New York /Munich, Germany - September 5, 2022 - An international team of scientists proposes a new ultramicroscope for nanostructures, allowing for the direct and non-invasive measurement of ultrafast processes on attosecond timescales with high spatial and temporal resolution. Metallic nanostructures, consisting of a few thousand atoms, exhibit optical and electronic properties which are not present in extended solid state systems. The interaction of electromagnetic radiation, that is light, with nanoparticles leads to collective, coherent oscillations of electrons, the so-called surface plasmons. A team of scientists from the Georgia State University (Atlanta, Georgia, USA), the Ludwig-Maximilians-Universität (LMU) Munich and the Max Planck Institute of Quantum Optics in Garching (MPQ) have now proposed a new microscope that allows for the first time to resolve the ultrafast dynamics of plasmonic fields with high spatial and temporal resolution, as reported in the science magazine "Nature Photonics". In particular, applications in optical and optoelectronical information processing, transfer, and storage would benefit from a better understanding of these collective excitations. Furthermore, this ultramicroscope would have applications in the spectroscopy of single (bio)-molecules, where nanoparticles act as antennas for light interaction.
Without deeper insight, the makers of colored glass vases in ancient Rome or church windows in the middle ages have already used the properties of metallic nanoparticles to their advantage. The shiny red color was achieved by adding gold dust to the glass melt. The origin of this effect is understood by specialists today: nanoparticles, i.e. particles with extensions in the range from a few to 100 nanometers - less than the wavelength of visible light (ca. 400 - 800 nanometers) - consist of as little as a few thousand atoms. If such a particle is exposed to visible light, the freely moving conduction electrons are displaced by the light's electric field. Since the structure is small, they are not moving very far, but alternate being bunched on one side or the other. This way, the electrons are moving collectively in synchronized coherent oscillations.

Such oscillations have particle character and are called surface plasmons.
The red color of ancient Roman vases and old church windows is based on the absorption of part of the visible light by the gold nanoparticles, which is converted into plasmons. Then the residual light shines in the complementary colors. "Plasmons create very high electromagnetic fields at the nanoparticle and its direct environment," explains Dr. Matthias Kling, Junior Research Group leader at MPQ. "But how these fields are created and how they decay is not understood in detail. The fastest dynamics of the collective motions takes place in only a few hundred attoseconds and belongs to the fastest processes in nature. One attosecond is a billionth of a billionth of a second.

A new method to resolve the dynamics of plasmonic fields with the highest temporal and spatial precision has been suggested by the theoretical physicist Professor Mark Stockman (Georgia State University at Atlanta, Georgia, USA) together with experimental physicists from LMU and MPQ in Germany. In their model, the scientists simulated a geometric assembly of silver nanoparticles on a surface, which are then excited by an - extremely short - few femtosecond pulse. A femtosecond is a millionth of a billionth of a second.

The interaction with the light-pulse -- consisting of only a few oscillation periods -- leads to the formation of plasmonic fields, whose amplitudes and frequencies (between the near infrared and near ultraviolet) depend on the size, shape, and environment of the nanoparticles. The plasmon dynamics is probed by a 170 attosecond, extreme ultraviolet laser pulse incident on the nanosystem that is synchronized with the excitation pulse and releases electrons. The plasmonic fields are monitored by the energy and spatial distribution of these so called photoelectrons as they were - prior to their detection - accelerated by these fields.

"In our suggested approach we combine two techniques, which are by themselves already state-of-the-art: the photoemission electron microscope, also called PEEM, and the attosecond streak camera," explains Professor Ulf Kleineberg from LMU. "This way we obtain a spatial resolution, which is on the order of the dimension of the nanoparticles between a few ten to hundred nanometers, and achieve simultaneously -- due to the use of attosecond light flashes -- the extremely high time resolution in the attosecond domain. The measurement principle lays the foundation to measure the formation and temporal evolution of these fields and to control them by specifically shaped laser pulses in the future."

