Tumult in sluggish electron existence

An international team of physicists has for the first time directly observed the scattering behavior of electrons in a non-conducting material. Their findings could benefit the radiation medicine.
Electrons in non-conductive materials could be said to be inert. As a rule, they stay in their places, deep inside such an atomic network. So there is relative rest in the dielectric crystal lattice. Physicists from the Laboratory for Attosecond Physics (LAP) of the Ludwig-Maximilians-Universität München (LMU) and the Max Planck Institute for Quantum Optics (MPQ) have teamed up with scientists from the Institute of Photonics and Nanotechnology (IFN-CNR). in Milan, the Institute of Physics of the University of Rostock, the Max Born Institute (MBI), as well as the Center for Free-Electron Laser Science (CFEL) and the University of Hamburg, significantly confused. For the first time, researchers have been able to track the interaction between light and electrons in a dielectric, a nonconducting material on time scales of attoseconds (billionths of a billionth of a second).

The researchers sent flashes of light to a glass particle about 50 nanometers thick, which lasted only a few hundred attoseconds and released electrons in the glass. At the same time, the researchers irradiated an intense field of light onto the glass particles, which had only a few femtoseconds (millionths of a billionth of a second) and caused the released electrons to vibrate. In principle, two different reactions of the electrons could occur in the sequence. First they set in motion, then they collide with the atoms from the particle either elastically or inelastically. Between each interaction, the electrons could move only a few angstroms (10-10 meters) due to the dense crystal lattice. "In an elastic collision, as with billiards, the energy of the electron is conserved, only the direction can change, in an inelastic collision the atoms are excited and part of the energy of the electrons is lost, which means a decrease in the electron signal for the experiment. which we were able to measure ", describes Prof. Francesca Calegari (CNR-IFN Milan and CFEL / University of Hamburg) the experiments.

Since it is left to chance whether an interaction is elastic or inelastic, inelastic interactions will inevitably take place over time and the number of purely elastically scattered electrons will decrease. By accurately measuring the oscillation of the electrons in the strong light field, the researchers were able to find that it took on average about 150 attoseconds for elastically repulsive electrons to leave the nanoparticle. "Based on the measured time delay, we were able to determine an inelastic peak time of about 370 attoseconds for the electrons using our newly developed theory and thus time this process in a dielectric for the first time," says Prof. Thomas Fennel from the University of Rostock and Max-Born. Institute in Berlin the analysis of the measured data.

Fig .: A team of physicists measured the time it takes for electrons to leave a dielectric after being excited by ultraviolet light. The measurement (shown in false colors) was the first of its kind in a dielectric and gave a duration of 150 attoseconds (as). From this time, the physicists could determine that inelastic scattering in the dielectric takes on average about 370 as.

The findings of the researchers could now benefit medical applications. With these world's first ultra-short-term observations of electron motion in a nonconductive material, researchers have gained important insights into the effect of radiation in a body similar to human tissue. In the experiments, the energy of the excited electrons is controllable via the light and thus this process can be studied for a broad energy range and for various dielectrics. "Whenever high-energy radiation is applied to tissue, electrons are generated, which in turn transfer energy to the atoms and molecules of the tissue through inelastic collisions, destroying it, and accurate knowledge of electron scattering is important in combating tumors Using computer simulations to optimize treatments so that a tumor is destroyed, but healthy tissue is spared as possible. ", Prof. Matthias Kling describes the importance of the work. In the next step, the scientists want to replace the glass nanoparticles with water droplets in the experiments, in order to investigate the interaction between electrons and the material from which living tissue largely consists.
(Text: Thorsten Naeser)

Original publication

Attosecond chronoscopy of electron scattering in dielectric nanoparticles

L. Seiffert, Q. Liu, S. Zherebtsov, A. Trabattoni, P. Rupp, M. C. Castrovilli, M. Galli, F. Süßmann, K. Wintersperger, J. Stierle, G. Sansone, L. Poletto, F. Frassetto, I. Halfpap, V. Mondes, C. Graf, E. Rühl, F. Krausz, M. Nisoli, T. Fennel, F. Calegari, M. F. Kling

Nature Physics online (2017) 4129