Composition dependence and reversibility of photoinduced refractive index changes in chalcogenide glass

International audiencePhotoinduced refractive index changes are investigated as a function of composition in Ge-As-Se chalcogenide glass by measuring the formation of Bragg reflectors photo-imprinted in polished glass discs. It is shown that the glass network connectivity has a strong effect on the photostructural changes which decrease dramatically when the rigidity percolates through the structure at coordination numbers langrrang > 2.4. The Bragg reflector formation is also affected by the refractive index of the glass which varies sharply with langrrang and correlates directly with the glass density. The photoinduced refractive index change is shown to reverse upon annealing near the glass transition following a non-exponential kinetic that closely matches the kinetics of structural enthalpy relaxation. The Bragg reflectors can also be reversibly erased and readjusted to a new wavelength through subsequent irradiation with a different photon energy. The composition dependence of photosensitivity is discussed in terms of structural constraints. It is suggested that over-constrained networks remain rigid despite photoexcitation of bond constraints therefore precluding photostructural rearrangements