Optical coating-the definition of optical film
Optical film is ubiquitous in our lives, from precision and optical equipment, display equipment to optical film applications in daily life; for example, glasses, digital cameras, and various household appliances that we usually wear. Or the anti-counterfeiting technology on banknotes can be called an extension of the application of optical film technology. If there is no optical thin film technology as the development basis, modern optoelectronics, communications or laser technology will not be able to make progress, which also shows the importance of optical thin film technology research and development. What we bring to you today is the application principle of optical coating.
Definition of optical film
The definition of optical film refers to the thin and uniform dielectric film layer attached to the surface of the optical device during the propagation path of light. The characteristics of reflection, transmission (refraction) and polarization of the dielectric film layer, so as to achieve the special transmission of light in a certain or multiple bands, or the total reflection of light or polarization separation, etc. Form of light. Optical film refers to the preparation or coating of one or more dielectric films or metal films or a combination of these two types of films on optical elements or independent substrates to change the transmission characteristics of light waves, including light transmission, Reflection, absorption, scattering, polarization and phase change. Therefore, through proper design, the transmittance and reflectance of the surface of different waveband components can be adjusted, and the light of different polarization planes can also have different characteristics.
Generally speaking, the production methods of optical films are mainly divided into dry and wet production processes. The so-called dry method means that no liquid appears in the entire processing process. For example, vacuum evaporation is in a vacuum environment, where the solid raw material is heated with electric energy, after being sublimated into a gas, it is attached to the surface of a solid substrate to complete the coating. Processing. The golden, silver or metallic packaging film used for decoration in daily life is the product made by dry coating. However, in consideration of actual mass production, the application range of dry coating is smaller than that of wet coating. The general method of wet coating is to mix ingredients with various functions into liquid coatings, apply them on the substrate in different processing methods, and then dry and solidify the liquid coatings to make products.
The slightest difference is a thousand miles away. Optical film preparation is one of the fields of precision manufacturing, and its precision often reaches the nanometer or even micro-nano level. Therefore, the complexity of its preparation is self-evident. Sometimes small mistakes can lead to failures. It is very difficult. The preparation of optical thin films is a complicated process. It is obtained by evaporating or sputtering a large solid material, transporting it in the gas phase, and finally condensing on the substrate. The preparation process includes environmental vacuum conditions (vacuum degree), The influence of multi-faceted process factors such as evaporation rate and substrate temperature has greatly deviated the microstructure and chemical composition of the film from the ideal state, and ultimately led to changes in the mechanical properties, laser damage resistance threshold, and optical properties of the film.
Among the many process influencing factors, the thickness uniformity of the film is often the most influential and easy to observe, which will seriously affect the physical properties of the film. According to the preparation experience, the uneven thickness of the film will lead to the film thickness uniformity. The spectral performance has a large deviation. For example, the transmittance of the film will be low during the preparation of the antireflection coating. Secondly, it will also affect the laser damage threshold of the film, the film stress, etc., as the head of the article said: The slightest difference is a thousand miles away. Therefore, thin film preparation equipment is often equipped with a highly accurate film thickness monitoring system.