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.

• Received 9 February 1977

DOI:https://doi.org/10.1103/PhysRevLett.38.894