11-Nov-2019 - Max-Planck-Institut für Kernphysik

Distorted Atoms

In two experiments performed at the free-electron laser FLASH in Hamburg a cooperation led by physicists from the Heidelberg Max Planck Institute for Nuclear physics (MPIK) demonstrated strongly-driven nonlinear interaction of ultrashort extreme-ultraviolet (XUV) laser pulses with atoms and ions. The powerful excitation of an electron pair in helium was found to compete with the ultrafast decay, which temporarily may even lead to population inversion. Resonant transitions in doubly charged neon ions were shifted in energy, and observed by XUV-XUV pump-probe transient absorption spectroscopy.

An international team led by physicists from the MPIK reports on new results for efficient two-electron excitations in helium driven by strong and ultrashort extreme-ultraviolet (XUV) laser pulses [1]. Such doubly excited states are short-lived, decaying in just a few femtoseconds (10⁻¹⁵ seconds) via autoionization: one electron falls back into the ground state while the other one escapes from the atom. To achieve a significant population of this state, the rate of excitation has to be faster than the decay rate. It is like pumping water into a reservoir which has a significant leak.

This experiment has been performed at the Free-Electron Laser in Hamburg (FLASH), which delivers intense XUV laser pulses with a sufficiently short interaction time. Theoretical modelling predicts an efficient excitation of the electron pair by such pulses. Temporarily, the excited-state population may even exceed that of the ground state, creating a population inversion. This laser-controlled quantum dynamics with two active electrons manifests itself in a significant modification of the XUV light absorption, which has been observed in the experiment (see lower part of Figure).

In a second experiment at FLASH, the team around the Heidelberg physicists carried out XUV-pump XUV-probe transient absorption spectroscopy of doubly charged neon ions [2]. Here, the free-electron laser is used both for the production of the ions as well as for the spectroscopy. It reveals a nonlinear coherence spike on a few-femtosecond timescale which relates to the coherence time of a free-electron laser pulse. It thus represents a key step towards the implementation of two- and multidimensional spectroscopy approaches, even for statistically fluctuating free-electron lasers and gas-phase samples. The scientific key result of this experiment was the direct measurement of shifts of atomic energy levels induced by nonlinear interaction with the intense XUV laser.

Altogether, these results open up new routes to explore extreme light-matter interaction and for element-specific quantum control with resonant nonlinear optics at short wavelengths.

Tuning the distortion of specific chemical elements within molecules could, in the future, revolutionize our way of thinking about chemistry.

Facts, background information, dossiers
  • absorption spectroscopy
More about MPI für Kernphysik
  • News

    Weighing an ant on top of an elephant: Quantum jump tipping the balance

    A new door to the quantum world: when an atom absorbs or releases energy via the quantum jump of an electron, it becomes heavier or lighter, according to Einstein’s theory of relativity (E = mc²). However, the effect is minuscule for a single atom. Nevertheless, the team of Klaus Blaum and ... more

    Quantum logic spectroscopy unlocks potential of highly charged ions

    Scientists from the Physikalisch-Technische Bundesanstalt (PTB) and the Max Planck Institute for Nuclear Physics (MPIK) have carried out pioneering optical measurements of highly charged ions with unprecedented precision. To do this, they isolated a single Ar¹³⁺ ion from an extremely hot pl ... more

    The proton precisely weighted

    What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the ... more

More about Max-Planck-Gesellschaft
  • News

    The relationship of proteins

    Proteins control life as one of the most important biomolecules - as enzymes, receptors, signal or structural building blocks. Researchers at the Max Planck Institute (MPI) of Biochemistry have for the first time uncovered the proteomes of 100 different organisms. The selected specimens com ... more

    The Higgs boson and superconductivity

    Without the Higgs mechanism, particles would have no mass. The Higgs boson, which was discovered in 2012, is therefore also referred to as the “God particle”. It arises as an oscillating excitation of the Higgs field, which penetrates the world. Superconductivity displays similar properties ... more

    Weighing an ant on top of an elephant: Quantum jump tipping the balance

    A new door to the quantum world: when an atom absorbs or releases energy via the quantum jump of an electron, it becomes heavier or lighter, according to Einstein’s theory of relativity (E = mc²). However, the effect is minuscule for a single atom. Nevertheless, the team of Klaus Blaum and ... more