Seeing a tiny green dot on a plane two miles away is not going to be easy.
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If you start with a 1mm beam size, color 532 nm (green), the spot size will be about 12 feet in diameter at 10,000 feet distance. It will be bigger if the air is turbulent and smaller if the laser aperture is bigger.
If you are scanning the sky, you'll see the laser beam going up. If you hit something shiny with the beam, you'll see a bright spark that's the reflection. You'll know you hit something shiny, and would not know if it was a mylar helium baloon or a 757, unless you also saw the plane's lights.
Didn't realize that. I thought the whole idea of the coherent light emitted from a laser was to keep the beam tight. Wouldn't the power of the laser be distributed in the larger area? So a 100mw laser would divide over 113 sq ft so it would produce 6uw sq/in. (math may be off a bit, but that's still very little power, certainly not enough to blind a pilot)