From: Richard Aiken

> I can see that. For one thing, I imagine any conceivable focusing mirror for any significant fraction
> of that amount of light would melt well below that level.

Nah, just make it bigger. The other problem is that the actual limit is 'as bright as the sun, if it covered the same fraction of the sky as the mirror does', so to even reach that limit you need an array of mirrors that covers the entire sky (or at least, the entire sky as visible from the point that is being targeted). For lesser coverage, multiply total energy by (sky coverage in steradians)/2pi.