Group meeting, online.
Sambit Mitra will give a talk on his project progress.
Group meeting, online.
Lina Hedewig will give a talk on her project progress.
Controlling strong electromagnetic fields on nanoparticles is the key to triggering targeted molecular reactions on their surfaces. Such control over strong fields is achieved via laser light. Although laser-induced formation and breaking of molecular bonds on nanoparticle surfaces have been observed in the past, nanoscopic optical control of surface reactions has not yet been achieved. An international team led by Dr. Boris Bergues and Prof. Matthias Kling at Ludwig-Maximilians-Universität (LMU) and the Max Planck Institute of Quantum Optics (MPQ) in collaboration with Stanford University has now closed this gap. The physicists determined for the first time the location of light-induced molecular reactions on the surface of isolated silicon dioxide nanoparticles using ultrashort laser pulses.
A nanoparticle in the field of a femtosecond laser pulse with tailored waveform and polarization. The controlled enhancement of the field in specific nanoscopic regions of the nanoparticle (yellow spots) induces site-selective photochemical reactions of the molecules adsorbed on the surface. Imaging of the molecular fragments emitted from these regions enables all-optical control of the reaction sites with nanometer resolution. Illustration: RMT.Bergues
Journal: Optica 9, 551 (2022)
Dr. Boris Bergues
Head of the Strong-Field Dynamics Group
Laboratory for Attosecond Physics
LMU Munich / Max Planck Institute of Quantum Optics
Tel.: (+ 49 89) 32905 – 595
Group meeting, online.
Ritika Dagar will give a talk on her project progress.
Future electronics will be fast. It could be driven at the frequencies of light waves. This implies that the switching speeds would be roughly 100,000 times faster than today. The development of electronics driven by light requires a detailed characterization of the light waves’s electromagnetic fields. Modern so-called field-sampling methods allow for probing the temporal evolution of a light field. While these techniques have been established, a complete and detailed understanding of their underlying mechanism has been lacking. Researchers from the Ultrafast Electronics and Nanophotonics group have now uncovered what exactly happens during the sampling of light fields and how their interaction with matter induces measurable currents in electronic circuits.
Light is a fascinating phenomenon of nature. It is incredibly fast and its electromagnetic field varies with extremely high frequencies. In the visible spectral range, light oscillates with nearly one petahertz (one thousand trillion oscillations per second). This property can be exploited in technology to drive future electronics with the help of the light fields, making it 100,000 times faster than today.
Sophisticated technologies, however, are required in the first step to precisely capture and control these ultrafast oscillations. This is enabled by so-called field-sampling methods. Short laser pulses ionize air near a metal electrode. Thereby, charge carriers are released, which induces currents in the electrode. The direction and strength of the electric current depend on the exact form of the light field, which enables its control. In previous studies, however, it has remained unclear how exactly the generated charge carriers determine the measured current. Moreover, there has been no possibility so far to predict the expected current quantitatively.
Johannes Schötz and coworkers have now uncovered this mechanism. With the help of experimental studies and numerical calculations, they were able to quantitatively model the process. As Johannes explains: “the study has shown that scattering and charge interaction of the generated charge carriers play an essential role in the formation of the macroscopic signal via ultrafast current generation in gases”.
In particular, the study has revealed how the strength of the generated signals can be increased by an order of magnitude. This will help further increase the sensitivity and accuracy of field sampling measurements and is an important step towards novel opto-electronic applications, paving the way to future light-field-controlled electronics.
Journal: Nature Communications 13, 962 (2022)
A strong few-cycle laser pulse leads to strong-field ionization of gas atoms and molecules. The motion of electrons (green) ejected from the atoms and molecules by the light induces a current in the nearby electrode. The process is influenced by the charge interaction between the charge carriers as well as by electron scattering. Illustration: RMT.Bergues
If physicists want to learn more about the dynamics of electrons in solids, they probe them with electromagnetic fields. A particularly powerful method is transient field-resolved spectroscopy. When a laser pulse excites electrons in a solid, its transmission or reflectivity changes. Transient field-resolved spectroscopy permits to monitor these changes after the excitation in the waveform of a sampling light field. Experiments so far, however, concentrated on frequency ranges below 50 terahertz.
