Reaching for the stars, finally - will the young ones among us get pics of Alpha C.?

[Anomalocaris]

Then let's talk about how good a superlight mirror has to be to reflect 2 Gigawatts and not be instantly vaporized... We are talking about required reflection losses of the order of a few parts in a billion, or something like 99.999999% reflectivity. One microscopic defect and poof it goes.

The laser would not need to be collimating to deliver a large number of watts per square meter if the mirror is very large, say 1000 m across.  In the case the mirror will receive only 3KW/sq meter.  This might prevent imperfection from bing immolated.

The trick is to make a mirror that big that has a reasonable mass, otherwise the necessary power per sq meter goes up, enough structural strength to survive earth gravity in folded state, ability to unfold correctly in space without too much help, and tough enough not to rip while delivering the thrust to its payload.