Detailed SVC Course Syllabus

C-104 An Introduction to Optical Coatings

No modern optical instrument could function without its optical coatings. Optical coatings assure the optical properties of the various surfaces that shape and manipulate the light. They consist of an assembly of materials in the form of very thin films that operate by a mixture of material properties and interference to yield the desired behavior. Optical coatings can eliminate reflection losses, separate wavelength regions, select or reject narrow spectral bands, manipulate polarization, compress optical pulses, or even play a purely decorative role.

Based on their optical behavior, the materials for optical coatings can be divided into two groups, dielectrics, including semiconductors, and metals. Dielectrics (and semiconductors) are essentially transparent in their useful spectral regions while metals are opaque. We can exploit these differences in behavior in the design of optical coatings in two major classes, those made entirely of dielectric material and those where both dielectric and metallic materials are used.

Accurate calculations of coating properties are so involved that computers are invariable used for any detailed calculation and for design. Computers, however, have no understanding of coating design nor any instinct for the correctness of a result. For this necessary capability we must rely on our own understanding and instinct, and there are many simple tools that help in this.

Since the performance of an optical coating is derived from interference effects, an appreciation of coating performance, and especially its limitations, relies on an understanding of interference and of the relevant material properties.

The manufacture of optical coatings is most frequently by a vacuum deposition process. As a result the films exhibit a microstructure typical of such processes that has a considerable influence on their properties, especially stability, environmental resistance, adhesion and the like.

This course is a one-day introduction to optical coatings, their design, manufacture, and behavior, taught at a fundamental level and without computers. A knowledge of basic principles is the key to solving even complex and involved problems. Why are metals better for some coatings than dielectrics? How many layers are needed for high reflectance? How is it that adhesive tape can stick better than an optical coating even though it has a poorer adhesive force? Why do coating properties drift after manufacture? Why is it difficult to find high-index materials for the ultraviolet? Why does coating performance vary with angle of incidence? The material covered in this course should make answers to these and similar questions immediately clear.

The level of the course is suitable for those new to the field, those who want a quick refresher, or those with experience who would like to fit it into an ordered framework. Advanced mathematics is definitely not required.

Instructor: H. Angus Macleod, Thin Film Center, Inc.