The laser enters new dimensions
From zero to 200 kilometres an hour in a millionth of a billionth of a second: that’s a world record – at least for neutral particles. “What really surprised us in our experiments was that neutral particles could reach such a tremendous acceleration through the electric field of a laser,” confessed Ulrich Eichmann at the Max Born Institute (MBI) in Adlershof. The science magazine Nature even presented these results on the front cover of its October 2009 issue.
Actually, electric fields affect only electric charges. The helium atoms Ulrich Eichmann and his colleagues at the Max Born Institute were experimenting with are however outwardly neutral: the positive charges of the atomic nucleus and the negative charges of the electron shells cancel each other out. The physicists discovered that bombarding atoms with ultra short laser pulses shifted some of their electrons to much higher orbits, where they oscillate at an extreme speed. And this in turn causes them to be affected by the ponderomotive force of the laser light’s inhomogeneous electric field, forcing them into even higher orbits. And because they are still bound to the atomic nucleus they simply drag it with them. In this manner the laser bombardment ultimately drives the whole atom.
“With specifically modulated laser light we might be able in future to position atoms very quickly and very precisely on a surface or control chemical reactions there,” concluded Eichmann. However, applications like these are only of secondary interest to the researchers at the Max Born Institute. What they are primarily interested in are the fundamental processes, for instance the structural memory of water or other materials. “At the same time fundamental scientific questions are constantly being stimulated with the targeted progress of the laser technology we need,” said Thomas Elsässer, Managing Director of MBI.
For instance the researchers have managed to make the laser pulses even shorter and their electric fields even stronger. With constantly shorter snapshots they can observe extremely fast processes that take place in nature – for instance chemical reactions or charge transfer in optoelectronic semiconductors. The European Research Council (ERC) awarded Elsässer a 2.49 million Euros advanced grant for the research of extremely fast processes that determine the properties of hydrogen bonds in molecular systems.
The expertise of the Max Born Institute in this field has opened the doors to the newly founded Berlin Laboratory for innovative X-ray Technologies BLiX. In collaboration with the University TU Berlin this laboratory will be providing other research institutes and companies with the latest X-ray technologies. The priority is given not only to the provision of services. Also companies should be in a position to develop prototype equipment into their own products and to market these.
Dr. Uta Deffke