Neuhaus and coworkers have now extended transient field-resolved reflectometry to frequency ranges of up to 100 terahertz, doubling the maximum frequency. The physicists could furthermore achieve repetition rates in the megahertz region in the measurements. They excited semiconductors with near-infrared laser pulses (at 800 nanometer wavelength), which lasted only for a few cycles in the femtosecond range. “The advantage of measurements in this extended frequency range is that it is free of other resonances. This permits to accurately monitor the response of free electrons in the materials”, explains Marcel Neuhaus, first author of the study. This way, the technique provided a time resolution of electron dynamics in solids below 10 femtoseconds.
By the extended frequency range the physicists studied dynamics of free charges in the semi-conductors germanium and gallium arsenide in a resonance-free range and could among other things observe, how electrons scatter between the different energy minima in the conduction band, the so called valleys. This allowed them to draw conclusions how the electrons influence each over in their scattering dynamics.
“The demonstrated field-resolved transient reflectometry at frequencies of 50-100 terahertz paves the way to studies of a broad range of intramolecular dynamics, including in molecular/organic electronics”, Prof. Kling explains. He adds: ”In the future, the new frequency range might enable measurements with high sensitivity to molecular vibrations in organic and novel 2D materials.”
Journal: Optica 9, 42 (2022)
A near-infrared pulse (blue) excites a semiconductor. The unfolding ultrafast dynamics is interrogated by field-sampling spectroscopy, where changes to the waveform of a reflected mid-infrared light field (red) are recorded. Illustration: RMT.Bergues
Group meeting, online.
Prof. Agapi Emmanouilidou will give a talk about her newly developed triple ionization model.
Group meeting, online.
Johannes Schötz will give a dry run for his defense talk.
The Ultrafast Imaging and Nanophotonics team, led by Prof. Matthias Kling, in collaboration with the American University Sharjah, reports a new route to the formation of trihydrogen ions (H3+). The route involves a bimolecular reaction between water molecules adsorbed on nanoparticle surfaces, a situation that closely mimics irradiated ice and ice/dust particles in outer space. All routes identified so far involved organic molecules, which cannot exist under high-energy irradiation in space. The unprecedented generation of H3+ was enabled by “engineering” a suitable reaction environment comprising water-covered silica nanoparticles exposed to intense, femtosecond laser pulses.
Trihydrogen ions are arguably the most important triatomic species from the perspective of generating living matter in the universe. Such ions have hitherto not been possible to generate using conventional techniques of chemical synthesis. Their significance stems from their involvement in the production of many organic compounds in the universe and H3+ ions are regarded as an important precursor for the origin of life. The studies explore a new mechanism for the production of H3+ that mimics the conditions in outer space and, thus, provides new insights into the process that governs its creation and, consequently, the beginning of life in the universe. Furthermore, the new approach has the potential to be extended to the production of other new molecules that can have significant biological and environmental applications in terrestrial and non-terrestrial situations.
Physicists of the research group “field resolved nano spectroscopy”, led by Prof. Matthias Kling (left, together with Philipp Rosenberger) of the Ludwig-Maximilians-Universität, found a new route to the formation of trihydrogen ions (H3+) triggered by strong laserpulses.
Picture: Thorsten Naeser
Prof. Matthias Kling
Ultrafast Imaging and Nanophotonics, attoworld-team
Am Coulombwall 1
At this year’s Max Planck School of Photonics Spring School Conference, Najd Altwaijry won a poster award. Her poster, titled: “Small, cheap method to sample electric fields up to 1PHz” included a 5-min video and explained the technique of “Nonlinear Photoconductive Sampling”. Using this technique, the team managed to sample an extremely short pulse (2,8fs) centred at 450 nm using a synthesised waveform from a three channel synthesiser.