MIT researchers prove light alone can evaporate water, hinting at new technologies

Water evaporation has been observed for thousands of years, where water turns from liquid to steam. This process takes place across rivers, lakes, and oceans. While seemingly well-understood, MIT's recent findings challenge the notion that heat is necessary for evaporation; light alone can do the job.

An MIT team led by Professor Gang Chen has shown that light, not just heat, can cause water to evaporate. When light hits water, it can directly cause water molecules to transition into the air, an occurrence the researchers call the photomolecular effect. This surprising revelation indicates that heat is not the only trigger for evaporation.

To confirm their unexpected findings, the team conducted 14 different experiments under various conditions, proving that light can cause evaporation. One key discovery was that air temperature above the water didn't increase during evaporation in visible light; it stabilized, demonstrating that heat wasn't responsible. Other factors, such as the light's angle, color, and polarization, also affected the evaporation. Notably, a 45-degree angle with green light showed the strongest effect, even though water absorbs this wavelength minimally.

The authors believe this widespread effect could lead to new practical uses, including energy production and water purification.

Chen sees extensive potential for this discovery. "I think this has a lot of applications. We're exploring all these different directions. And of course, it also affects the basic science, like the effects of clouds on climate, because clouds are the most uncertain aspect of climate models," he says.

"The finding of evaporation caused by light instead of heat provides new disruptive knowledge of light-water interaction," says Xiulin Ruan from Purdue University, not part of the study. It hints at innovative approaches to water desalination powered by solar energy, representing a pioneering leap in scientific knowledge.