The disclosure relates to microwave cavity plasma reactor (MCPR) apparatus and associated optical measurement system that enable microwave plasma assisted chemical vapor deposition (MPACVD) of a component such as diamond while measuring the local surface properties of the component while being grown. Related methods include deposition of the component, measurement of the local surface properties, and/or alteration of operating conditions during deposition in response to the local surface properties. As described in more detail below, the MCPR apparatus includes one or more electrically conductive, optically transparent regions forming part of the external boundary of its microwave chamber, thus permitting external optical interrogation of internal reactor conditions during deposition while providing a desired electrical microwave chamber to maintain selected microwave excitation modes therein.