Robert B. Hallock

Bulk diamond for IR/rf windows and domes

Microwave plasma deposition techniques for preparing optical quality, uniformly thick diamond plates and domes continue to be actively developed. Thicknesses greater than two millimeters have been demonstrated for optical quality dome blanks, and excellent optical quality has been obtained for five inch diameter plates. Presently achievable CVD diamond is the strongest LWIR-transparent material and is impervious to thermal shock. It can be used in its present form for prototype window preparation. Nevertheless, further strength improvement is required for CVD diamond for applications requiring resistance to particle (e.g. raindrop) impacts. Fracture strength improvement is a primary objective of diamond technology development. Continued development of optical diamond technology must also emphasize increased deposition rates for the highest quality material and optimized polishing processes to assure its place as a cost effective optical material for high performance applications.

Diamond-coated ZnS for improved erosion resistance

Durable coatings are used to improve the erosion resistance of high performance optical materials such ZnS. Diamond is the hardest and stiffest of all LWIR transparent materials and would make an excellent protective coating for ZnS. Direct deposition of diamond on ZnS by microwave plasma CVD has proved to be very difficult. Atomic hydrogen used in the diamond deposition process attacks and destroys ZnS very rapidly. In order to protect ZnS during the diamond deposition process protective IR transparent interlayers were developed. These layers encapsulate the ZnS and provide a nucleating surface for diamond deposition. Two different methods of nucleating diamond on these interlayers were developed to produce fully dense diamond films several microns thick. The sand erosion resistance of diamond coated ZnS was found to improve when the diamond was deposited on patterned ZnS substrates.