A method for polishing the surface of a diamond film with a low power density plasma in a reactor which comprises disposing O2 gas and a fluorinated gas such as SF6, NF3, and C2F6 in the reactor, providing power to the reactor so that the power density in the reactor is between about 1.0 watts / cm2 and about 1.1 watts / cm2 for a first duration, and maintaining temperature in the reactor at between about 200 DEG to about 400 DEG . The method may alternatively comprise disposing a sputter gas such as Ar,O2 or N2 in the reactor, providing power to the reactor so that the power density in the reactor is between about 3.0 watts / cm2 and about 7.5 watts / cm2 for a first duration, and performing a sputter etch, disposing O2 gas and a fluorinated gas such as SF6, NF3, and C2F6 in the reactor, and providing power to the reactor so that the power density in the reactor is between about 1.5 watts / cm2 and about 3.0 watts / cm2 for a second duration.