Garching, Germany, August 27, 2004--A German-Austrian research team has presented a method of measuring times in the region of a few hundred attoseconds to allow observation of atomic processes on this time scale.
The electromagnetic field of visible light changes direction approximately one thousand trillion (1015) 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 like 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 thousandth of a femtosecond).
The novelty of the new method is that deflection of the electrons is done with a light field - varying millions of times faster - that imparts its effect in space and time immediately on release of the electrons. For this purpose the attosecond X-ray flash irradiating the atoms is supplemented with an intense laser light pulse comprising just a few oscillations. In this manner the successively emitted electrons are detected separately again, but this time not spatially on a screen but alongside one another on the energy scale. The width E and shape of the measured energy distribution of the electrons reflect the duration and evolution of the electron emission, just as their spatial distribution in conventional streak imaging. In this case, however, "deflection" occurs within half a light period, which opens the way to measurement in the attosecond region.
Observation of the motion of electrons deep inside atoms and molecules is thus now within easy reach. For the first time there is now a chance of presenting experimental answers to questions of effective, collective X-ray emission from atoms (X-ray laser) or of creation and destruction of chemical bonds (control of chemical reactions).