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Magnetoelectric Phenomena in Nonlinear Optics

Theoretical aspects and experimental observations of nonlinear magnetoelectric phenomena concerning the optical second harmonic generation are discussed. The coexistence of ferroelectric and antiferromagnetic orders in the hexagonal manganites R MnO 3 leads to a new contribution to the nonlinear polarisation. Polarisation selection rules of this contribution allow to determine the magnetic space groups of the hexagonal manganites. Spectroscopic study of second harmonic generation in magnetoelectric garnet films reveals the role of bismuth substitution in these compounds. A new magnetic-dipole mechanism based on magnetoelectric excitation of second harmonic generation in the centrosymmetric antiferromagnet NiO is experimentally studied. Multiphoton resonance gives rise to a high efficiency of this mechanism in NiO.