MagnetoOptical Trapping of Stark Slowed Metastable Helium Atoms

Magneto-Optical Trapping of “Stark. Slowed” Metastable Helium Atoms R. 1 Jung , R. 2 Schumann , S. 1 Gerlach , T. 1 Kwapien , U. 2 Eichmann , G. von Max-Born-Institut 1 Oppen 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. 2 A, D-12489 Berlin 1 principle of laser cooling by the use of the Stark effect goal : - study of ionisation dynamics of metastable helium atoms in a trap - energy levels of helium up to n = 3 - results of laser cooling - cold collisions of ultraslow He* stark-shift of the 33 P-multiplett - storage of metastable helium atoms in an electro-dynamical trap 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 U 3 = 25, 1 k. V. vstart ~ 1000 m/s energy [GHz] energy [cm-1] - realization of a storage-ring for slow helium atoms electric field [k. V/cm] 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. energy [MHz] characteristics of the used diode lasers for transversal cooling and trapping stark-splitting of the 33 P 2 -niveau discharge polarisability : ascalar(33 P) = 4. 279 MHz/(k. V/cm)2 atensor(33 P) = 0. 084 MHz/(k. V/cm)2 ascalar(23 S) = 0. 076 MHz/(k. V/cm)2 spectrum electric field [k. V/cm] beat signal fixed applied voltage - first two field plates: detuning - longitudinal cooling laser detuning - MOT diode laser: U 1 = 12, 1 k. V; U 2 = 18, 6 k. V Dn ~ -2, 3 GHz Dn ~ -8 MHz trapping of metastable helium atoms in a magneto-optical trap 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. Shown is the loading and the decay of our MOT. field-gradient (z-axis) : d. B/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 outlook trapping and guiding He* atoms by means of dynamical electric fields electrodes : 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*. U 4 U 1 calculated trajectory : U 3 U 2 applied voltage (U 1, U 2) Getting a closed trajectory of a trapped atom, we used following parameters: applied voltage (U 3, U 4) trap dimensions: distance of the rods radius of the rods 8 mm 2 mm applied voltage : frequency of the applied voltage : U = 20, 0 k. V n = 3000 Hz