Method for producing low scatter, low loss, environmentally stable dielectric coatings

A method for coating a substrate with a dielectric coating material, comprising:

• providing a high vacuum chamber including a substrate carrier device, an electron beam gun, the substrate, an evaporant source of the dielectric coating material, a plasma beam neutralizer that produces a plurality of electrons and an ion gun producing positively charged particles along a longitudinal axis of the ion gun;
• positioning the plasma beam neutralizer adjacent to and in a lateral direction relative to the ion gun longitudinal axis;
• generating the plurality of electrons from the plasma beam neutralizer which mix with the positively charged particles along the longitudinal axis of the ion gun, producing a beam of flowing plasma;
• evaporating the dielectric coating material with the electron beam gun to form a dielectric coating material evaporant that is directed to the substrate;
• providing a momentum assist from the beam of flowing plasma to the dielectric coating material evaporant;
• and
• forming a dielectric optical coating on the substrate at a deposition rate less than or equal to about 2.3 Angstroms per second so the coating has a low optical loss of 100 ppm or less.