Optical Second-Harmonic Generation in Gases: "Rotation" of Quadrupole Moment in Magnetic Field

Abstract
We report optical second-harmonic generation in gases in a transverse dc magnetic field. An electric quadrupole moment of sodium or calcium vapor is induced by a two photon transition. The effect of the magnetic field is to transform the wave function within both the ground and the excited magnetic sublevels, and to make a new component of the quadrupole moment which can generate a collinear second harmonic. Transverse magnetization is not important in the present case.