I know this is an old old post and all, but thought I might chime in for future reference. More than likely there isn't a simple attachment for your router, I've personally never heard of any and lasers are my forte` (I'm a laser specialist for the DoD...sometimes). What you essentially would need is a "laser engraver". There are many vendors/brands out there but arguably Epilog Laser is the best. Attaching a high powered laser simply would be 1) Dangerous if not enclosed 2) Be only used to cut/burn, not so much engrave without proper laser setup.
Most engravers/cutters are Co2 lasers that use a "flying optics" setup in order to do the work. I can't say I've ever seen a diode setup used for actual engraving. I would suspect not only would it be extremely hard to find, as there isn't many 20w laser diodes out there, but extremely expensive as well. The laser you pull out of your "blu-ray" players and dvd players will "burn" surfaces but that's probably about it, as they're not too powerful (i.e. 1.6w isn't going to do a whole lot in the world of cutting acrylic/wood/plastics and even if it did it'll take you days to cut through). Metal is also out of the question unless you're using a certain setup like a Galvo laser or fiber laser, in either case very expensive machines.
One reason I came into this forum is that I have a strong interest in robotics and I'm getting a 75watt Epilog laser engraver soon and hope to do work for you among other enthusiasts. The working area will be 24x18x8 and I'll be able to remove the front in order to "poke" a larger piece inside for engraving. I'll be posting a "new member" post here soon giving more details and if you ever want to know more feel free to contact me, I'd love to help
Hope this clears some things up for you guys.