Laser Excitation of the Th-229 Nucleus

The 8.4 eV nuclear isomer state in Th-229 is resonantly excited in Th-doped CaF_{2} crystals using a tabletop tunable laser system. A resonance fluorescence signal is observed in two crystals with different Th-229 dopant concentrations, while it is absent in a control experiment using Th-232. The nuclear resonance for the Th^{4+} ions in Th:CaF_{2} is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum. These results pave the way toward Th-229 nuclear laser spectroscopy and realizing optical nuclear clocks.

• UD
  U.S. Department of Energy
• DF
  Deutsche Forschungsgemeinschaft

  Awards: SFB 1227, 274200144
• SN
  Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung

  Award: 514788
• AS
  Austrian Science Fund

  Awards: P33627, F1004, 10.55776/F1004, 10.55776/P35891, I5971, 10.55776/I5971
• M
  Max-Planck-Gesellschaft
• H2
  Horizon 2020 Framework Programme

  Award: 856415
• R
  RIKEN
• OR
  Oak Ridge National Laboratory
• HE
  H2020 European Research Council