S C I E N C E Optical Pumping

The term optical pumping refers to the redistribution of atoms among their fineor hyperfine-structure levels by means of light. The resonance radiation of the atom is usually the radiation used. This is selected in some way, specifically by being circularly polarized, anisotropic, filtered, or amplitudemodulated. By unusually simple experimental techniques it is possible to measure the fine and hyperfine structure of atoms, the magnetic moments of radioactive nuclei, the cross sections of a number of interesting processes, and the magnetic properties of free ions and electrons, and to produce useful polarization of atoms, nuclei, and electrons. The techniques have led to the development of two especially useful devices atomic clocks of great simplicity and magnetometers of particular usefulness in measuring the weak magnetic fields of the earth and in space-and the techniques have been at least partly responsible for the development of the coherent light generator, or laser. The research has been pursued with enthusiasm, partly because of the range of applicability of the simple techniques, and partly because of the fascination of work in a field in which the ideas are so obvious that one cannot but wonder why they were not exploited earlier. In the last two decades there have been a number of discoveries, such as magnetic