Metal organic vapor deposition (MOCVD) is a well known method for preparing high quality and large area CuIn1-xGaxSe2 (CIGS) absorber layers. Some in-situ non-contact monitoring systems are needed when CIGS absorber layers are manufactured in industry. In this study, CuInSe2 (CIS) and CIGS thin films with different composition ratios, [Cu]/[In + Ga], were prepared by MOCVD using [Me2In(mu-SeMe)](2), hexafluoroacetylacetonate Cu(I) (3,3-dimethyl-1-butene), trimethyl gallium and dimethyle diselenide as the In-Se single source, Cu, Ga and Se precursors, respectively. The Raman shift spectra of the films with various composition ratios were analyzed to produce a basic algorithm that can determine the composition ratios of CIS and CIGS thin films indirectly. (c) 2011 Elsevier B.V. All rights reserved.