Abstract: A process for depositing diamond on a substrate using a microwave plasma generator including providing carbon, hydrogen and oxygen in a desired ratio to the microwave plasma generator, and providing sufficient microwave power to the microwave plasma generator to produce a greenish-colored plasma with the C.sub.2 emission at 5165 Angstroms (.ANG.) at a level of from 0.5 to 50 times the atomic hydrogen alpha emission level at 6563 .ANG., for depositing high quality diamond at an extremely high rate on the substrate placed proximate or in the plasma.