Compare how much a coherent laser visible green light beam spreads out with a incoherent green light beam.

It totally depends on the type of incoherence. If the source is spatially incoherent, it will spread by an angular amount corresponding to the angular size of the source as seen from the final beam- forming element, plus the amount that a beam formed from a spatially coherent source would experience. Temporal coherence doesn't really matter in your scenario. The presence of a clean thick pane of glass, at normal incidence, will not significantly affect either the beam size or its divergence.

Assume your incoherent light comes from a source smaller than the window and spreads out to cover the window. Then its angular divergence, defined as the angle between the light on the left edge and the light at the right edge, or the width of the window over the distance to the plane.

$$ Delta phi = w_{rm{window}}/d_{rm{plane}}$$

Any beam in these conditions will keep its overall beam divergence. A good laser might be smaller than the window at that distance. If so, the divergence in the window is given by that beam divergence. If larger, see formula above.

But I agree with the commentators: in any case, the effect of divergence as the beam goes through the glass is negligible.

@anna v, a theoretical physicist from Greece, wrote on Physics Stack Exchanges 3 years ago, "Coherence matters because it retains the angles , there is spacial coherence. With incoherent light there is large divergence.One could not shine incoherent light on the moon, for example. The incoherent spot on the unit sphere will diverge and enlarge proportional to r^2 as the radius grows. A laser beam spot due to coherence enlarges slowly as can be found in various links". – anna v Jul 3 '12 at 18:47 in this URL, How can a laser pointer have range of several kilometers in atmosphere?

The answer to my question is, The incoherent spot on the unit sphere will diverge and enlarge proportional to r^2 as the radius grows. Therefore: 1/2 mile = 804.5 meters 2 inches thickness = 5 centimeters So, (804.55 meters) * (804.55 meters) - (804.5 meters) * (804.5 meters) = 80 square meters difference which equates to the radius of the incoherent spot on the unit sphere growing by 5 meters over the final 2 inches of the aircraft cockpit window. I must admit that this result may needs to be corrected because it is relative to the unit sphere. Please correct me if you have the time.