Spurious electro-optic coefficients inferred from modulation ellipsometry measurements in the presence of an air cavity

Abstract This paper describes how thin air gaps in multilayer polymer thin film structures can lead to unexpectedly large signals in modulation ellipsometry experiments, which can then be misinterpreted as the electro-optic effect. The contributions from the electro-optic effect and polarisation on reflection from the air cavity are indistinguishable and the reflection contribution can be on the order of 100 times that of the electro-optic effect. Caution must thus be exercised in any attempt to measure electro-optic coefficients with modulation ellipsometry in the presence of air gaps, to avoid spuriously high results. Thin film multilayer structures containing air gaps may be suitable for some of the same applications as electro-optic reflectance modulators.