Researchers at the SLAC National Accelerator Laboratory, a Department of Energy facility, have found a better way to track valence electrons.

Valence electrons are the atom's outer electrons, which define the material's structure and properties. They move fast and are only a small part of a larger electron pool, making them more difficult to image than they should be. 

Chance Ornelas-Skarin, now a postdoctoral researcher at SLAC, optimized an existing tracking method by mixing X-ray and optical lasers.

Published in the Physical Review X journal, the study shows that combining the short wavelength of X-rays with the long wavelength of optical lasers has enabled the research team to pick out the material's valence electrons efficiently.

In their proof-of-concept experiment, the material used was silicon, which has four valence electrons out of the 14 electrons per atom. Ornelas-Skarin said:

"All the electrons will feel the hard X-rays, but only the valence electrons will feel the optical rays. So, the sum of those frequencies shows us the valence electrons, which we wouldn't be able to see in any other way without the need for theory to fill in the gaps."

The team led by Prof. David Reis from SLAC and Stanford University examined the atomic-level movement of electrons as they oscillated at twice the frequency of the incident laser. They even rotated the orientation of the laser's optical field and tracked variations in how these electrons responded to the light. 

Ornelas-Skarin said:

"With that, we can understand the structure of bonds, which allows us to learn more about the structure and dynamics of materials, giving us much more information about how complicated materials work."

Reis believes that although they used this method only on silicon, it could also be applied to other materials. They would, however, need to refine the technique using different X-ray wavelengths.

Read the full article here to learn more about the new, improved method of tracking valence electrons.

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