Optically trapped delayed elasticity in germanium selenide glass fibers

Abstract

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

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“…[ 45 ] It is a non‐thermal effect of photosoftening or photofluidity, a drastic decrease of the film viscosity in the illuminated area. [ 4,68 ] Photofluidity in non‐crystalline chalcogenides is related to an increasing mobility of a considerable fraction of atoms in the course of exciton self‐trapping and at their recombination. [ 69 ] Photoassisted processes and thermally activated processes can independently result in a decrease of the material viscosity.…”

“…[ 69 ] Photoassisted processes and thermally activated processes can independently result in a decrease of the material viscosity. [ 68 ] At sufficiently high photoelectronic excitation, in the photofluidic state, the role of so‐called optical forces, [ 70 ] first of all, of an intensity gradient force, [ 71 ] will increase. This force initiates the photoinduced transfer of the film material from intensely illuminated towards less illuminated areas.…”