Laser excitation of the thorium-229 nucleus - towards a nuclear clock

by Dr Ekkehard Peik (PTB, Germany)

Wednesday 11 Feb 2026, 16:00 → 17:00 Europe/London

117 (Physics West)

About two years ago, the first resonant laser excitation of a low-energy nuclear transition, from the ground state of Th-229 to its isomeric state at 8.4 eV has been reported. The experiments used table-top laser systems at a wavelength of 148nm in the vacuum-ultraviolet. The thorium nuclei have been prepared as dopant ions in VUV-transparent crystals like calcium fluoride. This has opened a new and now highly active field of experimental research that connects nuclear physics with atomic physics, where a nuclear transition occurs in the energy range that is typical for transitions of atomic valence electrons. Among several possible applications, the development of an optical nuclear clock seems particularly attractive. This clock will offer high accuracy, especially with laser cooled trapped Th-229 ions, high stability, because of the high number of nuclei that can be interrogated in Th-229-doped solids like in Mössbauer spectroscopy, and high sensitivity in clock-based tests of fundamental principles of physics, involving the strong interaction in addition to electromagnetism.