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A: Fachverband Atomphysik
A 2: Precision spectroscopy I
A 2.3: Talk
Monday, March 19, 2007, 11:15–11:30, 6G
Sub-Doppler cooling of magnesium by a coherent two-photon excitation — •Karsten Moldenhauer, Matthias Riedmann, Tanja E. Mehlstäubler, Jan Friebe, Nils Rehbein, André Pape, Alexander Voskrebenzev, Ernst M. Rasel, and Wolfgang Ertmer — Institut für Quantenoptik, Leibniz Universität Hannover, Deutschland
Magnesium belongs to the few elements suitable for an optical frequency standard with neutral atoms. It displays very attractive features such as a low black body radiation shift, long-lived states or the existence of magic wavelength, required for an optical lattice clock. The current stability of 8x10−14 in 1 s and spectroscopic resolution of 290 Hz is limited by the achievable temperatures of about 4 mK in a magneto-optical trap (MOT) based on the fast 1S0→ 1P1 transition .
Standard Sub-Doppler cooling techniques are not applicable to Magnesium due to the absence of a magnetic sub-structure of the ground state. To surpass the Doppler-limit, we utilize a two-photon transition 1P0→ 1D2 to coherently manipulate the population in 1P1. This novel cooling mechanism, similar to electro-magnetically induced transparency, strongly enhances the cooling force.
Experimental results are in good agreement with our theoretical model and show temperature reductions by a factor of 10 in a 1D optical molasses and a factor of 4 in a MOT. Additional cooling times of 1 ms and atom losses below 40 % make this scheme particularly attractive to improve the short-term stability of optical frequency standards and the loading conditions into optical dipole traps for lattice clocks.