The beams are easily seen, but not as bright as they appear in photos. The scatter is from the few particulates and the air itself. The scattering is primarily in the forward and backwards direction, so it looks much brighter if you are viewing along the beam, as opposed to viewing the beam from the side.

As the beam goes up through the atmosphere the air becomes thinner, and at 25km or so is not visible... (as seen by the telescope)

At around 85km there is a layer of sodium atoms about 10km thick... these sodium atoms are deposited constantly by meteors burning up in the upper atmosphere. And they are removed when they combine with the rarified water molecules up there. At any time there are a few kilograms of sodium atoms in this layer around the earth.

The laser is precisely tuned to the sodium D2 Transition at 589nm (yellowish orange). The sodium atoms absorb these photons and then re-emit them. This creates a column of glowing atoms where the beam intersects the sodium layer. When viewed end on by the telescope this column appears as a 10th magnitude yellow star. By looking at how the light from this 'star' is distorted by the atmosphere, you can use deformable mirrors to reverse the effect of turbulence... this is called Adaptive optics. You can use this to achieve near the diffraction limit...

You need a bright star to do Adaptive optics, but there is usually not one near what you want to view. The laser lets you create one exactly where you need it.

I will try to post more later...