Attosecond physics: motion inside atoms

The most modern microscopes allow research scientists to observe single atoms in their rest state. If, however, atoms are moving, very short light pulses are needed to allow the motion to be reconstructed from a series of snapshots. Whereas an exposure time of less than a thousandth of a second is sufficient to make a sharp image of a tennis ball in flight, the light pulses have to be shortened a billionfold to just a few femtoseconds in order to record the fastest atomic motions in molecules. Inside the electron sheath of excited atoms electrons move a thousand times as fast. They change from one energy state to another in a time of typically 10 to 1000 attoseconds. Atoms originally bound in a molecule then fly apart or transmit ultraviolet radiation or X-radiation. These processes are of fundamental importance for controlling chemical reactions and synthesising new materials. They might even be applied to designing a handy X-ray laser.