Mechanisms of the refractive index change in DO11/PMMA due to photodegradation

Using a white light interferometric microscope (WLIM) we measure the photodamage induced change in the complex index of refraction of disperse orange 11 (DO11) dye-doped (poly)methyl-methacrylate. We find that the change in the imaginary part of the refractive index is consistent with previous measurements of photodamage-induced absorbance change. Additionally, we find that the irreversible change in the real refractive index can be separated into a component due to damage to the dye molecules and a component due to irreversible damage to the polymer. From the features of the polymers contribution to the irreversible change in the real refractive index we conclude that photo-thermal induced chain scission and cross linking are the underlying mechanisms of polymer damage.