This work presents a laser desorption study of Ga5Ge20Sb10S65 chalcogenide glasses. The desorption products have been analyzed by UV multi-photon ionization and time-of-flight mass spectrometry. Desorption mechanisms and plume dynamics have been investigated by studying the desorption products velocity distribution profiles in the frame of a Knudsen layer model. A peculiar behavior (broadening of the mass spectral lines) of the Ga component was found at high desorption-ionization delays and a tentative explanation has been proposed, based on the very different thermal properties of the sample constituents. (c) 2005 Elsevier B.V. All rights reserved.