Laser Cooling of ^(87)Rb to 1.5µK in a Fountain Clock

We report an experiment on the adiabatic cooling of 87Rb atoms in an atomic fountain to a temperature as low as 1.5μK,which is roughly twice the recoil temperature.The atomic fountain has the(1,1,1)optical geometry for cooling and launching of cold atoms.The atoms are first cooled in an optical molasses of 6 beams to 3.4μK by polarization gradient geometry and then are adiabatically cooled by decreasing the intensity of laser from 1.8Is per beam to zero in 1 ms during the launching of cold atoms.We also study the dependences of atomic temperature on different laser parameters.The method we used is useful in any cold atom physics experiment.