The third-rank susceptibility tensor that describes the second-harmonic generation changed sign after an inversion operation indicating its sensitivity to twinning structures. Here, the far-field scattering patterns of second-harmonic radiation generated by single twinned and twin-free ZnO rods were shown. The patterns were successfully correlated with the twinning structures. A finite dipole-wire model was effectively employed to model the pattern. It indicated that the dark or bright fringes at the 0° scattering angle originated as a result of the destructive or constructive interference of spin-Hamiltonian waves emitted from each halves of the twinned or twin-free ZnO rod.

Far-Field Second-Harmonic Fingerprint of Twinning in Single ZnO Rods. Liu, S.W., Zhou, H.J., Ricca, A., Tian, R., Xiao, M.: Physical Review B, 2008, 77[11], 113311