Structure-optical property correlations of arsenic sulfide glasses in visible, infrared, and sub-millimeter regions

Optical properties and structural aspects of As_xS _100-x glasses from visible to terahertz wavelengths were explored. A series of annealed, bulk As_xS_100-x glasses (x=30 to 42) were made and their refractive indices determined at terahertz, infrared, and visible frequencies using a quasi-optical backwards wave oscillator spectrometer for terahertz measurements combined with a prism coupler for visible and infrared measurements. It was found that the refractive index at all frequencies increases with arsenic composition up to 40at.% arsenic and then decreases with additional arsenic. The structure in X-ray diffraction patterns supports the notion of a minimum volume at 40 at.%, while the average covalent coordination number indicates that the rigidity percolation threshold is reached there. At arsenic concentrations >40 at.%, the network becomes over-constrained, and the molar volume increases.