Gray: those lasers actually *are* quite powerful, to reach up to that altitude. Even if it doesn’t slice aircraft in two, effects of a beam hit could not be pleasant (e.g. pilots could be blinded)
I do not know about every observatory, but I have been at an atmosphere research institute that operates a powerful LiDAR, which is basically a laser very similar to what we talking about here, but pulsing. That observatory used radar to automatically switch off the beam in case an aircraft came near.
In addition, I guess they issue NOTAM’s and perhaps temporarily close airspace when they operate the laser.