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
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 . 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 . 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.
- absorption spectroscopy
A team of researchers from the Max Planck Institute for Nuclear Physics in Heidelberg, the Physikalisch-Technische Bundesanstalt in Braunschweig and the University of Aarhus in Denmark demonstrated for the first time Coulomb crystallization of highly-charged ions (HCIs). Inside a cryogenic ... more
When an intense laser pulse interacts with an atom it generates agitation on the micro scale. A rather likely outcome of this interaction is single ionization, where one electron is ejected from the atom. From time to time, however, two electrons can be removed from the atom, resulting in t ... more
Not only birds, fish and even crowds of people show collective movement patterns, motile bacteria also form currents and vortices when their cell density exceeds a certain size. Researchers at the Max Planck Institute for terrestrial Microbiology in Marburg have now been able to show how sw ... more
Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of fat in the liver with an insulin resistance due to causes other than alcohol intake. NAFLD includes a spectrum of liver diseases from simple steatosis (“non-progressive” and reversible) to non-alcoholic steato ... more
A team of neuroscientists and electrical engineers from Germany and Switzerland developed a highly sensitive implant that enables to probe brain physiology with unparalleled spatial and temporal resolution. Now published in Nature Methods, they introduce an ultra-fine needle with an integra ... more
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