Laser Cooling and Magnetic Trapping of Neutral Atoms

Abstract

Laser cooling is the compression of the velocity distribution of an atomic sample (e.g., atomic beam) by momentum exchange with laser light [1,2]. It can be achieved by exploiting the Doppler shift to assure that fast atoms are decelerated more than slow ones [3,4]. It has been developed in part to ameliorate the effects of two distinct limits to ultrahigh resolution spectroscopy and atomic clocks caused by the thermal motion of atoms. One of these arises from the linewidth produced by the finite interaction time between the measuring equipment and rapidly moving atoms. At a typical thermal speed of 1000 m/s, an experimenter has only a few milliseconds to interact with free atoms in an apparatus of reasonable size (i.e., few meters). The other limit arises from the relativistic time differences between reference frames in relative motion (second order Doppler effect). Although atoms in a thermal beam have a velocity distribution characterized by the temperature of their source, and even though this can be calculated, the details of the distribution at the low velocity end depend very sensitively on the details of the source, and sometimes cannot be adequately known. A sample of slowly moving or monovelocity atoms produced by laser cooling can therefore provide a substantial improvement in spectroscopic resolution [5].