Kinetics of holographic refractive-index gratings in rare-earth-sensitized glasses

Diffusion of small modifier cations over distances large compared to the interatomic spacing is used to account quantitatively for the kinetics of photoinduced refractive-index gratings that can be holographically written in rare-earth-doped glasses. A model is developed that includes diffusion activated by nonradiative relaxation of the rare-earth sensitizers, drift under the space-charge field or externally applied fields, and trapping of the mobile modifiers. In this model the refractive-index contrast of the grating arises from the modulation of the concentration of small modifiers. The model accounts well for experiments on Eu^3+-doped silicate glasses reported here.