I had laser eye surgery a long time ago and they have an interesting approach to destroying minute amounts of material behind a lens (aka my eye). They use two half strength beams that when focused independently intersect at the spot (delivering 100% power) where they want to burn away lens material. This was done repeatedly to remove a thin layer over a wider surface area with a high degree of 3 dimensional precision and minimal collateral damage.
If you multiplied this several times and had 10 or 100 or more lower strength lasers targeting specific high value targets, each laser would interact minimally with the barrier/glass dome reducing the effects of dirt/defects/heating. If the dome was underwater, sufficient ambient cooling might occur. All you need is multiple attack vectors with direct line of sight to the target (easy when attacking from above in a world with gravity sufficient to hold down water).
Another way to look at this is how a natural concave lens works or even a magnifying glass. It bounces/refracts light off a dome shaped surface/lens to focus on one point in the middle. In effect it's an infinite number of "lasers" pointing low power light into one spot of high intensity power.
Don't quote me, but I believe this multi laser approach might also be in use for military grade anti missile defense "shields" since it naturally provides layers of redundancy and reduces the risk of friendly fire/innocent casualties. For example slicing the wings off a nearby plane in the line of fire as the laser is tracking the target. Note that in this situation, the laser is aided by the explosive nature of the missile and fragility of precision guidance systems. 898
It's doesn't have to produce devastating destructive power on it's own.
Edit: there could be quite a cinematic opportunity here. It would literally be raining down lasers. You'd have people see little red dots appear like rain drops unaware of what's happening. A side on shot would show a "downpour" of red lines, and everything bathed in red. The lines would then swing around searching for a target. Masses of them would swarm on people or anything combustible. Then the explosions would start; barrels, gas mains, aircraft wings in mid flight... panic and people running seeking shelter. Large clouds of smoke and debris would refract the lasers into a blinding lightshow. When the dust clears, slowly the lasers switch off one by one like the lights on a stage. 580