by Graz University of Technology
https://phys.org/news/2021-07-electrons ... nergy.htmlThe absorption of energy from laser light by free electrons in a liquid has been demonstrated for the first time. Until now, this process was observed only in the gas phase. The findings, led by Graz University of Technology, open new doors for ultra-fast electron microscopy.
The investigation and development of materials crucially depends on the ability to observe smallest objects at fastest time scales. The necessary spatial resolution for investigations in the (sub-)atomic range can be achieved with electron microscopy. For the most rapid processes, however, proceeding within a few femtoseconds (quadrillionths of a second), the time resolution of conventional electron microscopes is insufficient. To improve the time duration of electron pulses, electrons would have to be selected within a shorter time window—in analogy to a camera shutter, which controls the exposure time in photography.
In principle, this temporal selection is possible with extremely short laser pulses through a process called laser-assisted electron scattering (LAES). In this process, electrons can absorb energy from the light field during collisions with atoms of the sample under investigation. "Structural information is provided by all electrons, but those that have a higher energy level can be assigned to the time window in which the light pulse was present. With this method, it is possible to select a short time window from the long electron pulse and thus improve the time resolution," explains Markus Koch, professor at the Institute of Experimental Physics at Graz University of Technology. So far, however, LAES processes have only been observed in the gas phase, despite their investigation for about 50 years.