Theoretical Study on Optical-Pumping Self-Focusing

A theoretical study is made on the steady-state self-focusing and self-defocusing of a circularly-polarized laser beam, occurring in an atomic vapor mixed with a buffer gas at a relatively high pressure. The presence of the buffer gas removes the theoretical difficulties arising from hole-burning, the transit time, and hyperfine pumping. It also localizes the optically-pumped atoms in the vicinity of the laser beam, so that self-focusing occurs even at extremely weak light intensities. A preliminary experiment is also descirbed, the results of which show that optical-pumping self-focusing can be observed at laser intensities down to 30 μW.