Table-top electron probe: Extreme UV

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  • Published: Mar 1, 2018
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Table-top electron probe: Extreme UV

NLO probe

After the interaction of a xenon atom with two photons from an attosecond pulse (purple), the atom is ionized and multiple electrons (green balls) are ejected. This two-photon interaction is made possible by the latest achievements in attosecond technology. (Copyright: Christian Hackenberger)

Researchers in Germany have developed new laser technology that can generate attosecond bursts of high-energy photons with unprecedented intensity. The technology allows them to watch observe the interaction of multiple photons from a single pulse with electrons in the inner shell of an atom.

Physicists at the Laboratory for Attosecond Physics (LAP), a joint venture between the Ludwig-Maximilians-Universität Munich (LMU) and the Max Planck Institute of Quantum Optics (MPQ), have succeeded in meeting the conditions necessary to generate ultrashort and ultrabright pulses in the extreme ultraviolet. This potent combination has been searched for by laboratories around the world for at least fifteen years. The new experiments allow the probing of the non-linear interaction of the pulses with an atom's inner electrons in a way that was simply not possible previously. In this setting, non-linear refers to the fact that the interaction involves more than one photon, two in fact.

The technique used to observe these inner electrons in motion uses a pump-probe approach. Electrons within a target atom are initially excited by photons from a pump pulse, and this is followed by the second, ultrashort, high-energy probe pulse of photons. The probe thus illuminates the excited electrons. The team points out that no research group has been able to generate attosecond pulses with the required photon density in the XUV until now.

Laser upscaling

The achievement was made possible by the upscaling of conventional attosecond pulse sources. Laszlo Veisz's team developed a novel high-power laser capable of emitting bursts of infrared light with one hundred times the photon density as conventional systems. In turn, this can then facilitate the generation of isolated attosecond XUV pulses with a similar photon density boost.

In their initial experiments, they pulse-probed atoms of xenon gas. An ion microscope could detect the xenon ions thus generated and to see the interaction of inner electrons with two photons simultaneously.

Multibody solutions

"With two XUV pulses, we would be able to 'film' the electron motion in the inner atomic shells without perturbing their dynamics," explains study leader Boris Bergues. "The electron dynamics in the inner shells of atoms are of particular interest, because they result from a complex interplay between many electrons that interact with each other," Bergues continues. "The detailed dynamics resulting from these interactions raise many questions, which we can now address experimentally using our new attosecond source." For instance, this approach could allow researchers to look at the complex multibody dynamics of electrons in ways not possible previously.

Related Links

Optica 2018, 5, 237-242: "Table-Top Nonlinear Optics in the 100-eV Spectral Region"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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