Progress In The Study Of Rapid Electron Movements With Short Light Pulses

Temporal resolution in the range of attoseconds achieved

When an electron moves in a molecule or a semiconductor, it does so in unimaginably short periods of time. On the way to better understanding such processes, a Swedish-German team led by the physicist Dr. Jan Vogelsang from the University of Oldenburg has now made a decisive advance: the researchers tracked the movement of electrons that were released from crystals of the compound zinc oxide by a laser pulse, simultaneously with a spatial resolution in the nanometer range and a previously unattainable temporal resolution. The team is demonstrating the applicability of a process that could, for example, be used to better understand the behavior of electrons in nanomaterials or new types of solar cells. Researchers from Lund University were involved in the study, which was published in the journal Advanced Physics Research, including this year's Nobel Prize winner in physics, Prof. Dr. Anne L'Huillier.

In the experiments, the team combined a special variant of electron microscopy, known as photoemission electron microscopy (PEEM), with the possibilities of attosecond physics. Researchers use unimaginably short flashes of light to precisely control the movement of electrons and record their subsequent behavior. “You can imagine the procedure as similar to that in photography, when you essentially freeze a fast movement with a flash,” explains Vogelsang. An attosecond is a billionth part of a billionth of a second.

As the team reports, similar experiments had previously failed to achieve the necessary temporal precision to track the movement of electrons. The small elementary particles whiz around much faster than the larger and heavier atomic nuclei. In the current study, however, it was possible to combine the two technologically demanding methods of photoemission electron microscopy and attosecond microscopy without sacrificing spatial or temporal resolution. “We have finally reached the point where we can practically use attosecond pulses to study the interaction of light and matter in detail at the atomic level and in nanostructures,” says Vogelsang.

One of the things that made this advance possible was to use a light source that produces a particularly large number of attosecond flashes per second - in this case 200,000 light pulses per second. Each flash released exactly one electron from the surface of the crystal, so that the researchers were able to study their behavior undisturbed. “The more pulses per second you achieve, the easier it is to extract a small measurement signal from a data set,” explains the physicist.

The necessary technology is available in Anne L'Huillier's laboratory at Lund University (Sweden), where the investigations for the current study also took place. Vogelsang, who conducted research as a postdoctoral researcher in Lund from 2017 to 2020, is currently setting up the process at the University of Oldenburg. In the future, both teams want to continue their investigations and explore the behavior of electrons in various materials and nanostructures.

Since 2022, Vogelsang has headed the attosecond microscopy research group at the University of Oldenburg, which is funded by the German Research Foundation in the renowned Emmy Noether program.