Atom makes hologram of itself
Researchers from the FOM institutes AMOLF and Rijnhuizen are the first in history to have made a hologram of an atom by using its own electrons. They did this using the unique properties of FELICE, Rijnhuizen's new free electron laser for intracavity experiments. Furthermore, together with an international research team, the researchers have demonstrated that both the electron and the remaining ion are 'stored' in the hologram. This discovery could lead to a new additional technique to unravel processes that take place over an extremely short timescale, and it could also provide insights into important chemical reactions that occur in the world around us. For FOM PhD student Ymkje Huismans this is a superb first publication as principal author: Science published the research results online on 16 December.
Holography with tunnelled electrons
Most people know about holography in the form of the 'rainbow pictures' in their credit card and images that appear to be three dimensional, but in reality are not. A hologram is made by splitting a coherent beam of light or electrons in two. One of the beams illuminates the object, the second beam does not. If both beams are brought back together again they form an interference pattern, in which all of the information about the object is stored.
Huismans and her colleagues used this idea to store information about atoms. They used FELICE, to ionise atoms, and the electrons released were subsequently used to produce a hologram. The first step was to make a coherent source of electrons at some distance from the ion. The atoms were ionised with infrared laser light from FELICE. Whenever the field of the laser is strongest, an electron is released at a distance 30 times that between the innermost electron and the nucleus. Furthermore, this 'tunnel ionisation' has the useful property that the electrons released always have the same phase and are therefore coherent.
Once this coherent source of electrons had been made it had to follow two different parts. This happens automatically if the electron is released when the electric field of the laser is still present. Then the laser ensures that the electrons oscillate towards and away from the ion. This results in some of the electrons colliding with the ion and 'illuminating' it, while other electrons follow a different path and do not collide. When all of the electrons come back together again they form an interference pattern, just like in a traditional hologram. The outcome is a hologram of the atom produced by its own electrons.
Rapid movements in the hologram
Together with researchers from Russia, Germany, England and the US, the measurements were simulated in theoretical models. These revealed that the rapid movements of both the electrons and the remaining ion are stored in the hologram. The first techniques to measure this rapid movement with so-called attosecond (10-18s) pulses have only been developed within the last ten years. Holography in atoms is an additional technique that allows researchers to unravel, understand and possibly guide chemical processes at the most basic level on an attosecond timescale. It is an incredibly valuable technique because until recently these movements could not be measured directly, even though they form the basis for all chemical reactions in the world around us. Being able to measure these movements is therefore vital to understanding these processes.
Information
FOM Institute AMOLF.
FELICE is part of the international research facility FELIX on the FOM-Institute for Plasma Physics Rijnhuizen.
Reference: DOI 10.1126/science.1198450 .
Contact
Ymkje Huismans, (020) 754 71 66.
Prof.dr. Marc Vrakking, +49 1515 715 34 46.