Energies and hyperfine splittings of the 7D levels of atomic francium

We report optical double-resonance spectroscopy to locate and study the 7D3/2 and 7D5/2 levels of a sample of Fr atoms confined and cooled in a magneto-optical trap. The upper state of the 7P3/2 trapping transition serves as the resonant intermediate level to reach the 7D states. The energy difference to the ground state is measured for the accessible levels. We measure the hyperfine splittings: D(7D3/2 ,F515/2↔13/2)5167 64 MHz, D(7D5/2 ,F517/2↔15/2)52117.562.5 MHz, and D(7D5/2 ,F515/2↔13/2)5212164 MHz. Extrapolating the energies of the inaccessible hyperfine levels from the hyperfine constants and assuming B(7D3/2)50, the center-of-gravity energy difference to the ground state is E(7D3/2)524 244.831 60.003 cm and E(7D5/2)524 333.29860.003 cm .