Auger decay following near-infrared ionization of clusters

An inner-shell vacancy in an atom can decay very efficiently via the emission of an Auger electron. Thus far, Auger decay has been observed in atoms, molecules and clusters following the ionization or excitation by light with high photon energies in the extreme-ultraviolet and X-ray regime. Surprisingly, we have discovered Auger decay after the interaction of methane clusters with intense near-infrared laser pulses, even though the photon energy is not sufficient to directly generate an inner-shell vacancy. However, due to very efficient ionization avalanching in clusters, electrons from outer as well as inner shells are removed from their atoms during the laser pulse, and a nanoscale plasma is formed. Subsequent recombination of electrons to outer shells of ions and to high-lying Rydberg orbitals then results in a population inversion of the cluster atoms. By observing a clear peak in the electron spectrum, evidence was provided for the first time that Auger decay is one of the relaxation channels of the highly excited system. In the future, the observed population inversion could be exploited for the development of a table-top X-ray laser.

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Invisible laser pulses push electrons in a quantum swing

Unlike natural light sources such as the sun, lasers have special coherence properties, resulting e.g. in the intriguing observation of interference, where the overlap of two lasers can lead to darkness. The coherence of lasers can also be used to push electrons in a quantum swing inside an atom, meaning that electrons oscillate between two quantum states that lie on different energy levels. Such quantum swings are known as Rabi oscillations and have been observed with low-frequency lasers up to the ultraviolet spectral range. In this paper, we show that Rabi oscillations can be driven in an argon atom by an intense laser pulse in the extreme-ultraviolet spectral range, which is invisible for the human eye. By using a second laser pulse, the ultrafast oscillation of electrons between the ground state (the lowest energy level) and an excited state (at a higher energy level) is traced directly in the time domain, showing that it takes place within tens of femtoseconds (corresponding to 10^-14 seconds). Our results pave the way towards multi-photon coherent control techniques in the extreme-ultraviolet range, allowing extension to situations where interactions between electrons play a role, or more complex systems including molecules.

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Fast electrons at long wavelengths

Efficient electron acceleration was observed in clusters induced by a laser field at 1.8 μm that consisted of only two optical cycles. In this regime that is dominated by electronic rather than nuclear dynamics, clear signatures of direct electron emission were observed as well as rescattering of electrons that gain additional kinetic energy during laser-driven collisions with ions and with the cluster potential. The results, which were obtained at the Imperial College London, promise efficient particle acceleration in clusters at mid-infrared and terahertz wavelengths.

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Bernd Schütte receives ISUILS award

Bernd Schütte has received the 7th ISUILS Award for Young Researchers. This prize is sponsored by the Japan Intense Light Field Science Society and was awarded at the 15th International Symposium on Ultrafast Intense Laser Science, currently taking place in Cassis in the South of France. Bernd Schütte has received this award for his work on ultrafast cluster dynamics during the past few years.

Workshop impressions

The second workshop on “Ultrafast Cluster Dynamics” took place from August 23-24 at the Max-Born-Institut, and was organized together with the TU Berlin. Our 40 guests presented 14 exciting posters and 9 talks, which resulted in many lively discussions. A lot of new fascinating results have been obtained since the last workshop that took place 2 years ago in Rostock. We are already looking forward to the next edition of this workshop taking place in Freiburg in 2 years!



Summer Workshop “Ultrafast Cluster Dynamics”

The second summer workshop on “Ultrafast Cluster Dynamics” will take place on August 23-24 at the Max-Born-Institut. Following the first edition organized by Thomas Fennel in Rostock in 2014, this workshop will be organized by Bernd Schütte in collaboration with Daniela Rupp and Maria Krikunova from the TU Berlin. We expect about 45 participants from Germany, but also from abroad. In addition to 9 talks about nonlinear cluster dynamics, we will have 14 interesting poster presentations. Please contact the organizers for more information.