Equipment for characterizing thin semi-transparent layers (1 nm to 5 mm). The system evaluates the thickness and the optical properties of the material (refractive index and extinction coefficient). The wavelength ranges from 380 nm to 780 nm or from 450 nm to 900 nm. The accuracy is 0.1 nm in layer width and 0.005% in the refractive index. The maximum dimensions of the samples are 200 mm x 4 mm or 200 mm x 400 mm.