Shrinking X-ray absorption spectroscopy down to the benchtop

X-ray absorption spectroscopy is a powerful method used by chemists, biologists, and materials scientists to analyze solids, liquids, and gases. The technique can identify elements and provides information about oxidation states, bonding coordination, and other structural features.

Invariably, the analytical work occurs at synchrotrons because those large facilities are uniquely capable of generating the intense, tunable X-rays needed to make the measurements.

Thanks to an advance in laser spectroscopy, researchers eventually might perform such analyses with compact benchtop lasers (Phys. Rev. Lett. 2018, DOI: 10.1103/PhysRevLett.120.093002). Such a development would allow scientists to bypass the challenges of being approved to work at a synchrotron and traveling to those facilities, of which there are only about 60 worldwide.

To generate benchtop X-rays, Dimitar Popmintchev, Margaret Murnane, Henry Kapteyn, and coworkers at the University of Colorado, Boulder, focus mid-infrared laser light into a waveguide filled with helium at high pressure, ionizing the gas. Interactions between the laser light, ions, and electrons generate X-ray photons via a process known as high harmonic generation.

The team used the roughly 1-keV light to make several types of high-resolution X-ray absorption measurements on organic polymers and thin foils of iron and scandium. They also used the light to probe the “water window,” a spectral region key to studying biological specimens. In the future, the method could track ultrafast molecular processes.