(Nanowerk News) The electron microscope gives us insight into the smallest details of materials and can visualize, for example, the structure of solids, molecules or nanoparticles with atomic resolution. However, most matter in nature is not static. They constantly interact, move, and reshape between initial and final configurations. One of the most common phenomena is the interaction between light and matter, which is ubiquitous in materials such as solar cells, screens or lasers. These interactions are dictated by electrons being pushed and pulled by oscillations of light, and the dynamics are extremely fast: light waves oscillate in atthoseconds, one billionth of a billionth of a second.
Until now, it had been very difficult to directly visualize this extremely fast process in space and time, but that is exactly what a team of physicists from the University of Konstanz managed to do. They recorded films with attosecond time resolution in a transmission electron microscope, providing new insights into the function of nanomaterial and meta-atom dielectrics.
They recently published their results in a scientific journal Natural (“Attodetic electron microscopy of sub-cyclic optical dynamics”).
Generation of ultrashort electron pulses
“If you look closely, almost all phenomena in optics, nanophotonics or metamaterials occur on a time scale under one period of light wave oscillation,” explains Peter Baum, professor of physics and head of the Light and Matter Group at the University of Konstanz. “To film the ultrafast interactions between light and matter we therefore need attosecond time resolution.”
To achieve extreme recording speeds, Baum’s research group used the fast oscillations of a continuous-wave laser to convert the electron beam from an electron microscope into a series of ultrashort electron pulses.
In this process, a thin silicon membrane creates periodic acceleration and deceleration of electrons. “This modulation causes the electrons to chase each other. After some time, they turn into a series of ultrashort pulses,” explained David Nabben, doctoral student and first author of the study. Another laser pulse creates an interaction with the sampled object. Ultrashort pulses of electrons are then used to measure the object’s response to the laser beam, frozen in time like in a stroboscope. In the end, the researchers obtained a movie of the process with attosecond time resolution.
Investigation of nanophotonic phenomena
In their study, the scientists present several examples of time-resolved measurements in nanomaterials. Experiments show, for example, the emergence of chiral surface waves that can be controlled by researchers to move in specific spatial directions, or the characteristic time delays between different radiation modes from the nanoantenna. What’s more, scientists not only investigate such surface phenomena, but also film electromagnetic processes inside waveguide materials.
The results are of great interest for further development in nanophotonics, but also demonstrate the very wide application range of the new attosecond electron microscope. “Direct measurement of the electromagnetic function of materials as a function of space and time is not only of great value to basic science, but also opens the way for new developments in photonic or metamaterial integrated circuits,” Nabben summarizes the impact of the results.