Why is a laser a line? Do the laser lines we see exist?

Strictly speaking, the laser beam is not considered a line, and the laser itself is actually divergent, but because the speed is extremely fast, the particles that are placed in various directions do not have time to diverge, so it will be regarded as a line.

The electromagnetic field of the laser is confined to a straight line" is not exact, but it should be the Gaussian speed of light, which diverges less than the ordinary speed of light. It is the theoretical calculation result of the coherent light + optical cavity model, and it is in line with the experiment. It is difficult to explain without a simple mathematical explanation, but I can only try to explain that coherent light diverges less than natural light, and that is because due to its coherence, the electromagnetic field that travels to the part of space far from the center of the speed of light cancels each other out and is concentrated, while natural light is divergent because it cannot cancel out due to incoherence.

Lasers are completely different from ordinary light, and most of the light sources we see in daily life are unrelated light sources, such as the light of a flashlight, the light of the sun, and the light emitted by a light bulb. The so-called incoherence refers to the fact that the light emitted from these light sources has two common characteristics, both of which are composed of different colors of light, which look like white light, and these different colors of light, even the light of the same color, have different polarization directions.

Specifically, first, the light they emit is distributed across frequencies, in other words, they are made up of a variety of different colors, and these different colors of light are superimposed on each other and emitted into our eyes, and all we see is white light. Second, these different colors of light, even light of the same color, are polarized in different directions. Polarization refers to the direction of vibration of light, for example, the light emitted from the smartphone screen is polarized, when we look at the phone screen with polarized sunglasses, we can only see the content on the screen from one direction.

When the screen is turned to a certain angle, the content on the screen will disappear completely, and the polarization direction of the mobile phone screen light and the polarization direction allowed by the sunglasses are completely perpendicular, so we can't see the content on the screen.

This is a normal laser emitter.

Its three rays of light converge together, forming a ray that instantly ignites a match.

The laser irradiates the bottom of a regular toilet paper.

Hold on for less than 10 seconds for the toilet paper to be pierced.

The laser shines on the top of the toilet paper and a match is placed on its back.

The toilet paper is laser pierced, and the hole instantly ignites the match in the rear.

Turn on the camera function of your Samsung phone and move the camera position to the laser illumination position.

You can see through the lens that there is a blackened appearance.

The phone went back to the main page, and the phone was not penetrated, it seems that the rear camera was damaged.

By placing the phone screen diagonally into the rays, you can see the laser light being refracted.

Although the laser light was refracted, the screen glass was severely damaged.