You only get a couple photons back from a laser burst according to UCSD.
This is a good example of the worthlessness of uninformed incredulity.That's right, you only get a couple of photons. But they're enough.
Yes, even when the laser is off the moon sends many photons toward the earth. But not all photons are the same, and that's the crucial difference. For the telescope to count a particular photon it must first pass this gauntlet:
1. The telescope sees only photons from a tiny part of the lunar surface centered on the reflector in use. All other lunar photons don't even make it through the telescope.
2. The detector only sees photons with the wavelength of the laser. Reflected sunlight is spread over many wavelengths, so most are filtered and ignored.
3. Most important of all, the ranging system already knows the approximate distance to the moon so it only responds to photons arriving within literally nanoseconds of the expected time.
These criteria are so selective that when you apply them to the huge numbers of reflected solar photons, essentially
none make it through. And that's what makes it possible to detect those few laser photons that do make it back to the telescope.
The Mythbusters episode, if you watched it, showed a scatter plot of received photons vs time at the Apache Point site. When the laser was off or not pointed at a reflector, you only saw a few points scattered randomly over the graph. When a return was acquired, a very obvious black bar of dots formed right across the middle. There is simply no way around it: the system works, and only because of the artificial reflectors placed there by Apollo and Luna.
