Optical coating materials

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An optical coating is the application of one (or several) 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, color, and polarization. Two common methods of coating optical parts are vacuum coating, and electronic 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 electroplated materials and then the target, or medicine material, is applied to it. 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 interface. But, it’s continuous within the film.

The absorption medium can either be uniformly normal or not. Practical application is much more difficult than an ideal film because of its optical and physical characteristics. Its surface and interface can be rough which causes diffuse scattering. Due to mutual penetration, the films form a diffusion interface. The anisotroy is formed by the growth, structure, and stress of film.

Common optical coating materials include the following:
1. Metal (alloy): germanium, chromium, aluminum, silver, gold, etc.
This rare metal is safe and non-radioactive. It has a light transmission range of 2000NM to 14000NM.

Used in spectroscopes, sometimes as a “colloid” layer to improve adhesion. It may range from 550NM to 30NM. But, under the guidance of aluminum mirror, 30NM can be an effective value to boost 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 high 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 500 nm. It’s very well-known as an aluminum protective coating, in particular due to its high incidence angle at 800-12000nm.

Cerium dioxide.
High-density tungsten boat evaporated cerium dioxide on 200°C substrate. This gives a refractive indice of around 2.2. It’s possible to change the substrate temperature by changing its absorption bands. Oxygen ion plating can produce nylon 2.35 (500nm). These thin films have low absorption.

Refractive index measures the light transmission range between 2.21500 and 3.0500 nm. People love this material because of its high refractive and relative firmness. It is used for anti-reflection films, splitter films, cold light films, filters, high reflection films, glasses film, thermal mirror, and other purposes.

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

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 lens will reflect more light than usual and diffuse the incident light. 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 refractiveindex is evaporated at 150C by using an electron gun, then it should be around 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 towards longer wavelengths at high temperature.

Fluoride with lead.
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 to make spectroscopic and cold light films, decorative films, filters, high reflective films, and infrared movies.

Lead Telluride.
It’s an IR material of high refractive. Because it’s a thin-film material, transparency is possible in between 300 and 4000NM. 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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