Researchers demonstrate attosecond increase for electron microscopy

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

Electron microscopes provide a deep insight into the smallest 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 interact, move, and reshape all the time. 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, screens or lasers. These interactions – which are defined by the electrons displaced by the field cycles of a light wave – occur at ultra-fast femtosecond time scales (10^-15 seconds) or even attoseconds (10^-18 seconds, a billionth of a billionth of a second). While ultrafast electron microscopy can provide insight into femtosecond processes, it has so far not been possible to visualize the reaction dynamics of light and matter occurring at attosecond speeds.

Today, a team of physicists from the University of Constance and the Ludwig-Maximilians-Universität München have successfully combined a transmission electron microscope with a continuous wave laser to create an attosecond prototypical electron microscope (A-TEM) . The results are reported in the latest issue of Scientific advances.

Modulate the electron beam

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

Ultra-short electron pulses

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 ultra-short electron pulses, shorter than an optical half-cycle of laser light,” explains the 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 specimen of interest. The ultrashort electron pulses then probe the sample and its reaction to laser light. By scanning the optical delay between the two laser waves, the researchers are then able to obtain attosecond resolution images 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 inside the electron microscope rather than having to change the electron source. That means we have a million times more electrons per second, essentially the full brightness of the source, which is the key to any practical application, “Ryabov continues. Another advantage is that the necessary engineering modifications are quite simple and do not require modifications to the barrel. electron.

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

The study is published in Scientific advances.