Laser-Generated X-Rays Help Scientists Watch Atoms Move

SAN DIEGO, Calif., March 30 -- A group of researchers at the University of California-San Diego has devised a laser-based method for peering into the high-speed world of atoms and directly observing their movement. Using ultra-fast pulses that produce x-rays from a simple copper wire, the Wilson Group at UCSD's Department of Chemistry and Biochemistry observed atomic motions inside crystals of gallium arsenide. The experiment is described in the March 25 issue of Nature.
To achieve the result, the group directed 25 fs pulses to send a very fast sound pulse deep into the crystal. At the same time, the laser was directed onto a copper wire, which produced extremely short duration x-ray pulses. These pulses, arriving at chosen times after the atoms of the crystal started to move, diffracted from the moving atoms to generate a movie of the moving sound pulse. This movie shows what the atoms in the crystal are doing with subatomic position accuracy and trillionths of a second time resolution.