss the uncertainty contributions to our measurement including the first and second order Doppler effect. An upper limit of $3\times10^{-13}$ in one second for the short term instability of our optical frequency standard was determined by comparison with a GPS disciplined quartz oscillator.