Nonlinear optical anisotropy associated with polar ordering in ferroelectric liquid crystals

We have developed a new experimental method of measuring the second harmonic generation (SHG) from ferroelectric liquid crystals (FLCs). The measurements are made on a homogeneously aligned FLC cell at an oblique incidence to the surface normal as a function of the azimuthal angle of rotation. This method is simple and powerful to study both the molecular orientation and the associated nonlinear optical (NLO) properties of FLCs. The absolute values of the NLO coefficients are determined self-consistently from both the SHG intensity profiles and the Maker fringes obtained for the same FLC cell. The anomaly observed in the electric field dependence is described in terms of the third-order optical nonlinearity of FLCs.