Second optical harmonic generation as a probe for magnetoelectric properties of multiferroic BiFeO 3

Based on the theoretical symmetry analysis of the nonlinear electric susceptibility, second harmonic generation is examined as a probe for detection of various type of ordering: magnetic, ferroelectric, ferroelastic. The nonlinear optical response of multiferroics is illustrated by the example of bismuth ferrite BiFeO₃. It is shown that magnetically induced second harmonic response as well as anisotropic part of ferroelectrically induced second harmonic depends on mechanical (ferroelastic) ordering. This is one of the aspects of order parameters coupling in multiferroics.