in order to filter out glare reflected from surfaces such as water, some sunglasses have polarizing films. In my opinion, polarized glasses have a more interesting use-they can help people discover hidden colors in the transparent world.

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as long as you have polarizing glasses (or polarizing film), it is not difficult to see this hidden color. All you have to do is turn on your computer (actually a cell phone is fine), set the screen background to pure white, wear polarized glasses, and bring transparent plastic forks, rulers and other items to the computer screen for observation.

(a simple way to check whether your sunglasses are polarizing lenses: hold them in front of the computer screen and turn them in the direction of rotation. If you can clearly see that the light and shade of the picture in the lens is changing, then it is the polarized glasses. )

spoon:

ruler:

goggles:

the colorful stripes suddenly appear on these originally colorless and transparent objects. It is a very pleasant process to appreciate it, but it is much more painful to explain it. Let's take a brief look at the principle of this color stripe: ∠)

this phenomenon is called photoelasticity, or stress birefringence. To put it simply, these color stripes reflect the stress distribution inside the plastic products. In the process of processing, there is an uneven stress inside the plastic products, which leads to changes in the structure and optical properties of local materials. It is this difference that enables us to see color stripes from transparent plastic forks and plastic rulers through the polarizer.

of course, the above explanation is extremely crude. It will be more troublesome to explain in detail. I will try to talk about it below. This part can be read as appropriate: ∠)

. In fact, it is the birefringence of these plastic products under the action of stress. Birefringence is a special refraction phenomenon: when a beam of light is incident, there are two pieces of refracted light. The two refracted light produced in this way not only have phase difference, but also are polarized light, and the polarization directions are perpendicular to each other.

originally, this special refraction occurs on some crystals, but amorphous materials such as plastic and glass will also show the characteristics of birefringence (that is, stress birefringence) when they are pulled by a certain stress.

the color stripes we see through polarizing lenses are actually the result of the interference of two refracted light produced by birefringent materials. According to the law of refraction, when a beam of light is directed vertically towards a transparent material, the direction of the light does not deflect, but the propagation speed of light is affected by the refractive index of the material. In the case of birefringent materials, two beams of light with different phases are produced.

two beams of light with different phases should interfere, just like reflected light with different phases in thin film interference. the result of their interference will be that some wavelengths of light are enhanced and others are weakened. so eventually the white light will become colored.

however, there is another condition for polarized light to interfere: they should vibrate in the same direction. The two lines of refracted light from birefringent materials do not satisfy this condition: their polarization directions are perpendicular to each other. Therefore, to see the color interference fringes also need the help of a second polarizing film, which can make the two groups of polarized light perpendicular to each other end up with only components in the same direction. Finally, the interference effect can be seen through the refracted light of the second polarizing film.

(that's about it. )

there are also related articles at the squirrel meeting, you can refer to: http://songshuhui.net/archives/16467

principle may indeed be out of line, but after all, the phenomenon is still very beautiful, and it is not difficult to observe, so I hope you can also enjoy ~