New difference reflectance methods for study of small interfacial effects.

Two sensitive differential optical techniques useful for study of small reflectance or absorptive differences between two interfaces are described. The first scheme employs a mechanically chopped light beam impinging on an arrangement of symmetrical dual cells to allow detection of differential reflectances DeltaR/R<10(-3). The second is a polarization-modulated beam-split laser version of the same method yielding approximately the same sensitivity. Representative measurements of voltage-induced reflectance changes at liquid-solid interfaces using these methods are given.