Figure shows the evolution of the experimental observables (Is, Ic) versus wavelength over a range extending from 2100 nm to 190 nm (0.6eV to 6.5eV). The oscillations of these observables are known as interference fringes and indicate that the material is transparent across the measured range. The amplitude of the fringes shows a decay below λ = 400 nm. This is due to the increase of the absorption in this range.