Observation of 7pP2 3/2 →7dD2 optical transitions in 209 and 210 francium isotopes.

We report on the direct experimental observation of the 7p(2)P(3/2) -> 7d(2)Doptical transitions in 209 and 210 francium isotopes. By continuously monitoring the fluorescence emitted by the isotopes collected in a magneto-optical trap (MOT), the electric dipole transitions 7p(2)P(3/2) -> 7d(2)D(5/2) of Fr-209, not yet experimentally observed, and 7p(2)P(3/2) -> 7d(2)D(5/2), 7p(2)P(3/2) -> 7d(2)D of Fr-210 were detected as subDoppler depletion dips of the cold atom population. This approach allowed unambiguous identification of the excited state hyperfine structures, even in the absence of a large stable vapor. Our findings demonstrate the effectiveness and the flexibility of fluorescence monitoring of trap depletion upon laser excitation, and broaden the experimental knowledge of franciumisotopes and their electronic and nuclear properties. These results will have a relevant impact on ongoing researches for low-energy testing of fundamental symmetries with francium, from atomic parity non-conservation to the electron dipole moment. (C) 2017 Optical Society of America