Absolute frequency measurement of the $6s^2~^1S_0 \to 6s6p~^3P_1$ $F=3/2\to F'=5/2$ $^{\text{201}}$Hg transition with background-free saturation spectroscopy

TL;DR

This paper introduces a background-free saturation spectroscopy method to accurately measure the absolute frequency of a specific mercury atomic transition, overcoming Doppler background issues and referencing to UTC with an optical frequency comb.

Contribution

The authors developed a novel technique to eliminate background-induced shifts in saturation absorption measurements, enabling precise frequency determination of the $^{201}$Hg transition.

Findings

Measured the transition frequency as 1181541111051(83) kHz.

Demonstrated the method's effectiveness on a Doppler background-located spectral line.

Analyzed the dependence of systematic shifts on spectral and background properties.

Abstract

We report the development of a method for eliminating background-induced systematic shifts affecting precise measurements of saturation absorption signals. With this technique, we measured the absolute frequency of the $6s^2~^1\text{S}_0 \to 6s6p~^3\text{P}_1$ transition in $^{201a}\text{Hg}$ ($F=3/2\to F'=5/2$) to be $1181541111051(83)$~kHz. The measurement was referenced with an optical frequency comb synchronized to the frequency of the local representation of the UTC. This specific atomic line is situated on the steep slope of the Doppler background at room temperature, which results in frequency systematic shift. We determined the dependence of this shift on the properties of both the spectral line and the background of the measured signal.