Experimental Investigation of Nonergodic Effects in Subrecoil Laser Cooling

Abstract

We present the first detailed investigation of the line shape of the momentum distribution of atoms cooled far below the recoil limit. This distribution is deduced from a direct measurement of the atomic spatial correlation function of metastable helium atoms cooled by velocity-selective coherent population trapping. The measured line shape is then compared to the prediction of an analytical model of this cooling based on Levy statistics. A very good agreement is found between experiment and theory and fundamental features such as self-similarity and nonergodicity are identified.