Beam divergence
Twoonefour;
If you take the average beam divergence of a laser powerful enough to cause serious concern to an airliner at 23000ft, and shining directly into the cockpit which would give a slant range. You could easily consider a beam divergence of 0.3m per km (focussing the beam dependant)!!
You would have a beam divergence roughly 6.8ft in diameter or enough to fill the cockpit in visible laser light.