Not to say this is in any way practical, but lasers used for nuclear fusion research are up in the petawatt range. They've just got extremely short pulses. But

Not to say this is in any way practical, but lasers used for nuclear fusion research are up in the petawatt range. They've just got extremely short pulses. But if all you need to do is detect that pulse coming back, like a radar return, it starts to sound within the range of conceivable engineering, not a total physical impossibility.