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Abstract

The excitation of the 8 eV $^{229m}$Th isomer through the electronic bridge
mechanism in highly charged ions is investigated theoretically. By exploiting
the rich level scheme of open $4f$ orbitals and the robustness of highly
charged ions against photoionization, a pulsed high-intensity optical laser can
be used to efficiently drive the nuclear transition by coupling it to the
electronic shell. We show how to implement a promising electronic bridge scheme
in an electron beam ion trap starting from a metastable electronic state. This
setup would avoid the need for a tunable vacuum ultraviolet laser. Based on our
theoretical predictions, determining the isomer energy with an uncertainty of
$10^{-5}$ eV could be achieved in one day of measurement time using realistic
laser parameters.