There’s only one in the field right now, and it being used to detonate unexploded bombs, but The Economist has plenty of speculation as to how the technology might develop:

But wars are not won by defence alone. What people in the business are more coy about discussing is the offensive use of lasers. At least one such system is under development, though. The aeroplane-mounted Advanced Tactical Laser, or ATL, another chemical laser being put together by Boeing and the American air force, is designed to “neutralise” targets on the ground from a distance of several kilometres.

Suggestions that the weapons will also be mounted on giant, three-legged “fighting machines” are being strenuously denied.