Researchers demonstrate increased attosecond for electron microscopy

A team of physicists from the University of Konstanz and Ludwig-Maximilians-Universität München in Germany achieved an attosecond time resolution in a transmission electron microscope by combining it with a continuous-wave laser, offering new insights into light-matter interactions.

Electron microscopes provide an in-depth view of the finest details of matter and can reveal, for example, the atomic configuration of materials, the structure of proteins or the shape of viral particles. However, most materials in nature are not static and rather interact, move and remodel continuously. One of the most common phenomena is the interaction between light and matter, which is ubiquitous in plants as well as in optical components, solar cells, displays or lasers. These interactions, defined by electrons displaced by the field cycles of a light wave, occur on ultrafast femtosecond time scales (10^-15 seconds) or even attoseconds (10^-18 seconds, one billionth of a billionth of a second). While ultrafast electron microscopy may provide some insight into femtosecond processes, it has not been possible, until now, to visualize the reaction dynamics of light and matter occurring at attosecond rates.

Now, a team of physicists from the University of Konstanz and Ludwig-Maximilians-Universität München has managed to combine a transmission electron microscope with a continuous wave laser to create an attosecond electron microscope (A-TEM) prototype. The results are reported in the latest issue of Advances in science.

Modulation of the electron beam

“Basic phenomena in optics, nanophotonics or metamaterials occur in attosecond times, shorter than a light cycle,” explains Professor Peter Baum, lead author of the study and head of the Light and Matter research group at the Department of Physics of the University of Constance. “To be able to visualize the ultrafast interactions between light and matter requires a temporal resolution less than the oscillation period of the light.” Traditional transmission electron microscopes use a continuous electron beam to illuminate a sample and create an image. To achieve a temporal resolution of one attosecond, Baum’s team uses the rapid oscillations of a continuous wave laser to modulate the electron beam inside the microscope over time.

Ultrashort electron pulses

The key to their experimental approach is a thin membrane that the researchers use to break the symmetry of the optical cycles of the laser wave. This causes the electrons to accelerate and decelerate in rapid succession. “As a result, the electron beam inside the electron microscope is transformed into a series of ultrashort electron pulses, shorter than half the optical cycle of the laser light,” says first author Andrey Ryabov, postdoctoral researcher on the study. Another laser wave, which is separate from the first, is used to excite an optical phenomenon in a sample of interest. The ultrashort electronic pulses then probe the sample and its reaction to the laser light. By scanning the optical delay between the two laser waves, the researchers are then able to obtain one attosecond resolution footage of the electromagnetic dynamics within the sample.

Simple changes, big impact

“The main advantage of our method is that we are able to use the continuous electron beam available within the electron microscope rather than having to change the electron source. This means that we have a million times more electrons per second, basically the full brightness of the source, which is the key to any practical application “, continues Ryabov. Another advantage is that the necessary technical modifications are quite simple and do not require modifications to the electron guns.

As a result, attosecond resolution can now be achieved in a whole range of space-time imaging techniques such as time-resolved holography, waveform electron microscopy or laser-assisted electron spectroscopy, among others. . In the long run, attosecond electron microscopy can help uncover the atomistic origins of light-matter interactions in complex materials and biological substances.

The study is published in Advances in science.