The mirrors are given optical coatings which determine their reflective properties.

Unwanted reflections can be reduced by the use of an anti-reflection optical coating.

"What I want to know is where their optical coatings came from."

So there was still a problem with the optical coating, after all.

Instead of a metallic coating, a dielectric optical coating may be used.

Multiple layers of different materials can be used, for example to form optical coatings.

Thin films are used to create optical coatings.

The inner layer is treated with a selective optical coating that absorbs energy without reflection.

In these cases, rather than using separate mirrors, a reflective optical coating may be directly applied to the laser medium itself.

A lot of optical coatings, thermal and insulating substances.