This paper deals with the structure and the optical properties of thin
As40S60 − xSex
films doped with silver. The refractive index
n and the optical
band gap Egopt
were calculated from the transmittance and reflectance spectra. The results showed that
the photo-doping leads to increase in the refractive index by about 0.25–0.27. An effect of
thickness expansion was observed in the photo-doped layers. The non-linear refractive index,
γ, and the two-photon
absorption coefficient, β, were evaluated by applying a formula developed by Sheik-Bahae. Each of the films studied
exhibits a highly non-linear refractive index at the telecommunication wavelength, 70–850
times higher than that measured for fused silica. From the Raman spectra of thin
As40S30Se30
it might be concluded that under dissolution, the silver interacts with both sulfur
and selenium. The surface of the thin films was investigated by using a white
light interferometric profiler. It was found that the increase in the thickness of
the silver layer results in roughening of the surface of the photo-doped films.
The optical properties of single layers from As2Se3 and GeS2, double-layered stack and quarter-wave multilayer structure consisting of alternating layers from both materials are investigated. For modelling of multilayer coating the thickness dependence of the refractive index of single coatings from both materials is studied. The particularities and scope of application of different spectrophotometric methods for calculation of optical parameters of thin chalcogenide layers are discussed for film thickness, d, in the range λ/25–1.5λ (λ being the operating wavelength). Having acquired the knowledge of optical parameters (refractive index, n, and extinction coefficient, k) of the single layers, we designed and produced a one-dimensional photonic crystal with fundamental reflection band at λ = 850 nm. It was shown that the photoinduced changes of the refractive index of thin chalcogenide films can be used for enhancement of the optical contrast of both materials.
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