Unlocking the Thorium-229 Frontier: From Nuclear Clocks to Fundamental Physics

We report the first direct laser excitation of the Th-229 nuclear transition in Th-doped CaF2 crystals using a tabletop tunable laser system. The Th: CaF2 crystals are grown at TU Wien with up to 5×1018 cm-3 Th-229 concentration, and a VUV laser system developed at PTB, that provides a spectral photon flux of more than 2×104 photons/(s Hz). A resonance fluorescence signal is observed in two...