Generally the nanoplasmonic ultramicroscope would allow for the first direct observation of ultrafast processes in nanosystems, such as the conversion of sunlight into electrical energy. The authors see future applications of the technique particularly in the development of novel devices, in which localized nanoplasmonic fields replace electrons in conventional electronics, i.e. are used for information transfer, processing, and storage. The advantage would be that plasmons in these nanosystems allow for information processing and transfer at much higher frequencies (ca. 100,000 times) as compared to electrons in solid state systems. This way, extremely fast optoelectronic and optical devices for computations and information processing may be realized. [O.M.]

Contact:
Professor Dr. Ferenc Krausz
Chair of Experimental Physics, LMU
Director, Max Planck Institute of Quantum Optics
Tel.: +49-(0)89-32905 612
Fax: +49-(0)89-32905 649
E-Mail:
Web: www.attoworld.de, www.munich-photonics.de

Publication:
"Attosecond nanoplasmonic field microscope", M.I. Stockman, M.F. Kling, U. Kleineberg and F. Krausz Nature Photonics, advance online publication, September 3, 2022

Contact at LMU Munich:
Kathrin Bilgeri
Phone: +49 (0)89 2180-6938
mailto:

 

New York / Munich, Germany - August 21, 2007: This goes way beyond freezing: Only in the last few years have scientists been able to cool atoms close to absolute zero, that is zero Kelvin or -273 degree Celsius. In this state they transform into a so-called Bose-Einstein-condensate with unique properties and can be used for measurements of extraordinary precision. For the first time, scientists at the Ludwig-Maximilians-Universität (LMU) Munich and other European institutions have been able to transfer this cooling method in computer simulations directly to molecules and therefore much more complex systems. In the science journal Physical Review Letters, the team reports how ultra-cold molecules could be generated with a novel application of laser light. The scientists now hope for insights into chemical reactions as well as new interactions and effects. Not only ultra-cold atoms but also molecules close to zero Kelvin are extraordinary research objects. These were previously thought to be too complex to be cooled by optical methods, that is through laser light. Molecules consist of many atoms and therefore show internal degrees of freedom as well as external motion - and cooling essentially means the slowing down of movement. "Internal motion generates unwanted heating effects which cannot be easily avoided", explains team leader Regina de Vivie-Riedle. This explains why it has only been possible to cool atoms and in that state bring them together to form molecules. In contrast, the novel application would allow the simultaneous cooling of external and internal motion. This method combines laser light with an optical resonator, a system consisting of two special mirrors. In the gap between these two mirrors all states of a molecule can be controlled by laser light which reduces motion to a minimum. "Our results are based on modern quantum chemical simulations of a test molecule OH", says de Vivie-Riedle. They show that vibrations and rotations inside the molecule can be cooled down completely. At the same time external motion reaches a temperature of only a few micro-Kelvin. Our approach opens new perspectives for the preparation and control of ultra-cold complex systems."

 

Publication:"Cavity cooling of internal molecular motion", Giovanna Morigi, Pepijn W.H. Pinkse, Markus Kowalewski, and Regina de Vivie-Riedle Physical Review Letters, August 17, 2022 issue doi: 10.1103/PhysRevLett.99.073001

Contact:
Professor Dr. Regina de Vivie-Riedle
Department of Chemistry and Biochemistry, LMU Munich
Tel.: +49-89-2180-77533
Fax: +49-89-2180-77133
E-Mail:

Contact at LMU Munich:
Kathrin Bilgeri
Phone: +49 (0)89 2180-6938
mailto:

Minneapolis, May 31, 2022 -  German University Alliance invited its international partners to celebrate its second anniversary. Dr. Wedigo de Vivanco, Dean of International Affairs, Freie Universität Berlin, and Dr. Stephan Fuchs, Director of International Affairs at Ludwig-Maximilians-Universität (LMU) Munich, spoke about news in the schools' programs, degrees and research opportunities and the universities’ progress in the Excellence Initiative.

What's next at the FU? (presentation by Dr. Wedigo de Vivanco)

LMU excellent (presentation by Dr. Stephan Fuchs)