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Some of the laser light emitted by the Laser pointer can be seen with the beam, and the beam will follow wherever it is irradiated, while some cannot be seen. Do you know why?

What is the Tyndall effect?

If the laser is not directed at you in a vacuum, you will not be able to see it. However, the air we breathe together is not a vacuum. Among them are dust, suspended particles and so on. The bright "passage" of the laser light is formed by the scattering of light by these particles. We call it the "Dyndall Effect". Light is when the electrons in the atom absorb energy, transition from a low energy level to a high energy level, and then fall back from a high energy level to a low energy level. The energy released during the fall is released in the form of photons. Light travels in a straight line. An example is usually mentioned. When the floor is sweeping in the classroom, there is sunlight through the bed glass, and we can see that the sunlight is straight. The sunlight shining on the dust is diffusely reflected, so we can see the propagation path of the sunlight from all directions. In the same way, although the laser is a parallel beam, it will be reflected in all directions by the air and dust during the process of spreading in the air, so it can be seen from all directions. If it is in a vacuum, it can only be seen by facing the laser against the direction of laser propagation.

Visible Green laser pointer beam in astronomical applications

The main purpose of using lasers in astronomical observatories is to combat atmospheric interference, especially the interference of tropospheric air close to the ground, in order to obtain clearer astronomical images. The earth is surrounded by a thick atmosphere, which not only reduces the brightness of the stars, but also interferes with the shape of the stars. This interference is very powerful, even visible to the naked eye, and it is precisely it that produces the "flash and flash". Astronomical phenomenon.

After years of exploration, astronomers have explored an adaptive optics system that can automatically counteract the interference caused by the atmosphere, but this system requires a sufficiently bright guide star as a basis for correction, but the sky usually lacks Such a star, so some people thought of using a laser to artificially create a bright star. For example, sodium laser guide star.