From the BBC:
The prototype weapon was demonstrated at the Moody Air Force Base in Georgia.
A beam was fired from a large rectangular dish mounted on a Humvee vehicle.
The beam has a reach of up to 500m (550 yds), much further than existing non-lethal weapons like rubber bullets.
It can penetrate clothes, suddenly heating up the skin of anyone in its path to 50C.
But it penetrates the skin only to a tiny depth – enough to cause discomfort but no lasting harm, according to the military.
A Reuters journalist who volunteered to be shot with the beam described the sensation as similar to a blast from a very hot oven – too painful to bear without diving for cover.