Chalcogenide glasses undergo viscosity decrease under light irradiation ("photofluidity"). This effect has been known and investigated for many years now. Nevertheless, what is less well known, is that light irradiation impacts the whole viscoelastic behavior, and especially the delayed elasticity (or "anelasticity"). We investigate here the impact of light irradiation on delayed elastic recovery and compare it to the effect of temperature jumps. We show that photoinduced processes behind the photofluidity superimpose over the "natural" thermally activated processes. They produce their own contribution to the delayed elastic deformation without disturbing, or being disturbed, by the thermally activated processes. This contribution can be trapped by stopping the irradiation.Additionally, this trapping opens new routes to investigate photofluidity, by separating the photoinduced from the thermally activated processes. According to the experimental results, we also specify here the modified equations of linear viscoelasticity giving the evolution of the deformation during cycles of light irradiation.
K E Y W O R D Schalcogenide glasses, delayed elasticity, photoinduced fluidity, recovery, viscoelasticity
International audiencePhotoinduced changes in the mechanical properties of Ge-Se chalcogenide glasses produced by sub-band gap energy are studied by microindentation. The results show that the irradiation leads to an increase of the mechanical properties exactly module of Young and the hardness with a decrease of the viscosity in the case of the low intensities laser and a decrease of the mechanical properties with an increase of the viscosity in the case of the high intensities of irradiation
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