Laser pen is widely used in daily work and life, or as a class PPT indicator, or as a distance to accurately indicate the building marker, or as a cat playing master teasing the cat magic device. And powerful green laser pointer can ignite combustible materials, which can cause fires. In addition, the laser pointer should not be directly aimed at people's eyes, otherwise it will cause irreparable damage. Take the common pen-shaped laser pointer, which has a power of about 5 milliwatts (0.005 watts). At a distance of 100 meters, the laser source looks like a 100-watt light bulb from a distance of 0.91 meters. Further out, if the light from the laser pointer was observed at an altitude of about 12,000 meters in clear sky, the point of light would be as bright as the moon.
Even more imaginably, what would happen if once again, regardless of cost, each of the world's 7.6 billion people had a super laser similar to Japan's LFEX pointed at the moon? Before leaving the earth, the light would heat the atmosphere into plasma, which would then burn the surface. When it hits the moon, it will be thousands of times brighter than usual, and the rocks on the moon's surface will heat to incandescence in two minutes.
We must have had such experience when using the laser pointer: the farther the object, the larger the area of the spot, the dimmer the color will be. It is not difficult to find that although laser is a highly collimated light, it will still gradually diverge with the increase of propagation distance and scattering of air, and its brightness will gradually weaken. So we need a 20 milliwatt flashing green laser designator pointed at us from the moon in order to see it easily. A lot of green laser Pointers are underrated and emit more power than that.
You need to define what "clearly seen from Earth" means. Especially with a laser pointer or telescope observation, in the latter case, how much magnification is the telescope. I can tell you that it is impossible not to see any small objects on the moon with the naked eye. The only exception might be a nuclear explosion on a very dark night, and even then it would only be visible for a split second. Even with the use of a laser pointer, all the laser light will be dispersed and will be distributed within 384,000 kilometers of earth. Even if we could get highly collimated light sources, it would be impossible to aim at a single eye on Earth from the moon.
