Lightwave-controlled nano accelerator opens up new perspectives

Extremely short electron packets are the key to many new applications such as ultrafast electron microscopy and laboratory-scale free-electron lasers. A team of physicists from the University of Rostock, the Max Born Institute in Berlin, the Ludwig-Maximilians-University Munich and the Max Planck Institute for Quantum Optics in Garching has now shown how electrons with the help of laser light cross only a few Nanometer-sized silver particles can be accelerated extremely strong and controlled. Particularly crucial for possible applications is that the observed acceleration in the form of a nanoscale swing-by-maneuver known from space flight can be controlled with the waveform of the laser field. This could allow a purely optically controlled generation of electron pulses on the attosecond time scale.

Substituting metal clusters, ie tiny metallic nanoparticles of only a few thousand atoms, with intense laser light, the electrons moving in the particle are excited into a collective rocking motion. When using a suitable light color, a resonant excitation is possible, which leads to an extreme rocking of the electron cloud and thus causes a multiple amplified electric field in the particle cluster. In the experiment conducted at the Institute of Physics in Rostock, the team headed by Prof. Thomas Fennel has now made targeted use of this plasmonically enhanced near field. Using so-called two-color laser pulses, the scientists modified the plasmonic fields via the phase angle of the light field in such a way that electrons can be controlledly accelerated by flying through the nanoparticle in just one optical oscillation by means of a centrifugal effect. The experimentally observed findings of the scientists, explained in detail by a theoretical model, have now been published in the journal Nature Communications.

For the first time, it has been possible to control electronic processes in clusters with the aid of the laser light waveform. For both the experiments and the theory, the clusters, which are only a few nanometers in size, are ideal model systems for the investigation of new physical effects in the light-matter interaction of nanostructures. "In our experiment we were able to show that the electrons in the nanospeed accelerator are within can absorb energy amounts of up to one kilo-electron volt in an optical period, which corresponds to an increase of more than one order of magnitude in comparison to the strong-field ionization of atoms ", explains Dr. med. Josef Tiggesbäumker from the Institute of Physics in Rostock, who together with first author Dr. Ing. Johannes Passig and the team around cluster physicist Prof. Karl-Heinz Meiwes-Broer developed the experimental apparatus for the experiments. "The acceleration of the electrons by means of near-field assisted forward scattering can be switched via the light waveform with attosecond precision (1 attosecond = 1 billionth of a billionth of a second)," explains Prof. Matthias Kling from the Ludwig-Maximilians-Universität and the Max-Planck Institute for Quantum Optics in Garching, which has provided the technology for generating the phase-controlled pulses. "Controlling solely through the laser light used for acceleration opens up completely new avenues in the field of currently intensively researched light-based particle acceleration," summed up Heisenberg Fellow Fennel, who is currently researching at the University of Rostock and the Max Born Institute Berlin and the idea developed for the experiment. The researchers are now planning to implement the acceleration principle in follow-up studies in a multi-stage scenario in order to investigate their possible use in laser-driven lattice accelerators.

Original publication

Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters

J. Passig, S. Zherebtsov, R. Irsig, M. Arbeiter, C. Peltz, S. Göde, S. Skruszewicz, K.-H. Meiwes-Broer, J. Tiggesbäumker, M. F. Kling, T. Fennel

Nature Communications 8 (2017) 1181/1-7