idw – Informationsdienst Wissenschaft
Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
Researchers demonstrate a previously unknown effect of electron acceleration in ultrashort laser pulses.
Scientists from the Friedrich-Alexander University Erlangen-Nuremberg (FAU) and the University of Rostock have discovered a groundbreaking effect in which electrons are ponderomotively accelerated by just a single oscillation of a laser pulse. Until now, this effect was only visible with long laser pulses, but it has now been observed using extremely sharp metal needle tips. This discovery could contribute to the development of ultra-fast optoelectronics.
When an intense laser pulse hits an electron at rest, the latter performs a quiver motion with the frequency of the light field. This motion ceases after the pulse and the electron comes to rest again at its original location. If, however, the light field changes its intensity along the electron's trajectory, the electron builds up an additional drift motion with each oscillation, which it maintains even after the pulse. The spatial profile of the light intensity acts like a hill that the electron slides down.
This effect is called ponderomotive acceleration and has been known for decades. However, due to the low spatial dependence of the intensity even in focused light beams, this light-driven sliding effect is notable only for long laser pulses with many oscillations of the field. In a recent study, researchers have now succeeded in detecting a pronounced ponderomotive acceleration during just a single light oscillation. The key trick was to use sharp metallic needle tips, which exhibit an extremely strong spatial variation of the light intensity upon laser illumination.
In the measurements, the released electrons could be assigned to the individual cycles of the light field for the first time. These new findings were recently published in the renowned journal Nature Physics and could contribute to the development of novel ultrafast optoelectronics and the efficient characterization of short light pulses.
In the experiments conducted at the laboratories of Professor Peter Hommelhoff (Friedrich-Alexander University Erlangen-Nuremberg), a special process was used to produce tungsten needles with particularly sharp tips measuring just a few nanometers (1 nm = 10-9 m) in size, which were then illuminated with optical laser pulses with only about three field oscillations.
"Typically, we are particularly interested in the fast electrons released from the nanotips, which we can control precisely with the waveform of the light pulse. It is known that the ponderomotive motion is completely suppressed for sharp tips. Surprisingly, we have now discovered a previously unknown and pronounced stripe structure in the signal of the slow electrons. Our experiments have even revealed an amplification of the ponderomotive effect for the slow electrons," explains Jonas Heimerl.
To compare with the experimental data, the group led by Professor Thomas Fennel (University of Rostock) carried out comprehensive numerical simulations that quantitatively describe the ponderomotive acceleration effect in a single light oscillation and demonstrate the far-reaching implications for the characterization and control of ultrafast electron dynamics.
“Ponderomotive acceleration is usually described as an effect averaged over many light oscillations. A fascinating aspect of our findings is that this can now be used to measure processes on the time scale of a fraction of a light oscillation,” explains Anne Herzig, doctoral student in Thomas Fennel's group.
“Although the basic physics of the near-field induced stripe structures can in principle be explained by classical mechanics, they open up routes to characterizing the quantum effects of the emission process,” adds Anne Herzig. The findings could only be achieved through the excellent interplay of experiment and theory and have the potential to expand the fundamental understanding of photoemission and enable new applications in ultrafast metrology and optoelectronics.
Figure:
Mechanism of ponderomotive acceleration in the near-field: A light field consisting of only a few oscillations releases electrons at the maxima of the field. The localized near-field at a sharp nanotip creates a steep ponderomotive potential hill, which the electrons can slide down. Since electrons released earlier are accelerated for longer, electrons from the individual cycles can be separated from each other by measuring their velocity.
Prof. Dr. Peter Hommelhoff
Tel. +49 9131 85-27089
peter.hommelhoff@fau.de
Prof. Dr. Thomas Fennel
thomas.fennel@uni-rostock.de
Tel. +49 381 498-6815
Website of the Hommelhoff group: https://www.laserphysik.nat.fau.de
Website of the Fennel group: https://www.snp.physik.uni-rostock.de
Originalpublikation:
J. Heimerl, S. Meier, E. A. Herzig, F. López Hoffmann, L. Seiffert, D. Lesko, S. Hillmann, S. Wittigschlager, T. Weitz, T. Fennel und P. Hommelhoff, Attosecond physics in optical near fields, Nature Physics (2025), doi: 10.1038/s41567-025-03093-3
Mechanism of ponderomotive acceleration in the near-field.
Logos: University of Rostock and University of Nürnberg
Criteria of this press release:
Business and commerce, Journalists, Scientists and scholars, Students, Teachers and pupils, all interested persons
Physics / astronomy
transregional, national
Research projects, Research results
English
Mechanism of ponderomotive acceleration in the near-field.
Logos: University of Rostock and University of Nürnberg
You can combine search terms with and, or and/or not, e.g. Philo not logy.
You can use brackets to separate combinations from each other, e.g. (Philo not logy) or (Psycho and logy).
Coherent groups of words will be located as complete phrases if you put them into quotation marks, e.g. “Federal Republic of Germany”.
You can also use the advanced search without entering search terms. It will then follow the criteria you have selected (e.g. country or subject area).
If you have not selected any criteria in a given category, the entire category will be searched (e.g. all subject areas or all countries).
