Optical second harmonic generation in centrosymmetric antiferromagnetic NiO

Optical second harmonic generation (SHG) in NiO in spectroscopy and topography experiments reveals a pronounced signal below the Neel temperature which couples quadratically to the antiferromagnetic order parameter. The SH process originates in combined magnetic-dipole and electric-dipole transitions between the (3d)8 levels of the Ni2+ ion in the crystal field. It is greatly enhanced by being resonant both in the incoming and the outgoing light waves. The polarization dependence reveals a sensitivity of the SH process to both T and S domains which are investigated in imaging experiments.