Improved measurement of the hyperfine structure of the laser cooling level $4f^{12}(^3 H_6)5d_{5/2}6s^2$ $(J=9/2)$ in $^{169}$Tm

TL;DR

This paper presents an improved measurement of the hyperfine structure of a specific excited state in Tm-169, crucial for laser cooling, using Doppler-free spectroscopy and analysis of line broadening mechanisms.

Contribution

The study provides a more precise hyperfine constant measurement and a detailed analysis of line broadening effects in Tm-169 laser cooling transitions.

Findings

Hyperfine constant A_J = -422.112(32) MHz

Energy difference between hyperfine sublevels is -2110.56(16) MHz

Quantitative analysis of line broadening mechanisms

Abstract

We report on the improved measurement of the hyperfine structure of $4f^{12}(^3 H_6)5d_{5/2}6s^2$ $(J=9/2)$ excited state in Tm-169 which is involved in the second-stage laser cooling of Tm. To measure the absolute value of the hyperfine splitting interval we used Doppler-free frequency modulation saturated absorption spectroscopy of Tm atoms in a vapor cell. The sign of the hyperfine constant was determined independently by spectroscopy of laser cooled Tm atoms. The hyperfine constant of the level equals $A_J=-422.112(32)$ MHz that corresponds to the energy difference between two hyperfine sublevels of $-2110.56(16)$~MHz. In relation to the saturated absorption measurement we quantitatively treat contributions of various mechanisms into the line broadening and shift. We consider power broadening in the case when Zeeman sublevels of atomic levels are taken into account. We also discuss the line broadening due to frequency modulation and relative intensities of transitions in saturated-absorption experiments.