Photoinduced changes in the optical constants of Ge-Se-AgI thin films

The photoinduced changes in the complex refractive index n = n - ik of thin films from the Ge-Se-AgI system with constant ratio Ge/Se = 1/4 and concentrations of AgI of 0, 5 and 10 mol% are studied by real time measurements of reflectance (R) and transmittance (T) of the films. The phase delay (delta) between the components of the transmitted wave, which is proportional to the birefringence of the film, is measured in real time as well. The changes in the average value of the refractive index (Delta n)- and in the average value of the absorption index (Delta k) in the imaginary part of n as well as the induced optical anisotropy are estimated by solving the inverse optical problem. It is found that involving small quantities of AgI into a Ge-Se matrix increases the sensitivity of the films, but the anisotropic effects are comparatively weakly in them. The maximum values of changes in the average refractive index (Delta n = 0.025) and in the average absorption index (Delta k = -0.03) are obtained in the films, containing 5 and 10 mol% AgI, respectively. Considerable values of the photoinduced anisotropy - birefringence (Delta n(a), approximate to -0.002) and dichroism (Delta D approximate to 0.05, which corresponds to Delta k(a) approximate to 0.035) are observed in films without addition of AgI ("pure" Ge-Se film). (C) 2000 Elsevier Science B.V.. All rights reserved.