Advanced deposition technologies produce optical coatings with state-of- art-optical performance, improved durability, stability and lifetime and sometimes improved scalability to large optics and small-optics volume coating. This paper examines a low-energy, high-flux reactive ion assist process developed at Itek during the past four years from this perspective. The process is introduced at the fundamental level of ion and atom energetics and arrival ratios, with both inert and reactive gases. Earlier high-voltage, low-current approaches are contrasted. The manifold benefits of coating densification, improved stoichiometry, low-temperature processing and in situ substrate cleaning are described. Process implementation in mid-sized and large coating chambers is pictorially illustrated. Inexpensive retrofit is realized. Very low absorption, enhanced durability and precision mechanical stress control are demonstrated with selected highlights of recent Itek optical coating experiences. Examples of especially-interesting optics recently coated are shown. Competing coating technologies are compared.
The advantages of high current, low voltage ion assisted deposition (IAD) previously demonstrated for single layer films were extended to complex multilayer oxide coatings for medium to large scale applications. Optimization of the IAD parameters led to low absorptance coatings from the IR to the UV. Stress adjustment and matching of layers provided greater cohesive strength and mechanical integrity throughout the stacks. In addition near bulk indices gave enhanced optical performance. Examples of multilayer high reflector stacks for UV, visible, and near IR laser application are given with emphasis on absorption, optical performance in band, elimination of physisorbed water, and at the waterband, environmental stability, and coating durability.
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