SZLASER

A very important coating is a reflective version that produces mirrors, coated on the front or back transparent optical material or on the front surface of metallic substrates. This kind of coating reflects a high amount of energy (light in the visible range), which is important for its intended use. As the AR coatings, reflective coatings are also designed for different regions of the spectrum. Aluminum is the most common metallic coating material. Table below shows different kinds of coating materials and the percentage of reflection in different wavelengths. The other type of optical coating used for reflection purposes is the dielectric coating, which uses thin layers of transparent dielectric materials with different refractive indices (e.g., magnesium fluoride or calcium fluoride) and various metal oxides that are deposited onto the optical substrate.

The principle of reducing reflection and increasing transmission of light works due to the "interference" phenomenon. In the visible spectrum range, each surface of an optical glass element reflects about 4% energy; thus, if 100% energy enters the first surface, about 92% comes out of the second surface. This is bad for optics. Table below shows two examples of what happens if more elements (and more surfaces) are in the optical assembly. The reflection of light from one surface is given by where N0 is the refractive index of the first medium, and N is the refractive index of the second medium. When the first medium is air (N0 = 1), the reflection from the uncoated surface can be expressed by For normal incidence light (perpendicular to the surface), the reflection can be calculated by where m0 is the number of surfaces, and n is the refractive index of the medium (material). But how do the interference phenomena work? The addition of a layer with a thickness one-quarter of t...

Optical-element surface coatings have an important task in the functionality of optical elements and optical assemblies. In most cases they enable the elements or assemblies to perform according to systems requirements. Coating requirements, specifying mostly optical and durability properties, are defined in the drawing of the element to be coated and in a special coating specification. Optical coatings can be classified as follows: According to its function Reflective coatings (metallic and dielectric), Antireflective (AR) coatings (single- or multi-layer, narrow- or broadband), Transparent conductive coatings, Beamsplitters, Filters (high-, low-, and band-pass), High-efficiency (HE) coatings, High durability (HD) coatings, and Diamond-like carbon (DLC) coatings; According to the spectral wavelength range Ultraviolet: ~0.2–0.4 mm, Visible: ~0.40–0.75 mm, Near infrared (NIR): ~0.75–3.00 mm, Mid infrared: ~3–5 mm, and Far infrared: ~5–20 mm. Reflective coatings can be classified in the ...