Fluctuation mechanism of doubling the frequency of optical radiation in liquid crystals

A new mechanism is suggested for phase-matched second harmonic generation using the quadrupole nonlinearity of a liquid crystal and resulting from an anomalously strong scattering of light by fluctuations of molecular orientation. An analysis is made of the structure of the tensors representing the regular and fluctuation-induced nonlinear susceptibilities and a calculation is reported of the relative efficiency of the fluctuation mechanism, which is estimated to reach a few percent.