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The magic of reflection and transmission: How do anti-reflective coatings reduce light loss?
Optical coatings are one or more thin layers of material that are deposited on optical components, such as lenses, prisms, or mirrors, to change the way light is reflected and transmitted. These coatings have become key technologies in the field of optics. One type of optical coating is anti-reflective coatings, which are used to reduce unwanted reflections from surfaces and are often found on eyeglasses and camera lenses. The other type is high-reflective coating, which can be used to make mirrors with a reflectivity of more than 99.99%.
Among these optical coatings, anti-reflective coating technology is the most well-known. It effectively reduces light loss and greatly improves the performance of optical elements.
Types of optical coatings
The simplest optical coatings are thin layers of metal, such as aluminum, which are deposited on a glass substrate to create a mirror surface, a process known as silver mirroring. The metal used for the mirror will determine its reflective characteristics. Aluminum is the cheapest and most common coating, with a reflectivity of about 88%-92% in the visible range. Silver is more expensive, its reflectivity can reach 95%-99%, and it performs well even in far-infrared rays. But in the blue and ultraviolet spectral regions, the reflectivity drops to less than 90%. Gold is the most expensive, but its reflectivity in the infrared range is excellent, reaching 98%-99%, but its reflectivity is limited at wavelengths below 550 nanometers.
Anti-reflective coating technology
Anti-reflective coatings are primarily used to reduce surface reflections. When a beam of light passes from one medium into another, such as when light passes from air into glass, some of the light is reflected back from the interface. To reduce reflections, the simplest approach is to use a layer of material whose refractive index lies between the two media. When the thickness is precisely controlled to be a quarter of the wavelength of light, the front and rear reflections cancel each other out to achieve minimum reflectivity.
Multi-layer anti-reflective coatings can achieve a maximum reflectivity of less than 0.5% in the visible light range by designing the thickness and composition of the layers.
Application of high reflective coating
High-reflective coatings perform the exact opposite function of anti-reflective coatings. The design of these coatings is usually based on a system of periodic layers of materials with different refractive indexes, with thicknesses adjusted to achieve maximum reflection and minimum transmission. For example, these highly reflective coatings can be used in specific applications of lasers to tune the reflectivity to the specific value required.
Highly reflective coatings can achieve 99.999% reflectivity, making them ideal for applications within specific wavelength ranges.
Transparent conductive coating and its application
Transparent conductive coatings excel in applications where the coating needs to conduct electricity or dissipate static electricity. For example, transparent conductive oxides such as ITO are widely used in flat panel display technology. This type of coating is not only conductive but also maintains high transparency as light passes through it.
Future optical coating: Fano resonance coating
Fano-resonant optical coatings (FROCs) are a new type of optical coatings that exhibit photonic Fano resonance properties. This type of coating can achieve detailed and efficient filtration effects in different applications, and its adaptability makes these coatings have broad potential in the fields of decoration, anti-counterfeiting and even solar power generation.
The structural dyeing properties of FROCs allow them to produce high-brightness and high-purity colors across a wide range of colors and can be adjusted according to the angle of incident light.
Anti-reflective coatings not only improve the performance of optical equipment, but also promote the development of many new technologies. The application of these coatings will continue to play an important role in the future evolution of technology, changing the way we understand and use light. Do you look forward to the new possibilities that further breakthroughs in optical technology will bring to our world in the future?
