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A first experiment with the new "free-electron laser"

December 05, 2002

An international group of scientists has published first experiments carried out using the new soft X-ray free-electron laser (FEL) at the research center DESY (Nature, vol 420, p 482-485 and p 467). Using small clusters of noble gas atoms, for the first time, researchers studied the interaction of matter with intense X-ray radiation from an FEL on extremely short time scales. "We use noble gas clusters as relatively simple model systems to understand fundamental processes which will be important for future investigations of technologically interesting materials or medically important biomolecules " explains Prof. Jochen R. Schneider, research director and head of the Hamburg Synchrotron Radiation Laboratory HASYLAB at DESY.

The free-electron laser at DESY generates very intense laser light at wavelengths below a 100 millionths of a millimeter, a range called soft X-ray radiation. These are the shortest wavelengths ever generated by an FEL. The peak brilliance of this new laser is a thousand times higher than those of the best current light sources in this wavelength range. Moreover, an X-ray flash of the FEL lasts for only a 100 quadrillionths of a second - this is the time scale where chemical bonds form and atoms change their position. Therefore, chemical reactions can be observed directly.

In a first experiment, clusters of the noble gas Xenon were irradiated with the intense laser light. "What happens can be compared to a microscopic fireworks display" describes DESY physicist Dr. Thomas Möller, who leads the cluster experiment. The Bj'¸rn H. Wiik Prize 2002 was recently awarded to Dr. Möller for his scientific work. "When excited by the intense X-ray flashes, the nobel gas atoms emit more and more electrons thus forming a plasma. Partly, even multiply positively charged atoms develop. As a consequence the cluster "explodes", because of the repulsion of the ions". The details of this explosion reveal fundamental principles of the interaction of intense X-ray radiation with matter. These questions can be approached for the first time. Due to the intensity of the radiation from the free-electron laser, a single light flash can manifest considerably more information about the structure of matter than ever before.

A group of scientists from DESY, from the Brazilian science center Laborat'³rio Nacional de Luz S'­ncrotron and from the Russian Joint Institute for Nuclear Research carried out these first experiments with the free-electron laser. The FEL is part of a 100-meter long test facility for the future project TESLA at DESY. This facility is currently upgraded for two purposes: first, to test the TESLA linear collider technology for particle physics; second, to run a more powerful free-electron laser for even shorter wavelength radiation down to 6 nanometers (millionths of a millimeter). From 2004, this unique light source will be available to scientists from all over the world for their experiments. At the same time it will be used as a pilot facility for the TESLA X-ray laser, designed to produce even shorter wavelength X-ray radiation in the range of 0,1 to 1 nanometer.

Deutsches Elektronen-Synchrotron (DESY)