Laser ionization scheme development for in-gas-jet spectroscopy studies of Th+

The in-gas laser ionization and spectroscopy (IGLIS) technique has been a cornerstone in the study of heavy elements. The addition of a convergent–divergent (de Laval) nozzle to perform laser ionization in a cold hypersonic gas jet greatly improves the achievable resolution. Recent efforts have focused on preparing the in-gas-jet method for the study of the low-lying 229Th isomer. Tailor-made recoil sources of 233U are installed inside a fast extraction gas cell to provide the (isomeric) thorium ions. A level search above the second ionization potential (IP) uncovered several auto-ionizing states, greatly improving the laser ionization efficiency of singly charged thorium ions.