5B6--Magnetic depolarization of a vapor and polarization of a Zeeman laser

Lamb's self-consistent theory and rate equation approximation are used to determine the polarization of a monomode gas laser subjected to a magnetic field. The excited vapor is represented by a four level system; its motion is described in a Bloch analog form, using Fano formalism. In the stimulated emission (absorption) process, atoms and light are shown to exchange energy and angular momentum. This optically induced angular state of the vapor can be destroyed by the applied magnetic field, lowering the optical saturation. When the Zeeman sublevels no longer overlap, the laser tends to oscillate with a transverse polarization of minimized saturation. Experimental evidence of these changes of polarization is given with an internal plane mirror laser on the 1.52 μm (J= 1 rightarrow J= 0) line of Ne²⁰. The observed data are pressure sensitive and give some information on the lifetime and disorienting cross section of the2s_{2}level of Ne.