Theory of far infrared spectroscopy for ferroelectric size effects

We propose that far-infrared reflection and transmission measurements would be a sensitive probe of possible variations in the polarization P of a fer roelectric near a surface. We present a general formulation based on the La ndau-Devonshire model, including both linear and nonlinear processes. Surfa ce effects are described by parameters D, giving the free-energy cost of sp atial variations in P, and delta, governing the boundary condition on P. De tailed calculations for linear reflection in normal incidence from a semi-i nfinite medium are presented. If delta(-1) = 0 the calculations are analyti c and the results for this case serve as a check on the numerical calculati ons that are applied for general delta. Altogether, the results suggest tha t the effects of D and delta should be distinct and measurable.