Quantify inhomogeneous broadening of the 229Th:CaF2 nuclear transition

Determine the degree of inhomogeneous broadening of the 8.4 eV (2020 THz) 229Th nuclear isomeric transition in a calcium fluoride (CaF2) host crystal arising from variations in the local crystal environment, as observed in quadrupole-resolved lines measured by vacuum-ultraviolet frequency comb spectroscopy.

Background

The study measures four strong electric-quadrupole-resolved transitions of the 229Th nuclear isomer in a CaF2 crystal at three temperatures (150 K, 229 K, 293 K) using a VUV frequency comb. While MHz-level temperature-dependent shifts and splittings are characterized with kilohertz precision, the laser’s ~300 kHz linewidth limits the ability to fully resolve environmental broadening.

In the Discussion, the authors explicitly state that the degree of inhomogeneous broadening from the crystal environment is not yet known, suggesting that narrower comb linewidths would enable a direct measurement. They note the transitions have a maximum inhomogeneous linewidth on the order of ~100 kHz, but a precise quantification remains to be established.