The kinetics of photo-induced dichroism in thin films of amorphous arsenic triselenide

We have measured the dichroism in amorphous As2Se3 films induced by a polarized pump beam of near bandgap light. The total induced dichroism saturates at a value that depends linearly on sample thickness—the relative change in the absorption coefficient is about 0.2%. We fit the time dependence of the induced dichroism to a stretched exponential function of the form exp(-(t/τ)β) and find that the time constant (τ) depends inversely on the pump-beam intensity and the stretching exponent (β) is in the range 0.5–0.6 depending on thickness but relatively independent of the intensity. A dc electric field had no effect on the induced dichroism. The addition of a small amount of iodine (0.1%) increased τ in some but not all samples.