Unfortunately I can’t open the links on my phone so it’s hard to follow what you’re describing. I understand the rays aren’t perfectly parallel but they’re pretty close to parallel. Do you mind doing the math of where you are getting 3km from I’m not really following your logic. It doesn’t make sense to me that the light should suddenly spread out way more after bouncing off a mirror than if it has just continued traveling straight.
I get what your saying now but it would be possible if you made the mirrors with a focal point at 300km and it would be less effective at different lengths but it shouldnt change all that much since you would only need like a couple seconds with that kind of intensity.