Optical coating

Alter reflectivity and transmission with optical coating

An optical coating is one or more thin layers of a variety of materials, deposited onto an optical surface (such as a lens or mirror) in order to enhance or alter the transmission or reflection of light. Optical coatings are used for anti-reflection, high reflection, to dissipate static charge, or to filter light at certain wavelengths. The “optical components” on which optical coatings are applied include glasses, lenses, microscopes, mirrors (such as two-way mirrors), medical devices, lasers, and other high-performance optical machinery. Optical coatings are also used to prevent the build-up of static electricity in components.

The theory behind optical coating

Optical coating can alter reflectance and transmission of light.

Light reflected at different wavelengths appears to us as different colors.

How an optical coating performs depends upon the composition of the layers, the number of layers, the thickness of each layer, and the refractive index difference at the layer interfaces. Essentially, light behaves in very particular ways in different materials, and by carefully manipulating the composition, thickness, and number of layers, the light can be made to reflect, refract, only reflect the blue spectrum, or reflects and transmits a specific percentage of light. The refractive index of a material relates to how light propagates through that material, or how it bends (or refracts) when it is transmitted through it.

Mirror surfaces are the simplest of optical coatings, only needing the deposition of thin layers of metal (such as aluminum or silver) on glass. Anti-reflection coatings use materials known as dielectric. Each layer of dielectric material causes the light to change its angle, and the result is interference which reduces reflection, and the surface becomes anti-reflective. This method can also be utilized to create substrates which reflect or transmit on certain wavelengths. Dielectric materials include magnesium fluoride, calcium fluoride and some metal oxides.

How optical coatings are applied

There are several methods of applying an optical coating. These include:

  • Evaporative Deposition – using a vacuum chamber, the coating material is vaporized and the resulting vapor condenses on the substrate to be coated.
  • Ion-Beam Sputtering – like the evaporative deposition, the material is vaporized in order to corm on the substrate. However, in this case a beam of ions is shot at the substrate as well, in order to increase the adhesion an density of the coating.
  • Plasma Sputtering – this method uses the same principle as ion-beam sputtering, but the ions are not from a gun but from plasma.
  • Atomic Layer Deposition – here the material for the coating is in the form of a gas.

The process is labor, capital, and time intensive.

How much does optical coating cost?

Given all that is involved in optical coating, calculating cost relies on a number of factors. These include the number of components being coated, the type of optical component, the size of component, the number of layers needed for the coating, the number of surfaces to be coated per component, and which deposition process is needed for the coating application. Components also require preparation prior to coating.

There are several companies across the US that provide optical coating application and component services. These companies service the aerospace, medical, semiconductor, specialty lighting, industrial, and telecommunications sectors. If you would like any more information about optical coatings or American optical coatings manufacturers and companies, please contact us! A small selection of these companies is below:

  • Edmund Optics
  • Thorlabs
  • Syntec Optics
  • Optiforms
  • REO Precision Optical Solutions
  • ZYGO Corporation
  • Cascade Optical Corporation
  • Alluxa
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