We wish to study a series of glasses of composition As2Ch3 (Ch = S, Se and Te) to investigate the effect of varying the chalcogen type on the non-linear optical (NLO) behaviour of the glass. Neutron diffraction data for twelve binary and ternary glass compositions and three crystals will be obtained. The results, used in conjunction with 77Se NMR, Raman, X-ray diffraction data (ISIS Ag-tube diffractometer), and Reverse Monte Carlo (RMC) modelling, will be used to develop structural models of these glasses. The variations in glass structure with composition will then be compared to measurements of the NLO response to improve our understanding of the relationship between the structure and physical properties of this glass system.