|MadSci Network: Physics|
In a nutshell, a laser with the right frequency and/or energy can break the bonds that hold ordinary water together. Usually what happens is that the laser excites thermal (heat energy) interaction within the water molecule. This causes the translational kinetic energy of the water to increase. This causes a temperature increase thereby causing the molecule to vibrate faster. This faster and faster vibration will eventually shake the bonds free from each other. Alternatively, each molecule (water included) has a natural resonant frequency that the molecules vibrate with. If the laser is tuned to this frequency then it is possible to excite the corresponding vibrational mode and shake the bond apart.
"Dumping laser energy directly into a chemical bond might seem a sensible approach to getting a clean cut, but experimenters have found that the energy often dissipates too quickly to blow the bond apart. The route taken by a group led by Dietrich Menzel and Peter Feulner at the Technical University of Munich is different, involving excitation of inner core electrons deep in the atomic shell structure. Exciting these electrons leaves core "hole" states, which are immediately filled as outer electrons, fall into them. If these outer electrons are sucked out of the bond by the core hole, the bond vanishes. The trick is to target core electron transitions that somehow lead to the breaking of a selected atom's bonds."
See also: sciencewatch.com
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