Cool stuff!
I was briefly involved in a project attempting to use lasers to communicate between satellites in low-earth-orbit. This was about 12 or 14 years ago, and used 800mW IR laser. The big problem was getting the laser to live more than 100 hours or so, and getting the collimating optics lined up properly. Since the light only had to travel xx thousand miles, aiming wasn't considered to be a big problem.
In this case, shooting the laser all the way from earth to Mars, aiming will be pretty darned tough! Granted, you can make the beam diverge a bit more, in hopes of actually shining some light on the receiver, but that'll reduce the signal strength. Heck, on our satellite-to-satellite laser system, the receivers were getting so little light that it was claimed that the detector was basically counting photons (seems a bit incredible to me, but that was the rumor).
It'll be interesting to see what happens with this Mars laser-comm project!
Steve K.