Laser spectroscopy on the hyperfine structure and isotope shift of sympathetically cooled $^{229}$Th$^{3+}$ ions

Abstract: The hyperfine structure of $^{229}$Th$^{3+}$ ions in the nuclear ground state is investigated via laser spectroscopy of trapped Th$^{3+}$ ions that are sympathetically cooled by laser-cooled $^{88}$Sr$^+$ ions in a linear Paul trap. The isotope shift to $^{230}$Th$^{3+}$ and the hyperfine constants for the magnetic dipole (A) and electric quadrupole (B) interactions for the 5F${5/2}$ and 6D${5/2}$ electronic states of $^{229}$Th$^{3+}$ are determined. These measurements provide nuclear moments of $^{229}$Th with reduced uncertainty and serve as a preparation for improved hyperfine spectroscopy of the 8.4 eV nuclear isomeric state in $^{229}$Th$^{3+}$ ions.