the ATL beam will breakup long before
Everyone is hoping for success for the the highest of hi tech, physics notwithstanding. First of all, why have the ABL and ATL become about fielding untested coil lasers. We have already done chemical laser testing (HF/DF) with huge success on the ground for over 20 years. Testing planes on the ground with a laser inside reaches the ridiculous.
In the vacuum the beam diameter at the target stated in this article would be a challenge. But the plane must lase through atmosphere (and jitter not felt on the ground platform). It is easy to calculate that the ATL beam will breakup long before reaching the target at a 20 Km range, even if the target is at 100 m off of the ground. The energy from the beam will be spread at least over an area 10 times in diameter of the vacuum spot size. So much for the new marketing of the ABL and ABL lite (ATL), "invisible" indeed! I wouldn't want to be anywhere near the target of this "precision" weapon, especially not in the aircraft.