In optical elements, light energy is lost due to the reflection of the element surface. In order to reduce the reflection loss on the surface of optical elements, transparent dielectric films are usually coated on the surface of optical elements. This kind of film is called antireflection film. From the perspective of energy conservation, the transmittance of optical elements is enhanced. According to Fresnel formula and refraction law, the transmission principle of antireflective film is quantitatively explained; The principle of improving the transmission rate of antireflection film is explained by using the electromagnetic transmission theory of electrodynamics.
Antireflective film on glass and plastic substrates.
In many optical systems, a very important part is to coat the lens with a coating that can reduce reflection. In many applications, antireflection film is indispensable, otherwise it can not meet the application requirements.
In a 35 mm autozoom camera composed of 18 lenses, it is assumed that the interface reflectivity of each glass and air is 4%, the transmittance of the non-enhanced lens is 27%, the transmittance of one layer of film is 66% (residual reflectivity is 1.3%), and the transmittance of multilayer film (residual reflectivity is 0.5%) is 85%.
Do you need to pay attention to the processing of lens?
When light enters different transmission materials (such as from air to glass), the reflectivity is about 5%. There are many lenses and refractors in the optical line of sight, which will cause the loss of incident light up to 30% to 40%. Modern optical lenses are usually coated with one or more layers of magnesium fluoride antireflection film, which can reduce reflection to 1.5%, and multilayer antireflection film can reduce reflection to 0.25%. Therefore, if the coating is proper, the light transmittance of the whole line of sight can reach 95%. The lens coated with multilayer antireflective film is light green or dark purple, while the lens coated with single-layer antireflective film is usually blue purple or red.
The essence of improving transmission intensity is that the energy distribution of light wave as electromagnetic wave on different media interfaces changes due to different boundary conditions. Generally, optical lenses are used in the air. For optical glass with refractive index of about 1.5, in order to achieve 100% antireflection effect, the thickness of the antireflection film can be made n 1=1.23 or close to 1.23, and the thickness of the antireflection film can be made equal to one quarter of the (2k+1) wavelength. The monolayer only increases the transmission of electromagnetic wave at a certain wavelength. In order to realize the transmission of electromagnetic wave in a larger range and more wavelength range, people use multilayer coating to realize the transmission of electromagnetic wave.
People have rich experience in using antireflective coatings and have found many materials that can be used as antireflective coatings. At the same time, they have mastered many advanced painting technologies. Therefore, the application of antireflective coatings involves many industries such as medicine, military, aerospace exploration, and has made great contributions to the progress of human science and technology.