The spectrum of optical emission from the plasma of hydrocarbon gases was measured with a photomultiplier and an optical multichannel analyzer in PBIID (plasma-based ion implantation and deposition) system. When negative pulsed voltage was applied to a sample, a strong optical emission was observed. It is important to know a contribution of negative pulsed voltage discharge on DLC (diamond-like carbon) synthesis. Spectra of CH (431 nm), H-alpha (656 nm), H-beta (486 nm) and H-gamma (434 nm) were observed. Deposition rate of DLC film using acetylene gas was almost proportional to intensity of CH spectrum. (c) 2005 Published by Elsevier B.V.