How bright a laser would I need to see the light bounce back from those reflectors we left on the Moon?

Answer 1

Bright isn't a very good choice of word. The laser you use doesn't even have to use visible light.

The true answer to your questions depends upon what kind of detector you are going to use. The reflectors on the moon are formed like the corner of a box. This has the geometrical property that the reflected beam will come back to within a couple of inches of where it started. You could then use a very sensitive photomultiplier and a filter that only allows the frequency of light in your laser to pass through. This would make it possible to detect very, very faint light.

So, no, you don't need a heavy duty industrial cutting laser to do this.

I know that they are doing this kind of work at the McDonald observatory in the Davis Mountains near Ft. Davis, Tx. I'll go look at their web site and see if they say anything about it.

Funny. They talk all about the telescopes and detectors, but they don't say anything about the lasers they use.

K, found it. The important thing to notice is that they are using a 1500 mJ laser, or, a 1.5 Joule laser.

LASER / SPECIFICATIONS / DATE / FUTURE /APPROX./
/ / / CHANGES /DATE /


Type of Laser Medium /YG402DP/ 4-11-94
Energy / Pulse (mJ) / 1500 mJ/ 4-11-94 / / /
Pulsewidth (ps) / 200 ps/ 4-11-94 / / /
Beam Size / 7 mm/ 4-11-94 / / /
Beam Divergence(Half Angle) .075 microrad/ 4-11-94 / / /

Answer 2

Extremely bright. And sent through a telescope. The problem is that by the time it hits the moon, the laser beam is 4 miles wide, while the reflector is only a foot and a half wide. By the time the laser comes back, that returning beam again is 4 miles wide.
So, only 1 /100 million of the light sent returns. If your telescope on earth is big enough, you may hope to get 1/10 million of what reflected off the moon. So in the end, the returning beam is a thousand trillionth (10^-15) of what was sent.

To put that in perspective, a mundane laser pointer is 5 milliwatt. To get a continuous beam that bright from the moon would require your laser to emit 5E12 watt, that is 5000 gigawatt. That is about 10 times the total electrical power produced in all of the United States, combined.

Answer 3

a laser as bright as rosie o donnell is fat.

Answer 4

i really dont know cool question, do u live next to an observatory? ank them they might know. i want to know to email me when u get the answer.