Why does the PVD coating shows color?

- May 29, 2019-

Why does the PVD coating shows color?


Why are there so many colors? This has to be analyzed from the purpose of coating.
Both glasses and lenses want to let as much light as they need in the desired wavelength (that is, light of certain colors) pass through as much as possible. However, about 5 percent of the light entering different transfer materials, such as air into the glass, is reflected off. In an optical scope, there are many lenses and refractors.The whole thing adds up to a 30 to 40 percent loss of incoming light.


These membranes are called "antireflection membranes" and, as the name suggests, can improve the transmission of light at certain wavelengths.


In detail, the color of a variety of coating mainly depends on the thickness.


Specifically, light whose wavelength and thickness d satisfy the above relation will not be reflected.
Then this part of the light won't get into our eyes, so we see the complementary colors. For example, if we eliminate the green light, the lens we see will be red.

Complementary color ring:


Lenses coated with a single layer of opaque film are usually blue-purple or red, while lenses coated with multiple layers of opaque film are pale green or dark purple.
The purpose of coating multilayer film is to use the above formula to further improve the transmission, in addition, the purpose is not only to improve the transparency, as shown in the figure below is the coating on the resin lens, the coating on the lens from bottom to top is the lens plus hard film, connection layer, multilayer anti-reflection film, water film.


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