An X-ray beam appears as a thin blue beam at the European X-Ray Free-Electron Laser Facility

A X-ray beam, such as this one at the European XFEL facility in Schenefeld, Germany, can be used to probe materials at an atomic scale. Credit: European XFEL

Optics and photonics

X-ray pulses lasting quadrillionths of a second march in step

Method produces ultra-bright bursts of uniform X-rays that could help researchers to peer inside living cells.

A new technique could improve the performance of a class of light sources that is revolutionizing materials science.

X-ray free-electron lasers (XFELs) produce brilliant X-ray pulses as short as a few quadrillionths of a second. These brief bursts help to capture fast-moving molecular interactions within a sampled material.

The pulses are made by passing a beam of electrons through a magnet array. This coaxes the electrons into emitting radiation. In one technique, an ultraviolet ‘seed’ laser is trained on the electron beam travelling through a short array of magnets, and a separate array helps to amplify the electrons’ output of radiation at the desired, X-ray frequency. But this amplification process also amplifies imperfections in the electron beam.

Primož Rebernik Ribič and Enrico Allaria of Elettra Synchrotron Trieste in Italy and their colleagues demonstrated an alternative technique that uses two sets of seed lasers. This compresses electrons that emit radiation at one particular X-ray frequency into a tight bunch, creating a powerful pulse of X-rays that are more uniform in frequency than those generated by conventional XFELs.

The technique could help researchers to peer inside living organisms.