Abstract: There is provided a system for the manufacture of a diamond film. A plasma generator generates a hydrogen atom containing plasma stream into which a hydrocarbon containing gas is fed. The plasma dissociates the hydrocarbon to carbon radicals and carbon which are deposited on a substrate where the carbon crystallizes to a diamond film. The efficiency of the system is increased by heating the hydrogen source gas prior to generation of the plasma. Other means to increase the effectiveness of the system include using a plurality of plasma streams and shaping the plasma stream, A low internal strain, high quality optical film is generated by depositing the carbon on a substrate supported by a heat sink having nonuniform thermal conductivity such that the thermal gradient across the surface of the heat sink is less than about 8.degree. C./centimeter.