These processes give the atom a small but not negligible speed and hence the gas has a temperature. If the slowest atoms could be made to neglect all the photons in the optical molasses, perhaps lower temperatures could be reached. But a difficulty was to combine this method with laser cooling. Claude Cohen-Tannoudji and his group between 1988 and 1995 developed a method based on use of the Doppler effect and which converts the slowest atoms to a dark state. He and his colleagues showed that the method functions in one, two and three dimensions.
Intensive development is in progress concerning laser cooling and the capture of neutral atoms.
Among other things, Chu has constructed an atomic fountain, in which laser-cooled atoms are sprayed up from a trap like jets of water. When the atoms turn at the top of their trajectory and start falling again, they are almost stationary. With this technique it is believed that it will be possible to build atomic clocks with a hundredfold greater precision than at present. The technique rewarded this year also forms the basis for the discovery of Bose-Einstein condensation in atomic gases, a phenomenon that has attracted great interest. New Mechanisms for Laser Cooling , by C.N. Cohen-Tannoudji and W.D. Phillips, Physics Today, October 1990, p. 33.