There are many reasons for the optical coating and related knowledge of pvd coating machine to affect the transmittance of a flat lens. The roughness of the mirror surface will cause the diffusion of incident light and reduce the light transmittance of the lens. In addition, the optical absorption and rotation of the material will also cause some of the frequencies of some incident light sources to be dissipated particularly seriously. For example, a material that absorbs red light will appear green. However, these poor processing factors can be removed as much as possible. It is a pity that there are inherent defects in nature. When incident light passes through different media, problems of reflection and refraction must occur. If we enter the material normally, we can define reflectivity and transmittance.

       Many people will be curious to ask: how much light transmittance should a piece of perfect and uncoated glass have? Since the light transmittance of uncoated glass is not good, after adding several layers of coating, the light transmittance should be even worse? The refractive index of the coating is actually the same as these two issues. As long as you can understand the first problem, the rest will naturally be solved.
       According to the basic theory of electromagnetism, the transmission and reflection of different media are mentioned. If the medium n1 is vertically incident to n2, the reflectivity = [ (n2 -n1) / (n1+n2)]2 transmittance = 4n1n2 / (n1+n2)2 For 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 glass n (for example: 1.8) (1) from the air directly into the glass Penetration = 4 × 1.0 × 1.8 / ( 1+1.8 )2 = 91.84% (2) from the 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 the coated glass will increase the light transmission Spend. In addition, from this formula, we can calculate that light penetrates both sides of the lens and find that even a perfect lens (refractive index 1.8) has a transmittance of about 85%. If a layer of coating (refractive index 1.5) is added, the transmittance can reach 91%. The importance of visible optical coatings.
       The thickness of the pvd coating machine coating Finally, what we want to discuss is the difference in the coating thickness of the pvd coating equipment, what will be the impact? We already know that transmittance is related to the refractive index of the vacuum coater coating, but not its thickness. However, if we can work on the thickness of the pvd coating machine coating, we will find that the reflected light A and the reflected light B differ 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 the specific wavelength to have a similar cancellation effect, so the color of the reflected light changes.