Relief surface formation as a result of light irradiation is one important property of chalcogenide glasses which gives rise of number of applications. Understanding the nature of the process is an essential step towards optimization of the relief images obtained. This work depicts the mechanisms for surface relief grating formation in Ge-Se thin films exposed to diffracted light. A dependence on the period of the illumination source is revealed, which correlates with the composition of the thin film material. Raman spectroscopy, Energy Dispersive Spectroscopy (EDS), and Atomic Force Microscopy (AFM) were used to analyze the films. The results point towards a dual effect of light irradiation leading to mass transport and structural changes, which results in a surface relief formation. Copyright © VBRI Press.