Optical coating materials

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An optical coating is the application of one or more metallic (or dielectric), films to an optical part’s surface. A coating applied to the optical part’s surface is used to increase or decrease the intensity of the reflection, beam separation and color separation as well as filtering out light. The most common coating techniques are vacuum coat and electronicless coating.

Principle of optocoating:

Vacuum coating:

Vacuum coating refers to coatings that must be done in higher vacuums, such as vacuum ion, magnetron, magnetron, molecular beam epitaxy and PLD laser-sputtering. A substrate is formed from the plated materials and electroplated materials are used for target or medicinal purposes. The target and substrate are in the same vacuum.

The evaporation coating is usually the target of heating so that the surface components evaporate in the form of free radicals or ions and are deposited on the surface of the substrate by film-forming method (scattering island structure-trapezoidal structure-layered growth).

Sputtered coat

You can easily understand the process of sputtered coating. It involves bombarding the target material with electrons or high energy lasers. Finally, the surface components are sputtered under the form free radicals orions. This forms a thin film.

An optical film has a smooth top, a geometrically-segmented interface between layers, and a refractive Index that can jump at interfaces. But it’s continuous within the film. This can either be transparent or optical.

The absorption medium can be either uniformly normal or not. Practical application of the film can be more difficult than an ideal one. Because of its optical and physical characteristics, it is different from bulk material. Its surface and interface are also rough which causes diffuse scattering. Due to mutual penetration, the film forms a diffusion interfacing, which results in anisotropy.

Common optical coating materials include the following:

1. Metal (alloy): germanium, chromium, aluminum, silver, gold, etc.


This rare metal is safe and non-toxic. It has a light transmission range of 2000NM to 14000NM.


It is sometimes found in spectroscopes, and it’s usually used as “colloid” to increase adhesion. Although the limit of the colloid layer can be 550NM, under the guidance of aluminum mirror, 30NM is the most effective value for adhesion.


It is the most reflective metal in the ultraviolet area. Effective thickness is over 50NM.


When the substrate temperature and evaporation rate are low enough, silver will have the same high reflectivity of aluminum. This is because there is more absorption due to the massive accumulation that occurs at very low speed.


Material with highest reflectivity of all known materials is above infrared 100nm wavelength

2. Oxides.

Yttrium trioxide.

By electron gun evaporation the property of the material changes with film thickness. The refractive index, which is approximately 1., can be used. 8 % at 500nm. It’s very well-known as an aluminum protective coating, in particular due to its high incident angle at 800-12000nm.

Cerium dioxide.

High-density tungsten boat evaporates cerium dioxide on a substrate of 200°C to get a refractive Index of around 2.2. This absorption band is approximately 3000nm in length and its refractive index is affected by the substrate’s temperature. Oxygen ion plating can produce nylon 2.35 (500nm), which is a low absorption thin film.


The refractive Index is defined as the light transmission range between 2.21500 and 3.15000nm. People love this material because of its high refractive and relative firmness. It is used for anti-reflection films, splitter films, cold light films, filter, high reflective film, glasses film and thermal mirror.

Silicon dioxide.

It is a transparent colorless crystal with a high melting point and hardness. This gives it good chemical stability. Use it for high-quality Si02 coatings. It has a very pure crystal with no melting point. You can divide it into infrared, visible and ultraviolet depending on your use. A film with too much pressure can cause pores to form and be fragile. Conversely, a film with too little pressure will absorb more light and its refractive Index will rise.

Zirconium dioxide.

High refractive index, high resistance to temperature and chemical stability make the white heavy crystal very pure. You can use it for high quality zirconia coatings. Because of its roughness, the incident light will be diffused and the transmittance of your lens is reduced. Additionally, optical rotation will cause certain incident light sources to dissipate particularly strongly. One example is that a material which absorbs red light appears green. But, poor processing can still be avoided.

Hafnium oxide.

If the substrate is heated to 150C by an electron gun, its refractiveindex is approximately 2.0C. Oxygen ion assisted plating can achieve a stable refractiveindex of 2.5-2.1. In the region of 8000-12000NM, HFO2 works better than SiO2 for the protective outer layer.

3. Fluoride.

Magnesium fluoride.

This antireflective coating has a 1×4 wave thickness and is used widely as an optical glass. It transmits about 120NM true ultraviolet radiation to the middle-infrared region at about 7000nm.

Calcium fluoride or barium fluoride.

The only problem with their compactness is that they are not completely solid. They can be used only in infrared films because transmittance shifts to higher wavelengths at high temperatures.

Lead fluoride.

This material can also be used in UV. If it’s used at 300nm the refractive indice decreases when it gets in touch with molybdenum or tantalum. Therefore, platinum and ceramic dishes are required.

4. Additional compounds

Zinc sulfide.

Light transmission ranges with refractive indices of 2.35400-13000m have good durability and stress. Mainly used for spectroscopic and cold light films, decorative film, filters, high reflective film, and infrared films.

Lead Telluride.

It’s an IR material of high refractive. Because it’s a thin-film material, transparency is possible in between 300 and 4000 NM. The material is sublimated in the infrared. Substrat temperature is 250C. Prevention is essential. The maximum range of 40000NM is sufficient to make it work. Many other materials can be used to create a 14000NM edge.

Silicon dioxide Price

Price is affected by many things, such as the demand and supply in the market and industry trends. Economic activity. Unexpected events.

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Silicon dioxide Supplier

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