Using those numbers, the 500kw laser needs an additional 400kw worth of thermal management (some variant of a refrigeration system) to handle the losses of the laser and supporting power electronics... So double your generator power offtake (unless you opt for a mechanically driven refrigeration system... )...., and…

Beyond the laser we need better thermal management and battery technology before it will fly. (On anything beyond a C130) Even the best lasers are only 30% efficient, so at a megawatt that is a ton of heat. And the turbine engine isn’t going to be able to handle sudden pulse loading of the laser without some energy…