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Q: Quantenoptik

Q 17: Poster: Cooling and Trapping

Q 17.20: Poster

Wednesday, April 4, 2001, 12:30–15:00, AT2

Laser Cooling of Metastable Helium by Velocity Selective Coherent Population Trapping in the Presence of Magnetic Fields — •C. Affolderbach^1,2, O. Kritsun¹, and H. Metcalf¹ — ¹Physics Department, State University of New York at Stony Brook, Stony Brook, NY 11794-3800, USA — ²Institute for Applied Physics, Bonn University, Wegelerstraße 8, D-53115 Bonn, Germany

Velocity selective coherent population trapping (VSCPT) provides one of the few purely optical techniques for laser cooling of neutral atoms to temperatures below the one photon recoil limit. The physical process is based on a trapped state involving both internal and external degrees of freedom of the atom which is fed by optical pumping combined with diffusion in momentum space. As this trapped state does not couple to the light fields involved, it does not suffer from photon recoil so that narrow sub recoil widths of the momentum distribution can be reached. We present results of VSCPT applied to transverse cooling of a beam of metastable helium on the 2 ³S → 3 ³P transition in the presence of a magnetic field. Because of the magnetic field, the atoms can be cooled into a narrow momentum distribution centered around a non-zero velocity which is determined by the choice of the magnetic field strength. The metastables are produced in a gas discharge and the atomic transition is excited by 389 nm uv laser light obtained by frequency doubling the output of a titanium-sapphire laser. Due to the large photon recoil of this system it is possible to reach good sub-recoil resolution for measurement of the momentum distribution even with a beam apparatus of moderate size.