Relaxation of the sodium atom in the 4D level by collisions with noble gases. I. Experimental aspects

The sodium atom is excited selectively in the 4D3/2 or 4D 5/2 level using Doppler-free two-photon absorption. We analyse the fluorescence in intensity and polarization in presence of noble gas atoms. We measure the cross-sections corresponding to the transfer of population between 4D3/2 and 4D5/2 and between 4D and 4F, the relaxation of alignment in both fine sublevels and the transfer of alignment. In particular, we have observed a transfer of alignment in the case of helium and neon perturbers.