Sensitivity of the reflection technique: optimum angles of incidence to determine the optical properties of materials

The purpose of this study is to develop a technique that will provide the maximum sensitivity of the reflection technique for the determination of the optical properties of materials. Analytical relations are presented that yield the maximum sensitivity of the technique for a given range of angles of incidence and refractive indices. The methods of the reflectance ratio at one and two angles of incidence are compared. The angular range of 75 degrees to 80 degrees was found to be suitable for the maximum sensitivity for the reflectance ratio at one angle of incidence, whereas for the two angles of incidence the ranges 45 degrees to 60 degrees and 75 degrees to 85 degrees are suitable. Furthermore, angular-reflectance measurements on a specular carbon-rod surface at the wavelength of 3.5 microm were used to demonstrate the advantages of inverting full-angularrange data as opposed to one or two angle measurements. The limitations of the measurements at normal incidence and 45 degrees are also assessed.