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Optical Coating

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1.The basic concept of optical coating

  • Definition of optical coating

Optical coating is the technique of depositing one or more thin layers of material on an optical element to change the way the optical element reflects and transmits light.

2.Type of optical coating

  • Reflective coating, such as high reflection film to manufacture polarized reflective film, color splitter film, cold light film and interference filter, common interference filter is divided into cutoff filter and band pass filter two categories, cutoff filter is generally known as edge filter, mainly long wave pass, short wave pass, dichroic mirror type.
  • Antireflective coating, products of this coating technology are often used on optical components with high transmittance requirements. In complex systems such as cameras, telescopes and microscopes, the reduction of reflection can also improve image contrast by eliminating stray light.

3.Traditional optical coating method

  • Vacuum thermal evaporation coating:
  • (1) Resistance evaporation source evaporation coating: can be used for coating materials with low melting point.But the heater life is short.
  • (2) Electron beam evaporation source evaporation coating: The high energy electrons emitted by the electron gun are bombarded on the surface of the coating material to vaporize the coating material with high melting point and high purity onto the substrate. In this process, ion-assisted deposition (IAD) can be used to accelerate the mobility of the particles that need to be deposited and increase the density of the film layer.
  • (3) High-frequency induction evaporation source evaporation coating: used for high-speed evaporation of coating materials, the evaporation device needs to be shielded, the use of high-frequency generators to complete.

4.Comparison of methods of optical coating technology

  • Evaporation deposition method, the solid coating material is heated, so that its surface evaporates, the evaporated particles will be moved to the target substrate after re-condensation.
  • Sputtering deposition method, the solid coating material is bombarded with high-energy particles such as plasma to produce particles on the surface, and these particles are sprayed on the target substrate for condensation.
  • Ion deposition method, evaporation of solid coating materials, the use of glow discharge to solidity the evaporated gas electrification on the substrate condensation, both evaporation and sputtering deposition characteristics.

What is the difference between evaporative deposition, sputtering deposition and ion deposition?

Evaporative deposition: Because the particles produced by sputtering deposition can damage the substrate surface, evaporative deposition can better control the deposition rate to precisely how many nanometers per second are deposited.
Sputtering deposition: It is very easy to gasification some metals with a high melting point, and for the heating of chemically stable materials, the sputtering deposition coating efficiency will be faster than the evaporation deposition coating efficiency.
Ion deposition: The resulting diffraction coating can make the film more dense.

5.Thin film deposition in optical coating

Two thin film coating methods:

  • Physical vapor deposition coating (PVD):PVD coating technology has many advantages, including high purity, good uniformity, strong adhesion, and adjustable film composition.
  • Chemical vapor deposition coating (CVD):Due to the chemical reaction that occurs in CVD coating, CVD has become the process basis for the preparation of new materials, while significantly reducing the temperature required for material molding, which is particularly advantageous for the preparation of high melting point materials.

What is the difference between physical vapor deposition and chemical vapor deposition?

First of all, the principle is a bunch of small gas molecules or atoms are concentrated on the surface of the target substrate, but the physical deposition only takes place physical reaction, that is, the coating material is gasification and evenly sprayed on the surface of the substrate, while chemical deposition takes place chemical changes, and one or several particles on the surface of the substrate will re-form a new substance, thus achieving a film that PVD cannot make. For example, graphene.

Optolong is a 20 years of experience on optical coating companies,The Full Width at Half Maximum of 3 nm is achieved at optical bandpass filter products by using PVD coating technology and IAD assisted coating technology.

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