spectrum

1. applied voltage (U1,U2) applied voltage (U3,U4) Max-Born-Institut R. Jung1, R. Schumann2, S. Gerlach1, T. Kwapien1, U. Eichmann2, G. von Oppen1 1 Technische Universität Berlin, Institut für Atomare und Analytische Physik, Hardenbergstrasse 6, D-10623 Berlin 2 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin principle of laser cooling by the use of the Stark effect - energy levels of helium up to n = 3 - results of laser cooling Shown are TOF-spectra of cooled helium atoms taken from the MOT-MCP while varying the applied voltage of the third field plate. The increase of the signal was due to the interaction between the MOT-laser and helium atoms (vatoms ~ 10 m/s) at U3 = 25,1 kV. stark-shift of the 33P-multiplett energy [GHz] energy [cm-1] electric field [kV/cm] stark-splitting of the 33P2-niveau discharge energy [MHz] polarisability :ascalar(33P) = 4.279 MHz/(kV/cm)2 atensor(33P) = 0.084 MHz/(kV/cm)2 ascalar(23S) = 0.076 MHz/(kV/cm)2 electric field [kV/cm] fixed applied voltage - first two field plates: U1 = 12,1 kV; U2 = 18,6 kV detuning - longitudinal cooling laser Dn ~ -2,3 GHz detuning - MOT diode laser: Dn ~ -8 MHz trapping of metastable helium atoms in a magneto-optical trap Shown is the loading and the decay of our MOT. field-gradient (z-axis) : dB/dz = 6,4 Gauss/cm detuning of the MOT-laser : Dn = -7 MHz diameter of the trapping laser beam : d = 2 cm lifetime of the trap : t 240 ms Magneto-Optical Trapping of “Stark-Slowed” Metastable Helium Atoms goal : - study of ionisation dynamics of metastable helium atoms in a trap - cold collisions of ultraslow He* - storage of metastable helium atoms in an electro-dynamical trap - realization of a storage-ring for slow helium atoms vstart ~ 1000 m/s characteristics of the used diode lasers for transversal cooling and trapping For stabilizing the diode lasers we use the mean of saturation spectroscopy. We extract the control signal out of the spectrum of the -transition. The laser linewidth of the diode lasers is determined to about 5 MHz by measuring the beat signal on a fast photodetector. spectrum beat signal transversal cooling and deflection of the He* beam To separate the metastable helium atoms from the ground-state atoms, the He* source is placed off-axis, so that only the metastables will be deflected into the “Stark-slower”-section by the use of the diode laser at l = 1083 nm. outlook trapping and guiding He* atoms by means of dynamical electric fields electrodes : calculated trajectory : U3 U1 Our aim is to construct a trap or an atom-guide for helium atoms based on rotating electric fields. Simulations show the possibility to hold helium atoms with v < 2 m/s against gravity. With variable structures of the rods it will be possible to get a storage-ring for metastable helium atoms, where we can study ultracold collisions of He*. U4 U2 Getting a closed trajectory of a trapped atom, we used following parameters: trap dimensions: distance of the rods 8 mm radius of the rods 2 mm applied voltage : U = 20,0 kV frequency of the applied voltage : n = 3000 Hz