Second harmonic generation in the centrosymmetric antiferromagnet NiO - art. no. 137202

In spite of the fact that inversion is a symmetry operation of both the cry stalline and the magnetic lattice of NiO, second harmonic generation (SHG) has been observed below the Neel temperature. A spectroscopic study shows t hat the signal is due to combined magnetic-dipole and electric-dipole trans itions between the (3d)(8) levels of the Ni2+ ion in the crystal field. The SHG is resonant in both the incoming and the outgoing light waves and thus greatly enhanced. A quadratic coupling of the nonlinear polarization to th e order parameter was found. This allows the investigation of individual do mains.