Excitation of the isomeric 229mTh nuclear state via an electronic bridge process in 229Th+.

We consider the excitation of the nuclear transition 229gTh-229mTh near 7.6 eV in singly ionized thorium via an electronic bridge process. The process relies on the excitation of the electron shell by two laser photons whose sum frequency is equal to the nuclear transition frequency. This scheme allows us to determine the nuclear transition frequency with high accuracy. Based on calculations of the electronic level structure of Th+ which combine the configuration-interaction method and many-body perturbation theory, we estimate that a nuclear excitation rate in the range of 10  s⁻¹ can be obtained using conventional laser sources.