Progress in the study of ultrafast electron dynamics using short light pulses

When electrons move in molecules or semiconductors, their time scale is unimaginably short. The Swedish German team, including Dr. Jan Vogelsang from the University of Oldenburg, has made significant progress in these ultrafast processes: researchers are able to track the dynamics of electrons released on the surface of zinc oxide crystals using laser pulses with nanoscale spatial resolution and previously unattainable temporal resolution.

The relevant paper is titled "Time Resolved Photoemission Electron Microscope on a ZnO Surface Using an Extreme Ultraviolet Attention Pulse Pair" and published in Advanced Physics Research.

Through these experiments, the research team has demonstrated the applicability of this method, which can be used to better understand the electronic behavior of electrons in nanomaterials and new solar cells. Researchers from Lund University in Sweden, including Professor Anne L'Huillier, one of the three Nobel laureates in physics last year, also participated in this study.

Here, this work demonstrates the use of spatial and energy resolved photoelectrons to perform attosecond interferometric measurements on zinc oxide (ZnO) surfaces. The combination of optical emission electron microscopy and near-infrared pump extreme ultraviolet probe laser spectroscopy resolved the instantaneous phase of the infrared field with high spatial resolution. The research results indicate that zinc oxide nuclear energy with low binding energy is very suitable for spatially resolved attosecond interferometry measurement experiments. A significant phase shift of the attosecond beat frequency signal was observed across the entire laser focus, attributed to the wavefront difference between the surface pump field and the probe field.

Figure 1: Characterization of the experimental setup.

In the experiment, the research team combined a special electron microscope, a light emission electron microscope (PEEM), with attosecond physics techniques. Scientists use extremely short duration light pulses to excite electrons and record their subsequent behavior. This process is very similar to the process of capturing rapid motion with a flash in photography.

As reported by the research group, similar experiments have yet to achieve the time accuracy required to track electronic motion. The motion speed of these tiny elementary particles is much faster than that of larger and heavier atomic nuclei. However, in this study, scientists combined the highly demanding techniques of light emission electron microscopy and attosecond microscopy without affecting spatial or temporal resolution.

Figure 2: Spectral results of zinc oxide surface.
Vogelsang said, "Now we can finally use attosecond pulses to study in detail the interaction between light and matter at the atomic level and in nanostructures.".

One factor contributing to this progress is the use of a light source that can generate a large number of attosecond pulse flashes per second - in this case, this light source can generate 200000 light pulses per second. Each flash releases an average of one electron from the surface of the crystal, allowing researchers to study their behavior without affecting each other. The more pulses generated per second, the easier it is to extract small measurement signals from the dataset.

Figure 3: Spatial resolved attosecond interferometry measurement of zinc oxide surface.

The experiment of this study was conducted in Anne L'Huillier's laboratory at Lund University in Sweden, which is one of the few research laboratories in the world with the necessary technical equipment for such experiments.

A similar experimental laboratory is currently being established at the University of Oldenburg. In the future, the two teams plan to continue conducting research to explore the behavior of electrons in various materials and nanostructures.

This work provides a clear approach for high spatial resolution attosecond interferometry measurements in the field of atomic scale surfaces, and opens the way for a detailed understanding of the interaction between nanoscale light and matter.

Source: Sohu