OPTICAL BIREFRINGENCE IN INHOMOGENEOUS POLAR LIQUIDS - EXISTENCE OF A NATURAL KERR EFFECT

We show that a polar liquid at a planar interface is spontaneously birefringent as a consequence of the image potential which creates an alignment of the molecules. For axially symmetric molecules this alignment induces an anisotropy of the refractive index. This effect can be calculated in various kinds of interfaces. Far from the centre of the interface we show that the birefringence is rigorously determined by the static Kerr constant in the bulk phase. This natural Kerr effect appears in ellipsometry measurements. We discuss the magnitude of this phenomena in the case of nitrobenzene. A new expression of the Kerr constant in homogeneous liquids is derived.