Challenges of developing hemispherical ZnS domes coated with a durable anti-reflection coating

摘要

The design of a modern optical system often raises new challenges for manufacturers of high end optical components. One such challenge, which has become more and more common, is the requirement for highly durable hemispherical domes to allow for wide field of view. There are many difficulties to overcome before the final product can be made. In this paper we present some of the major difficulties of developing such domes made from ZnS grown by chemical vapor deposition (CVD). First, the CVD process which introduces the challenge of removing the grown raw dome from the graphite mold without causing cracking and breakage is discussed. Then, the challenges introduced by the electron beam (EB)-gun evaporation method, most commonly used for evaporating the anti-reflection coating, are presented. Amongst these challenges, the mounting of the dome in-side the coating chamber, the coating uniformity over the dome's curvature and the coating's environmental durability are the most difficult problems to overcome. The paper presents how computerized modeling along with experimental procedures can be combined to minimize the difficulties in the production processes and improve the overall product quality and yield.