Optical coating

Abstract

A process for coating the surface of a material with a carbonaceous coating by vacuum deposition derives the carbon in substantially pure form from a hydrocarbon gas plasma, the surface to be coated being coupled to an A.C. power source operating at a frequency below 500 kHz at which the electrical impedance of the plasma is substantially non-varying during the deposition process. Because the plasma impedance is substantially constant the process is safe and reproducible and can be carried out without dynamic monitoring and adjustment procedures and there is no requirement for an impedance matching network between the A.C. power supply and the vacuum chamber. Frequencies in the range 300-400 kHz with applied voltages of the order of 1KV or greater have been found to give good results.

Dependencies are inferred from the claim text.