There are many reasons for the optical coating and related knowledge of PVD coating machine to affect the transmittance of a plane lens. The roughness of the mirror surface will cause the incident light to diffuse and reduce the transmittance of the lens. In addition, the optical absorption and rotation of the material will also cause some of the incident light sources to dissipate particularly severely. For example, a material that absorbs red light looks green. However, these poor processing factors can be removed as much as possible. It is a pity that there are inherent flaws in nature. When the incident light passes through different media, reflection and refraction problems must occur. If we incident the material perpendicularly, we can define the reflectance and transmittance
        Many people will ask curiously: How much light transmittance should a piece of perfect uncoated glass have? Since the light transmittance of uncoated glass is not good, after adding several layers of coating, the light transmittance should be worse? The refractive index of the coating is actually the same between these two issues. As long as the first problem can be understood, the rest will naturally be solved.
        According to the basic theory of electromagnetics, the transmission and reflection of different media are mentioned. If it is incident from the medium n1 perpendicular to n2 reflectivity = [(n2-n1) / (n1+n2) ]2 transmittance = 4n1n2 / (n1+n2)2 Example If the refractive index of air is 1.0, the refractive index of the coating nc (for example: 1.5), the refractive index of the glass n (for example: 1.8) (1) The penetration rate of glass entering directly from air = 4×1.0×1.8 / (1+1.8 )2 = 91.84% (2) Entering from air The penetration rate of the glass after coating = [4×1.0×1.5 / (1+1.5 )2] × [4×1.5×1.8 / (1.5+1.8 )2] = 95.2% It can be seen that coated glass will increase light transmission degree. In addition, with this formula, we can calculate that the light penetrates both sides of the lens and find that even a perfect lens (refractive index 1.8) has a light transmittance of about 85%. If a layer of coating (refractive index 1.5) is added, the light transmittance can reach 91%. Visible the importance of optical coating.
         Coating thickness of PVD coating machine The last thing we want to discuss is the difference in coating thickness of vacuum coating equipment, what effect will it have? We already know that the light transmittance is related to the refractive index of the PVD coating machine, but it has nothing to do with its thickness. However, if we can work hard on the thickness of the coating of the vacuum coater, we will find that the reflected light A and the reflected light B are different by an optical path difference of nc×2D. If nc×2D=(N+ 1/2)λ where N= 0,1,2,3,4,5..... λ is the wavelength of light in the air, it will cause the reflected light of this specific wavelength to have phase Therefore, the color of the reflected light will change.