Expressions for determination of layer absorbances of a weakly absorbing double-layer sample through reflectance at the Brewster angles

A new technique for determining absorbances of interferenceless (incoherent) layers based on measurements of the ratio of the front and the back reflectivities of a double-layer sample at the Brewster angles is proposed. A double-layer stack must have at least one absorbing layer, and the two layers should be interferenceless and should be thicker than the wavelength of the incident light. We found that under these conditions the ratio of the front and the back reflectivities at the Brewster angle of a sample surface is directly related to layer absorbance. For a layer with a known thickness this means finding the extinction coefficient of the layer material. In comparison with the conventional method for measuring transmittance, the advantage of this approach is that it affords an opportunity to get rid of the influence of surface effects on the measuring volume absorption coefficient. For a thick layer with known thickness, it makes possible the determination of a small bulk absorption on a background with even greater surface effects. We trust that this technique will prove to be powerful for measuring the extinction coefficients of weakly absorbing materials.