X-rays Monitor Electron Density

Michael D. Wheeler

A team at the University of California used picosecond x-ray diffraction to measure the response of GaAs crystal to sudden heating. This could advance efforts to monitor changes in electron density during biological and chemical reactions with femtosecond resolution.

A lidar image of the Bainbridge Island scarp shows the ridge that runs through the upper portion of the land mass. Courtesy of Kitsap Public Utilities District.

For years, researchers have used x-ray diffraction in the form of synchrotron radiation and conventional electron-impact sources to uncover information about the static structure of materials. Often these experiments took place in very large facilities with costly equipment.

Now a team led by Christoph Rose-Petruck has re-created a similar effect using a tabletop picosecond x-ray source. A Ti:sapphire laser producing 30-fs pulses simultaneously heats and tests a GaAs wafer. A beamsplitter diverts a portion of the beam to heat the wafer, while the other part of the beam irradiates a copper wire to create picosecond x-ray pulses. Details of the work appear in the March 25 issue of Nature.