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What are the Different Types of Optical Thin Film Coatings?

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  • Written By: Mal Baxter
  • Edited By: Daniel Lindley
  • Last Modified Date: 14 September 2016
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The application of optical thin film coatings helps extend the capabilities of optics. These microscopically thin coatings reflect wavelengths of light in order to generate various optical responses. Transmissive properties may include anti-glare, polarizing filtering, band-pass filtering, electrical conductivity, abrasion resistance, and beam-splitting, among a number of other of technology-specific applications. These coatings are applied to optical surface substrate materials such as plastic, glass, infrared material, and metal.

Optical thin film coatings perform duty in a wide range of industries, from scientific research and telecommunication to semiconductors and aerospace. The applications are numerous. These coatings can appear in processes from the production of anti-glare windscreens on airplanes to the enhancement of laser communications and telescope reflectors.

The coatings are sometimes applied to their substrates in vacuums using electro-beam evaporation or resistive heat, ion-assisted or physical vacuum deposition. Certain methods better suit the intended performance of the film, which include density, toughness, or adhesive qualities, depending on specific requirements. Techniques pertaining to evaporation, thickness, ion sourcing, and automated technologies can assist in their production.

Anti-reflection and high reflection varieties represent the most common types of optical thin film coatings. Uncoated surfaces such as glass sometimes exhibit unwanted ghost images and reflections, which obstruct their performance. Anti-reflective coatings, such as “beam splitters," can be optimized for their respective technology or placement, for example, for predetermined wavelength or broadband ranges. In addition, usable light can increase proportionally to the decreased reflections.

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Mirror coatings cover optics from barcode and computer scanner mirrors to copiers and fax machines. These are sometimes characterized as “hot” and “cold” mirrors, that is, multilayered dielectric coatings that divide infrared heat from visible radiation, or light. This allows control over the proportions of heat or light radiated from a reflector. Dialectric coatings also function in high and low voltage applications, in ranges from direct current (DC) to radio frequencies (RF). Usually made of oxide ceramics or polymers, these types can be found in medical equipment such as high-temperature gauges and electro-surgical instruments.

Anti-reflective coatings serve military technologies. Conductive coatings can work as anti-static or implosion shields. Plasma coatings perform functions such as hardfacing, anodizing, bonding or electrocoating, in paper, rubber, and petrochemical industries.

In the specification of wavelengths, attenuation optical thin film coatings can perform other density changes for linear, circular, and radial functions. Dichroic and trichroic films separate out two or three colors respectively, as for lighting or entertainment effects. Light can be separated out in terms of visible, infrared, or ultraviolet spectra. These coatings can be optimized not only for wavelength but also technically specified angles and polarizations. Technology allows the application of these coatings and many others over countless surfaces. Optical thin film coatings assist in many industries beyond optics, promising new solutions to technical challenges and innovations.

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