High-Energy Infrared Beams Adapted for Tabletop X-Ray Device

X-ray pulse rendered as colored light waves (JILA, University of Colorado)

Physicists from University of Colorado at Boulder, with colleagues from the U.S., Austria, and Spain, have developed an X-ray system that captures concentrated infrared beams, in a compact device that can fit on a lab table. The team led by Colorado researchers Henry Kapteyn and Margaret Murnane published their findings in the 8 June issue of the journal Science (paid subscription required).

The process developed by the team focuses intense pulses of infrared light — each just a few optical cycles in duration — into a high-pressure gas cell. The researchers then converted part of the original laser energy into a coherent super-continuum of light that extends well into the X-ray region of the spectrum.

Laser beams, which are visible light, are an effective and familiar way to concentrate energy. Kapteyn notes, however, that “the same revolution that happened for visible light sources that made it possible to create laser-like beams of light for widespread use instead of multidirectional light from a light bulb, is only now happening for X-rays.”

The researchers, including colleagues from Colorado’s JILA institute, Cornell University, Vienna University of Technology in Austria, and Universidad de Salamanca in Spain, show that mid-infrared light can undergo a mixing process in high-pressure gas to produce a beam that combines more than 5,000 low-energy mid-infrared laser photons to generate each high-energy X-ray photon. The beam covers a large swath of electromagnetic spectrum and can enable ultra-short pulses as small as 2.5 attoseconds — one attosecond equals one quintillionth of a second, or the time needed for light to travel the length of three hydrogen atoms.

This discovery makes possible X-ray lasers at a minute fraction of the power previously needed, and in turn, a cost-effective device in the lab that can investigate nanoscale phenomena, including activities of a single cell or chemical reaction. “Because X-ray wavelengths are 1,000 times shorter than visible light and they penetrate materials,” says Murnane, “these coherent X-ray beams promise revolutionary new capabilities for understanding and controlling how the nanoworld works on its fundamental time and length scales.”

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