Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Choreography of an electron pair

18.12.2014

The motion of the two electrons in the helium atom can be imaged and controlled with attosecond-timed laser flashes

Physicists are continuously advancing the control they can exert over matter. A German-Spanish team working with researchers from the Max Planck Institute for Nuclear Physics in Heidelberg has now become the first to image the motion of the two electrons in a helium atom and even to control this electronic partner dance.


Electronic pas de deux: Physicists in Heidelberg have filmed the pulsing motion of the electron pair in a helium atom. At 15.3 femtoseconds (fs) the two electrons are close to the nucleus (centre of image) and then move away from it. The colour indicates the probability of finding one electron at position A (vertical axis) and the second electron at position B (horizontal axis) on a line drawn through the atom (along the polarisation direction of the laser). At 16.3 femtoseconds they arrive back at their original position again; they thus move with a beat of around one femtosecond.

© MPI for Nuclear Physics

The scientists are succeeding in this task with the aid of different laser pulses which they timed very accurately with respect to each other. They employed a combination of visible flashes of light and extreme-ultraviolet pulses which lasted only a few hundred attoseconds. One attosecond corresponds to a billionth of a billionth of a second. Physicists aim to specifically influence the motion of electron pairs because they want to revolutionise chemistry: If lasers can steer the paired bonding electrons in molecules, they could possibly produce substances which cannot be produced using conventional chemical means.

Electrons are hard to get a hold of. Physicists cannot determine their precise location in an atom, but they can narrow down the region where the charge carriers are most probably located. When electrons move, this brings about a change to the regions where the electrons have the highest probability of being located. In some electronic states – physicists call them superposition states – this motion manifests itself as a pulsing with a regular beat.

It is precisely this pulsing motion which scientists working with Thomas Pfeifer, Director at the Max Planck Institute for Nuclear Physics, have recorded in a series of images of a helium atom. They observed how the electron pair danced close to the atomic nucleus one moment and slightly moved away from it the next moment. The researchers were not satisfied with the role of mere observers, however, and also actively intervened in the electronic choreography. They laid down the rhythm of the electronic partner dance, so to speak. “The motion of individual electrons in the atom has already been imaged quite often and even manipulated as well,” says Christian Ott, lead author of the study. “We have now achieved it for a pair of electrons which were bound together for a short time.”

When electrons are shifted, molecular bonds can be created

On the one hand, the study of an electron pair is useful for physicists who want to gain a better understanding of how atoms and molecules interact with light as this interaction usually involves two or more electrons. It is useful for chemistry, on the other hand, if they are able to direct pairs of electrons, because the typical chemical bond consists of just such a pair; this means that chemists must always move at least two electrons when they want to create or break a molecular bond.

In order to choreograph and film electrons in a helium atom, the Heidelberg-based physicists sent two laser pulses through a cell with helium gas. It is not only the energy, i.e. the colour of the pulses, which is important here, but also their intensity and the interval between them. The researchers first move the electrons of the helium into the ultrafast pulsing state with the aid of an ultraviolet flash. They succeed only because the duration of this pulse is shorter than one femtosecond (one-millionth part of a billionth of a second), however. This is how long the pair of electrons needs for one cycle of the pulsing motion in which the pair is initially closer to the nucleus, then moves away from it and then returns to the nucleus again.

The researchers then use a weak, visible laser pulse to determine where the electrons are dancing at that particular moment. And by varying the interval between the ultraviolet attosecond pulse and the visible one, they produce a movie of the electronic dance: “Although we do not directly image where the electrons are,” explains Thomas Pfeifer, “the visible pulse provides us with the relative phase of the superposition state.” The phase describes the to and fro of an oscillation, and hence the rhythmic motion of the electron pair. In this case it tells the physicists at which point of their natural pas de deux around the helium atom the electrons are at a given moment.

The team in Heidelberg uses findings from previous research to determine the dance moves. From this existing knowledge they determine where the electrons are when they are not moving. “With the information on the phase which we measured here and our prior knowledge we reconstruct where the electrons are at a given time,” says Pfeifer. He and his colleagues' experimental results are in good agreement with state-of-the art theoretical simulations by their cooperators Luca Argenti and Fernando Martín at Universidad Autónoma de Madrid in Spain, confirming the validity of the experimental and computational methodology.

Intense visible laser pulses change the rhythm of the electronic dance

The Heidelberg-based physicists also rely on these simulations to confirm the second part of their experiments. The visible laser pulse here serves them not only as a camera but also as a pacemaker for the pulsing motion of the electrons. For when they increase the intensity of the pulse, the points in time at which the electrons are close to the atomic nucleus or further away from it shift in time. The researchers also record in an image sequence how the rhythm and thus the choreography of the electronic dance changes.

Thomas Pfeifer and his colleagues have not yet been able to explain all the details which they observe in the experiments with intense laser pulses. They want to change this now with more comprehensive experiments on the effect of the pulses. In future experiments they also want to follow the subsequent fate of the pair of electrons in great detail, for the electronic dance in the superposition state ends with one of the two partners being ejected from the atom, with the consequence that the atom is ionised. These ionisations also play a role in many chemical reactions. A better understanding of such wild two-electron dances could thus tell chemists how a reaction can be steered into the desired direction and product channels. At this point, at the latest, attosecond physics would create new tools for chemistry as well.

Contact

 Dr. Thomas Pfeifer
 
Phone:+49 6221 516-380Fax:+49 6221 516-802

Original publication

 
Christian Ott, Andreas Kaldun, Luca Argenti, Philipp Raith, Kristina Meyer, Martin Laux, Yizhu Zhang, Alexander Blättermann, Steffen Hagstotz, Thomas Ding, Robert Heck, Javier Madroñero, Fernando Martín and Thomas Pfeifer
Reconstruction and control of a time-dependent two-electron wave packet

Dr. Thomas Pfeifer | Max Planck Institute for Nuclear Physics, Heidelberg

Further reports about: Electrons Max Planck Institute Nuclear Nuclear Physics Physicists Planck laser pulses pair rhythm

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>