Refractive index of colored films of molybdenum trioxide

We apply a film thickness-independent technique to measure the index of ref raction n=n+ik for amorphous thin films of molybdenum trioxide. The films w ere grown by thermal evaporation and then colored by light irradiation for different exposure times. Data for the reflectivity and differential reflec tivity yield n and show no dependence on the density of color centers. We f ind that small variations of the absorption coefficient induce changes in t he differential reflectance line shape at angles different from the Brewste r angle. (C) 2000 American Institute of Physics. [S0021-8979(00)01413- 4].