The laser pointer is widely used in daily work and life. It is used as an indicator when explaining PPT in class, or as a marker for accurately indicating buildings from a long distance, or as a cat-playing artifact. The high-power laser pointer can ignite combustibles and cause fires. In addition, the laser pointer should not be directed at people's eyes, otherwise it will cause irreparable damage.
The laser pointer can easily illuminate walls and ceilings, leaving bright "small spots". So, how far can it shine? Can it shine on the moon? When playing with the laser pointer, people will find a problem: the farther the object is irradiated, the larger the spot area and the darker the color. This is because although the laser is highly collimated light, it will gradually diverge as the propagation distance increases and the air is scattered, and the brightness will gradually decrease.
Let's take the commonly used pen-shaped laser pointer as an example. Its power is about 5 milliwatts (0.005 watts). At a distance of 100 meters from it, the laser light source looks like a 100-watt bulb from 0.91 meters away, which is very dazzling. Pull the distance farther, if you observe the light it emits at an altitude of about 12,000 meters in a clear sky, the spot of the laser pointer will be as bright as the moon.
Observe further away? If there is a chance to board the International Space Station, the brightness of the laser pointer launched from the Earth to the space station will drop to the level of the brightest star in the night sky. Therefore, although the laser pointer can reach infinity in theory, the actual propagation distance visible to the naked eye is probably only a few hundred kilometers at most. So, can the laser pointer shine on the moon? As mentioned above, in theory, the light emitted by the laser pointer can reach infinity.
The distance between the earth and the moon is about 380,000 kilometers. Assuming that there is no cloud, the laser will properly illuminate the moon even if there is the influence of the earth’s atmosphere, but the scattered area of this light spot will be a bit large, almost It is the size of a small and medium-sized town, and the dim light spot cannot be seen clearly with the naked eye. Therefore, although the laser pointer can shine on the moon, it is impossible to use the laser pointer as the light source to "illuminate" the moon.
So if the most sophisticated laser emitting device on the earth or the military laser weapon can illuminate the moon, can it form a new light source similar to the sun? For safety reasons, the power of civilian lasers is often very low (generally no more than 1 watt), while the power of military laser weapons is much higher. Military laser weapons can really have the power, but based on their military use, most of them are installed on fighters or single devices. The total power of single or multiple laser weapons is far from the effect of illuminating the moon. At present, the most advanced calculation of the power of a single military green laser pointer requires 5 billion devices to beam at the same time to shoot at the moon. This consumption is something that no country on earth can afford.
So are there any cutting-edge state-level experimental lasers? Really! Take the Fast Ignition Test Platform (LFEX) in Osaka, Japan as an example. The power of the UV laser it emits can reach one trillion watts, which is about a thousand times the global power generation capacity. This device is usually used for experiments in fields such as nuclear fusion. If we have the same power of visible laser, we only need one, and we can shine the moon as bright as usual. It is a pity that the LFEX laser can only emit 1 picosecond (one trillionth of a second) at a time. Even if we can see the ultraviolet light, it is too late to capture the moment the moon is illuminated. How sad it was, finally concentrated the artillery fire, but the effect was over without being caught by the eyes.
With a bigger brain hole, if we once again, regardless of the cost, let each of the 7.6 billion people in the world own a super laser similar to the Japanese LFEX and shine on the moon at the same time, what will happen? This beam of light heats the atmosphere into plasma before leaving the earth, and then the surface begins to burn. After irradiating the moon, the moon will be thousands of times brighter than usual, and the rocks on the moon's surface will be heated to incandescent within 2 minutes.
This is cool, isn't it? You can melt the moon. but! This is still whimsical during the day, because if our technology can really evolve to a super laser, we should not be satisfied with the moon as a rake..