Laser Research

World’s fastest water heater

Print edition : June 22, 2018

After about 70 femtoseconds (quadrillionths of a second) most water molecules have already split into hydrogen (white) and oxygen (red). Photo: CARL CALEMAN, DESY/UPPSALA UNIVERSITY

Scientists at the Centre for Free-Electron Laser Science (CFEL) at DESY, Hamburg, and Uppsala University, Sweden, have used a powerful X-ray laser to heat water from room temperature to 100,000°C in less than a tenth of a picosecond (millionth of a millionth of a second).

The researchers used the X-ray free-electron laser Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory in the U.S. to shoot extremely intense and ultra-short flashes of X-rays at a jet of water. The experimental set-up, which can be called the world’s fastest water heater, produced an exotic state of water, from which researchers hope to learn more about the peculiar characteristics of water. The observations also have practical use for the probing of biological and other samples with X-ray lasers. The findings have been reported in the Proceedings of the National Academy of Sciences (PNAS).

“Normally, when you heat water, the molecules will just be shaken stronger and stronger. At the molecular level, heat is motion—the hotter, the faster the motion of the molecules…. Our heating is fundamentally different,” explains Carl Caleman of CFEL.

“The energetic X-rays punch electrons out of the water molecules, thereby destroying the balance of electric charges. So, suddenly the atoms feel a strong repulsive force and start to move violently.” In less than 75 femtoseconds (millionths of a billionth of a second) or 0.000 000 000 000 075 seconds, the water goes through a phase of transition from liquid to plasma.

“But while the water transforms from liquid to plasma, it still remains at the density of liquid water, as the atoms didn’t have time to move significantly yet,” co-author Olof Jönsson from Uppsala University adds. This exotic state of matter is not found naturally on the earth. “It has similar characteristics as some plasmas in the sun and the gas giant Jupiter, but has a lower density. Meanwhile, it is hotter than the earth’s core.”

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