Transverse magneto-optical compression of a frequency-chirping, slowed cesium atomic beam

Abstract

We have transversally compressed a monokinetic cesium atomic beam in a 2D MOT1,2 on the F=4→F′=5 transition of the cesium IX, line. The longitudinal cooling was obtained by frequency-chirped diode lasers.3 Preliminary results have been obtained showing a final diameter of about 50pm and a density of 108at./cm3. We have studied the specificities of a multi-V system as the transition F=4→F′=5 in the cesium atom. Originally proposed for a three-level V-type atomic system4, the process can be easily generalized to F→F+1 (F>=1) transitions. In this case, the atom is assumed to be polarized into the Zeeman sub-level Mf=-F with respect to the local magnetic field inside of the trap. For a non-polarized statistic mixture, two effects modify the compression process. The first one is due to the large variation in the Clebsch-Gordan coefficients.3 The second one comes from the difference between the Larmor frequencies associated to the lower and the upper levels. The both effects lead to a mF-dependent restoring force. Efficient compression can be obtained by preparing the atomic population in the “good” Zeeman sub-levels, |MF|=F. Two methods have been explored in our experiments to polarize the atomic beam. The first one used an additional blue-detuned laser beam to increase the atomic population in the |MF|=f Zeeman sub-levels by optical pumping. In the second one, the σ-polarized cooling laser beam orientated the atomic population in the axial direction during the slowing process. This orientation was adiabatically transformed into transversal ones by entering in the trap. Further experiments are in progress.