German-Austrian research team presents a method of measuring time in the region of a few hundred attoseconds, allowing the observation of atomic processes on this time scale

The electromagnetic field of visible light changes direction approximately one thousand trillion times per second, so that the intensity of the light field varies from zero to maximum faster than a femtosecond (1 femtosecond being one thousandth of a trillionth of a second). By precisely controlling these hyperfast oscillations in a short laser pulse scientists from the Vienna University of Technology and Max Planck Institute for Quantum Optics in conjunction with their colleagues from the University of Bielefeld succeeded in developing the first measuring apparatus: An "ultrafast stopwatch". This apparatus is capable of measuring the duration of atomic processes with an accuracy of less than 100 attoseconds (1 attosecond being one tousandth of a femtosecond). A 250?attosecond X-ray pulse initiates the atomic process to be measured and the attosecond stopwatch at the same time. This new measuring method now allows for the first time observation of ultrafast processes in the electron shell of atoms.

With the most modern microscopes scientists can observe atoms at rest. If, however, the atoms are in motion, very short light pulses are needed to reconstruct the motion from a series of snapshots. Whereas an exposure time of less than a thousandth of a second is sufficient for sharp imaging of a tennis-ball in flight, the light pulses have to be shortened by a billionth, to just a few femtoseconds, in order to record the fastest atomic motions in molecules. Inside the electron shell of excited atoms electrons fly a thousand times faster. They change from one energy state to another typically within 10 to a few 1000 attoseconds and in the process cause atoms originally bound in a molecule to fly apart or emit ultraviolet radiation or X-rays. These processes are of fundamental significance for controlling chemical reactions and synthesising new materials. They could even be applied for designing a versatile X-ray laser.

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