The FROM WHERE question is a good one.
This is all really wild speculation based on questionable photos that none of us have seen, but . . .I fear that the technology is here or will be soon. How to deploy it successfully for this kind of attack would call for some sneaky thinking but even that is not hard to come by.
I don't think you proponents of this understand EXACTLY how much power you're talking about here.
If the Chinese could shoot down the space shuttle over California, we'd be ABSOLUTELY DEFENSELESS against them. No plane could launch, no bomber, no missile, nothing.
Even programs like HAARP doubtfully have the power to direct a coherent beam of light on a TINY target 4,000 miles away.That's what you're talking about... firing a coherent PINPOINT beam weapon over 1/3 + of the Earths diameter at a moving target.
I don't doubt computing power - I doubt the current level of physics. If we could do that with optics, we'd be launching orbital vehicles with them.