Optical spectroscopy of a-As2Se3 under in situ laser irradiation

We report the first in situ dynamic measurements of the optical spectrum in the complete visible region of the electromagnetic spectrum to assess the kinetics of photodarkening in chalcogenide glass films. Only through such measurements, we find limitations of the commonly used Swanepoel method for determining the optical characteristics of such films. A negative change in the refractive index of a-As2Se3 films is observed at wavelengths longer than the wavelength of the inducing light beam. The observation of transmission spectrum as a function of time indicates that the photodarkening and photoexpansion have different origins.