Laser Excitation of the Th-229 Nucleus
Johannes Tiedau, M. V. Okhapkin, Ke Zhang, Johannes Thielking, G. Zitzer, E. Peik, Fabian Schaden, Thomas Pronebner, I. Morawetz, L. Toscani De Col, F. Schneider, A. Leitner, Milton L. Pressler, Georgy A. Kazakov, Kjeld Beeks, Tomáš Šikorský, Thorsten Schumm
Abstract
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.