Atom laser involves amplification process analogous to stimulated emission

Atom laser involves amplification process analogous to stimulated emission

The last objection to the appellation "laser" for experimental atom lasers has been overruled by researchers at the Massachusetts Institute of Technology (MIT; Cambridge, MA). Optical lasers produce light that is monochromatic and coherent by stimulated emission. Last year the MIT group, led by Wolfgang Ketterle, demonstrated that atom pulses emitted from a Bose-Einstein condensate (BEC) were coherent (see Laser Focus World, March 1997, p. 16). Now they have shown that the BEC forms by an amplification process analogous to stimulated emission.

By optically cooling and trapping sodium atoms and then evaporatively cooling them to about 1 µK, a cigar-shaped atom cloud was formed. Illumination of this BEC cloud with a faint probe laser beam at a detuning of 1.7 GH¥allowed the grou¥to observe its evolution via a high-speed charge-coupled-device camera over periods of about 300 to 400 ms, in steps ranging from 5 to 25 ms. The results suggest that the condensation occurred in two steps: a fast relaxation that produces an oversaturated thermal cloud, followed by a slower growth of the condensate within the thermal cloud--a Bosonic stimulation distinctly different from simple relaxation.