The first optical interference coatings were produced about 70 years ago. Since then, the optical coating industry has grown to serve a $2.1 billion market worldwide. There are three requirements to produce good multilayer optical interference coatings: 1. a good theoretical design; 2. at least two reliable coating materials; and 3. production processes which allow the deposition of these materials. A chart of historic milestones in the design of optical coatings was published before (An updated version of this chart is given below). In this paper we make an attempt to develop a similar chart of milestones in optical coating technology (harder, more stable and moisture resistant coating materials) and better production processes (more reliable, more precisely monitored, and allowing large area/high volume deposition).
The progress in the design of optical coatings is essentially connected with the invention of the needle optimization technique and with the accumulated experience of its practical implementation. These factors enable raising a question about the developing of an entirely automated optical coating design technique. The presented paper discusses difficulties of the formalization of the design problem and the ways to overcome the intrinsic uncertainty of its formulation. It formulates the basic principles of implementation of the entirely automated design technique and considers the main pro et contra of the push-button design technology.
The current two major non-numerical design methods, equivalent layers and polynomial synthesis, are reviewed and compared. The equivalent layer method works well when only a small number of fixed refractive indices is available. This is the case when the coating is manufactured by evaporation. Polynomial synthesis generates a priori better designs but does not allow predetermination of refractive indices. So, for evaporation, the designs have to be translated from many refractive indices to a few. This process generally downgrades the design. This translation is not necessary when sputtering or chemical vapor deposition is being used. Here, in-between refractive indices can easily be generated by mixing or flip-flopping. As a consequence, superior designs can be implemented.
The current two major non-numerical design methods, equivalent layers and polynomial synthesis, are reviewed and compared. The equivalent layer method works well when only a small number of fixed refractive indices is available. This is the case when the coating is manufactured by evaporation. Polynomial synthesis generates a priori better designs but does not allow predetermination of refractive indices. So, for evaporation, the designs have to be translated from many refractive indices to a few. This process generally downgrades the design. This translation is not necessary when sputtering or chemical vapor deposition is being used. Here, in-between refractive indices can easily be generated by mixing or flip-flopping. As a consequence, superior designs can be implemented.
The current two major non-numerica1 design methods equivalent layers and polynomial synthesis, are reviewed and compared. The equivalent layer method works well when only a small number of fixed refractive indices is available. This is the case when the coating is manufactured by evaporation. Polynomial synthesis generates a priori better designs but does not allow predetermination of refractive indices. So, for evaporation, the designs have to be translated from many refractive indices to a few. This process generally downgrades the design. This translation is not necessary when sputtering or chemical vapor deposition is being used. Here, in-between refractive indices can easily be generated by mixing or flip-flopping. As a consequence, superior designs can be implemented.
The two main synthesis methods of optical interference coating design, Epstein
equivalentlayersynthesis andChebyshevpolynomial synthesis, areevaluated, characterized and compared. Epstein designs are easier to produce. Chebyshev designs
are superior but, because of implementation problems, often turn out worse than
Epstein designs. This could change in 1 ight of recent progresses in rf-sputtering.
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