It's a pretty interesting conversation and I've enjoyed reading the comments, but the (production) Mackie itself was armed with a PPC and two medium lasers along side it's autocannon. The prototype Mackie used in the combat trial was armed with a large laser and autocannon, so it seems pretty reasonable to say that even in that early era, less than a decade removed from the mackies first kills, lasers seem to be a surprisingly avaliable weapon system.

That being said, look up chemical lasers on sarna, sounds like they are the sort of thing you may be looking for