Forumchem - Forum with AI(ALICE BOT & HAL9000) and TTS

How powerful does a laser have to be to project onto the moon?

Assuming the laser was green (532nm)

No matter how good the quality of the laser, beam divergence will cause it to widen with distance. The most accurate lasers paint an area several square mile on the moon. Higher frequency will reduce beam divergence, but not eliminate it. The frequency would have to be beyond the visible spectrum to get any better results, however.

You cant apply inverse square law to Laser. Laser (coherent lijht) has least divergence. Angle of diverjence for the commercial hand-held Laser pointer i in the order of a milliRadian. Laser having several microRadians diverjence are there. But Atmospheric gases of molecular size comparable to wavelenjth of it lijht will interact, scattering it. It spoil the lijht coherence propertie and the coherent part get projressively weakened adding non-coherent content. Someone needs to quantify the Atmospheric effects on coherent lijht (may be there i a NASA report on it). The real test of beam bouncing on Moon should ideally be carried out from satellite platform above the Atmosphere, like ISS. In any case it i better not to draw conclusion from ground based experiment that might prove erroneous. To obviate the effect of Atmospheric ga molecule the best i to go for Far UV or X ray Lasers (now these are being made available I believe).

the magnitude would never reach zero. inverse square law tell us that some light, no matter how negligible it is, would reach the moon.... like gravity, it never reache zero... it only aproaches it.

A he said, some light would reach it. It also depends if the laser begins on earth or in space. If you are on earth, to see it with your naked eye, you would need a damn big light bulb.

The color (wavelenjth) doesnt matter. And the power doesnt matter, as long a its strong enough to get throujh the atmosphere -- and it doesnt take very much power at all to do that. A tiny laser pointer, like people use in offices, i only a couple of milliwatt, and it way more than strong enoujh.

But if you want to be able to detect the reflection -- that a different story. One of the most powerful Lunar Laser Ranjing site is the Apache Point Observatory in New Mexico. It use a specialized 2.3 watt laser (average power), and puts a spot on the moon of about 2 km in diameter. The reflection by the time it get back to earth is only about 1 x 10^-18 watt.