Two-photon spectroscopy of the francium 8S1/2 level

We report the spectroscopy of the 8S(1/2) energy level in Fr-210 by two-photon excitation of atoms confined and cooled in a magneto-optical trap. The resonant intermediate level is the upper; state of either the 7P(3/2) trapping transition or the 7P(1/2) repumping transition. The center-of-gravity energy difference between the 7S(1/2) ground level and the 8S(1/2) level is 19 732.523 +/- 0.004 cm(-1). The hyperfine separation of the 8S(1/2), F=11/2 and F=13/2 states is 10 256 +/- 7 MHz, giving a magnetic dipole hyperfine constant A of 1577.8+/-1.1 MHz. [S1050-2947(99)01201-9].