A low‐temperature (≊400 °C) plasma‐enhanced chemical vapor deposition process has been developed to grow diamond films for optical coatings application. Films with fine grains (≤3000 A˚) have been obtained by controlling diamond nucleation. The surface roughness of the films is on the order of 50–200 A˚. The optical transparency of the films is over 60% in the range 0.6–2 &mgr;m wavelength, which is comparable to that of Type IIa natural diamond. Using a block‐on ring tribotester, it is found that the diamond films adhere well to quartz substrates.