Abstract: A rf plasma enhanced chemical vapor deposition process is presented, wherein a precursor gas stream having a high helium content produces hard, wear resistant, hermetically sealing, high refractive index Diamond-Like-Carbon (DLC) coatings on numerous substrates at deposition rates of at least 0.4 .mu.m/hr. Internal pressures of 1 to 10 Torr and radio frequencies no higher than 100 kHz are employed. The process may be applied to both batch and linear production methods. Linear products such as optical fibers, capillary tubing, wires, and sheets can be coated in-line while minimizing the introduction of flaws on their surfaces and minimizing exacerbation of any pre-existing flaws. The effects of surface flaws can be minimized further by introducing a helium etch of the substrate surface prior to exposure to the DLC coating precursor gas mixture.