I used a neon laser to make a really straight line on an airfield strip. At 3 kilometers the beam diameter was about
1.5 meter. We used two vertical poles as a diaphragm at about 100 meters. That (almost) did not work ,you got a host of vertical stripes,with one slightly brighter in the middle,so in the end you lose the battle against the square law dimming and spreading.We also discovered that the runway was going up and down more than 2 meters. -( -(