Heat doesn't really exist at an individual particle level, it only describes the average kinetic energy of a large number of particles. "Normal" evaporation occurs because all the water molecules are jiggling around fast enough that sometimes some get knocked off at the top and fly away. The theory from this paper says that light can strike a single water molecule just right that it breaks off without help from the others.

Saying this is "without heat" means that the light isn't simply increasing the average kinetic energy at the top of the water and speeding up the rate of "normal" evaporation. They think it's specifically acting on a single molecule at a time.