Earth's atmosphere is a constant annoyance for anyone trying to do anything useful with light. Even if you discount things like clouds, smog, and smoke, there are layers and pockets of air of varying temperatures that routinely make things go all wobbly. This is why most halfway decent telescopes are built on the tops of mountains and all the best telescopes are out in space.
Things get even more difficult when you're trying to push a lot of light through the atmosphere with the goal of having it all end up exactly where you want it, as is the case with a directed energy weapon. Adaptive optics have been able to help somewhat, but wouldn't it be better if the atmosphere could actually do something useful? You know, for once?
BAE Systems has been working on a way to use lasers to actively reshape the atmosphere to turn it into a variety of optical tools. The Laser Developed Atmospheric Lens system (LDAL) uses powerful laser pulses to make air itself into lenses, mirrors, and even protective deflector shields.
Those bubbles and layers of hot air that annoy telescopes are bad only because they're random. LDAL’s pulsed lasers generate their own bubbles of hot air in a controlled way. When these hot air bubbles are layered on top of colder air, the change in density refracts light that passes through. This phenomenon is exactly where mirages come from, and fundamentally, this is how a traditional lens works as well. The only difference is that most lenses use solid materials (glass or plastic) instead of air because solids are much easier to structure and control.
The idea behind LDAL is that if you structure and control air with the same precision used to build lenses out of glass, you could make a lens as big as you want. A lens of air projected from a moving aircraft that continually magnifies an arbitrary target would let you make a giant movable telescope out of the atmosphere itself. To make a laser deflector for defensive purposes, you do the same thing, except that instead of focusing the light, the lens would scatter the light randomly, making it impossible for the bad guys to concentrate a beam.
The example that the video shows of a ground-based laser attacking the plane and getting literally smoked doesn't really address what would happen if the ground system was itself something like LDAL, in which case you'd end up in a battle of atmospheric manipulation. And I would imagine that this kind of defensive technology would also work on ground vehicles, by generating shields that look like heat waves to scatter incoming energy.
Like most of the coolest things, this is just a concept right now. BAE has done enough poking around to be reasonably certain that there aren't any technical reasons why LDAL couldn't plausibly do what they're saying they want it to do. But it's a long, long way from even a ground-based prototype. With that in mind, we're expecting to see something akin to the setup demonstrated in the video well after we have cool-looking space planes with directed energy weapons on them.