A. Popescu, D. Savastru, S. Miclos, Refractive index anisotropy in non-crystalline As2S3 films, J. Optoelectron. Adv. Mater., 12/5 (2010) 1012 - 1018.
Title: Refractive index anisotropy in non-crystalline As2S3 films
Abstract: The refractive index in As(2)S(3) non-crystalline thin films was investigated by modified m-line spectroscopy waveguide method. In order to get a higher accuracy of about 10(-3) the experiment was done by using a second prism and assuring a waveguide modes coupling as weak as possible. This method has permitted to find out considerable optical anisotropy of 20.10(-3) in thin amorphous films. It was found that the anisotropy diminishes in thicker films and as a result of illumination with Ar laser irradiation. These results support the stratified model of the glass matrix and photoinduced fluidity phenomenon in non-crystalline As(2)S(3) films. New simple method to measure the refractive index of films in a spectral interval of film transparency was developed. The formula for calculation of film and substrate refractive indices was developed by measuring the normal optical transmission extremes of the interference fringes only. The method permits measurement of the refractive indices in both cases: the substrate refractive index is greater or less then the film refractive index. For the wavelength interval from 0.80 mu m to 0.85 mu m deviation from usual dispersive curve was revealed this could be related to some additional optical absorption at these energies. Dispersion curve suffers an upper shift after irradiation with Ar laser, this evidencing a meaning transition to a new denser structure. However dynamics of refractive index modification is quite different: faster for energies close to the band gap energies (lambda=0.65 mu m) and more slowly for energies close to the mid gap (lambda=1.0 mu m). This fact suggests the role played by preliminary electronic states excitation prior to structural transformation.
Key words: Optical spectroscopy; Chalcogenide films; Refractive index; Film anisotropy; Planar waveguide; Optical measurements