Absolute frequency measurement of the 7s2 1S0 − 7s7p 1P1 transition in 225Ra

Transition frequencies were determined for transitions in Ra in an atomic beam and for reference lines in Te2 molecules in a vapor cell. The absolute frequencies were calibrated against a GPS stabilized Rb-clock by means of an optical frequency comb. The 7s2 1S0(F = 1/2)-7s7p 1P1(F = 3/2) transition in 225Ra was determined to be 621 042 124(2)MHz. The measurements provide input for designing efficient and robust laser cooling of Ra atoms in preparation of a search for a permanent electric dipole moment in Ra isotopes. PACS numbers: 31.30.jp, 11.30.Er, 42.62.Fi, 33.20.-t Radium (Ra) is the heaviest alkaline earth metal and it of-fers unique possibilities for measuring parity and time reversal symmetry violation. The particular atomic and nuclear [1– 8] structure in Ra isotopes cause the largest enhancement for permanent electric dipole moments (EDMs) [9] in any atom. This arises from the close proximity of the 7s7p 3P1 and 7s6d 3D2 states [1]. The exploitation of the enhancement from this 5 cm−1 separation requires precise knowledge of Ra atomic properties such as the absolute frequencies of transi