What is Optical Coating?

Optical coating refers to the process of coating a layer (or multiple layers) of metal (or dielectric) film on the surface of optical parts. The purpose of coating on the surface of optical parts is to meet the requirements of reducing or increasing light reflection, beam splitting, color separation, filtering, and polarization. Common coating methods are vacuum coating (a type of physical coating) and chemical coating. ^[1]

The coating is a layer of transparent electrolytic plating on the surface of the material by physical or chemical methods.

The interference of light is widely used in thin film optics. A common method of optical film technology is to apply a thin film on a glass substrate by means of vacuum sputtering, which is generally used to control the reflectivity and transmittance of the substrate to the incident light beam to meet different needs. In order to eliminate the reflection loss on the surface of optical parts and improve the imaging quality, one or more layers of transparent dielectric film are coated, which are called antireflection coatings or antireflection coatings. With the development of laser technology, there are different requirements for the reflectance and transmittance of the film layer, which has promoted the development of multilayer high-reflection films and broadband anti-reflection films. For various application needs, high-reflective films are used to make polarizing reflective films, color splitting films, cold-light films, and interference filters. ^[2]

The optical film is realized in a high-vacuum coating cavity. Conventional coating processes require elevated substrate temperatures (usually around 300 ° C); more advanced techniques such as ion-assisted deposition (IAD) can be performed at room temperature. The IAD process not only produces thin films with better physical properties than conventional coating processes, but also can be applied to substrates made of plastic.

We already know the transmittance and coating

There are several common optical coating materials:

1.Magnesium fluoride

Material characteristics: colorless tetragonal powder, high purity, using it to prepare optical coatings can improve the transmittance without breaking points.

2.Silica

Material characteristics: colorless transparent crystal, high melting point, high hardness, good chemical stability. It has high purity, and can be used to prepare high-quality Si0 ₂ coating film with good evaporation state and no collapse point. According to the requirements of use, it is divided into ultraviolet, infrared and visible light.

3.Zirconium oxide

Material characteristics White heavy crystalline state, with high refractive index and high temperature resistance, stable chemical properties and high purity. Use it to prepare high-quality zirconia coatings without breaking points ^[4]