Abstract:
The thorium-229 nucleus with its 8.4 eV isomer is a unique system for studies at the interface between nuclear and atomic physics, with an excitation energy in the range of transition energies of valence electrons, and accessible for the methods of precision laser spectroscopy. After the first resonant laser excitation of the nuclear transition there is strongly increasing activity on this topic. Among the applications, the development of a nuclear clock seems particularly attractive. This clock would offer high accuracy, high stability, and high sensitivity in clock-based tests of fundamental principles of physics, involving the strong interaction in addition to electromagnetism. There are two approaches for realizing such a nuclear clock, using laser Mössbauer spectroscopy of thorium-doped crystals, or laser-cooled thorium ions in radiofrequency ion traps. Recent progress has been made with narrow-linewidth laser sources for the required radiation at 148 nm: We have demonstrated the first CW all-solid-state laser system for this wavelength. In cooperation with the group of Th. Schumm at TU Wien, we show that the nuclear resonance can be probed with a power of less than 1 nW, and that robust clock operation over more than 24 h is possible.
