The present invention relates to an improved method of depositing a diamond-like carbon film onto a substrate by low temperature plasma-enhanced chemical vapor deposition (PECVD) from a hydrocarbon/helium plasma. More specifically, the diamond-like carbon films of the present invention are deposited onto the substrate by employing acetylene which is heavily diluted with helium as the plasma gas. The films formed using the process of the present invention are characterized as being amorphous and having dielectric strengths comparable to those normally observed for diamond films. More importantly, however is that the films produced herein are thermally stable, optically transparent, absorbent in the ultraviolet range and hard thus making them extremely desirable for a wide variety of applications.