Thin films of silicon nitride were prepared by laser induced chemical vapor deposition (LCVD). During laser irradiation, photoluminescence was observed in the gas phase. The photochemical reactions involved were studied by measuring the accompanying photoluminescence (PL) signal at the wavelengths range between 350 and 800 nm. The PL measurements were carried out both for a pure ammonia gas and for a SiH4/NH3 gas mixture. During the deposition process NH2 was detected as the major dissociation product whose rate of production determined the deposition rate of the silicon nitride film. The correlation between the PL signal, the molecular composition in the gas phase and growth kinetics of the LCVD films is discussed. (C) 2002 Published by Elsevier Science B.V.