Diamond like nanocomposite film is grown using PECVD method for its use as IR window. It is seen that the argon flow rate variation can change the surface quality and the film thickness and these changes are also not linear. So, depending upon application, argon flow rate is to be optimized. Moreover, an interferometric technique to measure the phase variation of the film surface has been proposed. This phase variation is comparable with the surface quality as obtained from AFM images and can thus be considered as a cheap alternative technique to measure surface quality. © 2013 Elsevier GmbH. All rights reserved.