Optical coating technology

Release time:

2023-08-15

1. Evaporative deposition
During evaporative deposition, the source material in the vacuum chamber evaporates due to heating or electron beam bombardment. Vapors condense on optical surfaces. During evaporation, uniform optical coatings with specific thicknesses can be manufactured by precisely controlling heating, vacuum pressure, substrate positioning, and rotation.
Evaporation has a relatively mild nature and can cause the coating to become loose or porous. This loose coating has water absorption, which changes the effective refractive index of the film layer and leads to a decrease in performance. Ion beam assisted deposition technology can enhance evaporation coating, during which the ion beam aligns with the substrate surface. This increases the adhesion of the source material to the optical surface, generating more stress, making the coating denser and more durable.

2. Ion beam sputtering (IBS)
In ion beam sputtering (IBS), a high-energy electric field can accelerate the ion beam. This acceleration gives ions significant kinetic energy. When colliding with the source material, the ion beam will "sputter" the atoms of the target material.
These sputtered target ions (atoms converted into ions due to the influence of the ionization zone) also have kinetic energy and produce a dense film when in contact with the optical surface. IBS is a precise and highly reproducible technology.

3. Plasma sputtering
Plasma sputtering is a general term for a series of technologies, such as advanced plasma sputtering and magnetron sputtering. Regardless of the technology, it includes the generation of plasma.
The ions in the plasma are accelerated into the source material, colliding with loose energy source ions, and then sputtering onto the target optical element. Although different types of plasma sputtering have their unique properties and advantages and disadvantages, we can bring these technologies together because they share a common working principle, and the differences between them are much smaller compared to the differences between this coating technology and other coating technologies discussed in this article.

4. Atomic layer deposition
Unlike evaporative deposition, the source material used for atomic layer deposition (ALD) does not need to evaporate from the solid, but exists directly in the form of a gas. Although the technology uses gas, a high temperature is still required in the vacuum chamber.
In the ALD process, the gas-phase precursor is transmitted through non overlapping pulses, and the pulses are self limiting. This process has a unique chemical design, with only one layer adhered to each pulse, and there are no special requirements for the geometric shape of the optical surface. Therefore, this process allows us to highly control the coating thickness and design, but it will reduce the deposition rate.

5. Subwavelength structured surface
The surface structure smaller than the wavelength of light has become a research topic in the optical field, inspired by the texture patterns on the eyes of moths. Surface texturing is still a developing technology, which requires changing the structure of the substrate surface, unlike traditional thin film deposition of alternating high and low refractive index materials.
The features on the texture surface can be random or periodic, similar to the pattern of a moth's eyes. For the manufacturing of sub wavelength structured surfaces, if we want periodic patterns, we can use photolithography. If we want random patterns, we can use improved plasma etching.

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The subtle impact of optical design on manufacturing

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The subtle impact of optical design on manufacturing

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