Hamburg 2009 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 36: Ultra-Cold Atoms, Ions and BEC V (with Q)
A 36.2: Fachvortrag
Freitag, 6. März 2009, 11:00–11:30, VMP 6 HS-C
Laser Cooling and Trapping of Barium — •Lorenz Willmann — KVI, University of Groningen, The Netherlands
The heavy alkaline earth element barium (Ba) offers no single closed optical transition. The strong 6s2 1S0 - 6s6p 1P1 cooling transition at 553.7nm branches with 0.3% into three metastable states. This loss is 100 times larger than for the corresponding transition in the lighter earth-alkali strontium. Repumping was accomplished via the 6s6p 1P1 state at the wavelengths 1108nm, 1130nm and 1500nm. A Ba atomic beam was slowed by light at the cooling and the repump wavelengths and then captured in a magneto optical trap (MOT). A collection efficiency of 1% from the atomic beam was achieved. The capture velocity of the MOT was 30(5) m/s. Three-photon photoionization from the ground state limited the trap lifetimes at higher cooling laser intensities. The multi-laser approach lead to coherent Raman transitions and a large fraction of 0.5(2) of the population in the metastable states. Several branching ratios and lifetimes of highly excited states have been determined, which provide input for atomic structure calculations.
The atomic level scheme of radium (Ra) is similar to Ba and the laser cooling and trapping approach can be transferred. Atomic Ra exhibits large enhancement factors for time reversal and parity violating effects, i.e permanent electric dipole moments (EDMs). The enhancements of up to four orders of magnitude are due to near degenerate states of opposite parity in the atomic and nuclear level structure. An experimental search for EDMs is underway at the TRIµP facility at KVI where short-lived Ra isotopes are available.