The derivative method of critical-angle refractometry for attenuating media

Specular reflectance of monochromatic linearly polarized light, reflected on the interface of a prism coupled to a transparent medium at the critical angle of the transition to total internal reflection, has been long utilized to accurately determine optical constants, such as the refractive index and the dielectric constant, by the so-called "derivative method". However, in its original formulation, the derivative method does not account for the imaginary part of the complex optical constants that chararacterize attenuating media and becomes increasingly inaccurate even for the real part when attenuation grows. We therefore devise a proper analytic extension of the derivative method for attenuating media. Reflectance and angle of incidence at the derivative maximum are the experimental input quantities that yield both parts of the complex dielectric constant for both linear polarizations.