Correlating structure with non-linear optical properties in xAs sub(40)Se sub(60).(1 - x)As sub(40)S sub(60) glasses

A series of xAs sub(40)Se sub(60).(100 - x)As sub(40)S sub(60) glasses, where x= 0, 25, 33, 50, 67, 75 and 100 mol% As sub(40)Se sub(60), has been studied using neutron and X-ray total scattering, Raman spectroscopy and super(77)Se MAS-NMR. The results are presented with measurements of non-linear refractive indices, n sub(2), and densities. There is no evidence for the formation of homopolar bonds in these glasses, but neutron correlation functions suggest that there is a non-random distribution of sulfur and selenium atoms in sulfur-rich glasses. The average number of sulfur atoms at a distance of 3-4 Aa from a selenium atom, n sub(SeS), deviates from a linear variation with x in glasses containing