Dependence of a giant optical nonlinearity of planaroriented nematics on the thickness of a sample

An analysis is made of the dependence of a giant optical nonlinearity of a nematic on the thickness of a sample L divided by the characteristic size a of a transverse inhomogeneity of the optical field. It is shown (and confirmed experimentally) that a nonlinear advance of the phase of light in a sample depends strongly and differently on L in the cases when L≪a and L≫a.