Optical transmission through ferroelectric thin films as a probe of surface terms

A general formulation of the optics of ferroelectric films can be based on the Landau-Devonshire expansion together with the Landau-Khalatnikov dynami cal equations. We discuss in detail the implications for optical (far-infra red) transmission through a ferroelectric film. Because of the term D(del P )(2) that is allowed in the free energy density two optical waves +/-k(1) a nd +/-k(2) propagate in both up and down direction in the film even for nor mally incident radiation. The amplitudes of these waves together with the r eflected and transmitted amplitudes are determined from the electromagnetic boundary conditions together with a boundary condition on P of the form dP /dz+/-delta(-1)=0. It is shown that Fabry-Perot type fringes related to bot h k(1) and k(2) are seen. Calculated reflection curves are shown to illustr ate the extent to which optical measurements can be used to find the previo usly ill-determined parameters D and delta.