Transient Bragg diffraction by a transferred population grating: application for cold atoms velocimetry

We report the observation of transient Bragg diffraction by an optical-pump ing-transferred ground-state population grating in cold cesium atoms confin ed in a magneto-optical trap. The measurement of the grating decay time giv es direct access to the temperature of the cold sample. In principle, the m ethod can be employed to provide directional information on the trap veloci ty distribution. For strong excitation the transferred grating becomes anha rmonic and higher-order diffraction is observed. (C) 1999 Published by Else vier Science B.V. All rights reserved.