Nonlinearity and photostructural changes in glassy As2S3 thin films

Measurements are reported of the refractive index and absorption coefficient changes of amorphous As2S3 (chalcogenide glass) thin films due to cw laser light irradiation. We have measured the transmittance through a thin film in the Z-scan technique configuration. Two different contributions to refractive index changes are demonstrated, showing the existence of a permanent and a dynamical effect. The first effect was demonstrated performing usual normal incidence transmittance measurements. The second dynamical change, revealed by the Z-scan technique, disappears once the light source is turned off: measured in the latter case is a maximum change of the refractive index Δn=-8×10-3 in the cw regime at λ=514.5 nm.