7S_1/2→9S_1/2 two-photon spectroscopy of trapped francium

Abstract
We report on the spectroscopic measurement of the 210Fr 9S1/2 energy obtained by two-photon excitation of atoms confined and cooled in a magneto-optic trap. The resonant intermediate level 7P3/2 is the upper state of the trapping transition. We have measured the energy difference between the 9S1/2 state and the 7S1/2 ground state to be 25 671.021 ± 0.006 cm−1.