Institute of Applied Physics

The IAP was founded on June 2nd, 1961 as part of the faculty of natural sciences. Today about 56 employees research and teach in four divisions focusing on Biomedical Photonics, Laser Physics, Nonlinear Optics and Microwave Physics.

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Thomas Feurer wird Vorsitzender der Geschäftsführung des Röntgenlasers European XFEL

Der European XFEL Council hat Thomas Feurer, Leiter des Instituts für Angewandte Physik an der Universität Bern, zum Vorsitzenden der Geschäftsführung ernannt. Feurer wird sein Amt am 1. Januar 2024 antreten. Der internationale Röntgenlaser European XFEL wurde 2017 in Schenefeld bei Hamburg in Betrieb genommen. Er erzeugt extrem intensive Röntgenlaserblitze und ermöglicht damit Spitzenforschung auf unterschiedlichen Gebieten.
Thomas Feurer übernimmt ab dem 1. Januar 2024 für eine Amtszeit von zunächst fünf Jahren den Vorsitz der Geschäftsführung von European XFEL. Er folgt auf den Dänen Professor Robert Feidenhans’l, der die Organisation seit 2017 erfolgreich führt und 2024 in den Ruhestand geht. Thomas Feurer wurde 2004 zum Professor für Physik an der Universität Bern ernannt und leitet dort das Institut für Angewandte Physik. Thomas Feurer bleibt weiterhin Professor an der Universität Bern.
Die Schweiz ist – zusammen mit elf anderen Staaten – Gründungsmitglied des European XFEL. Am Paul Scherrer Institut in Villigen (AG) hat die Schweiz einen eigenen Röntgenlaser (SwissFEL), der den European XFEL ergänzt. Durch den parallelen Bau dieser Infrastrukturen konnten Synergien genutzt und Wissen ausgetauscht werden.
Die Nomination von Thomas Feurer stärkt die bereits engen Beziehungen zwischen der Forschungsgemeinschaft in der Schweiz und dem European XFEL sowie dessen Partnerstaaten. Sie ist auch Zeichen für das partnerschaftliche Engagement der Schweiz innerhalb des Europäischen Forschungsraums. Der gemeinsame Bau und Betrieb von Forschungsinfrastrukturen durch die europäischen Staaten bildet eine wesentliche Grundlage für die langfristige Zusammenarbeit, Integration und Vernetzung von Forschenden über Ländergrenzen hinweg.

Excluding Echo Shift Noise in Real-Time Pulse-Echo Speed-of-Sound Imaging

Computed ultrasound tomography in echo mode (CUTE) allows real-time imaging of the tissue speed of sound (SoS) using handheld ultrasound. The SoS is retrieved by inverting a forward model that relates the spatial distribution of the tissue SoS to echo shift maps detected between varying transmit and receive angles. Despite promising results, in vivo SoS maps often show artifacts due to elevated noise in echo shift maps. To minimize artifacts, we propose a technique where an individual SoS map is reconstructed for each echo shift map separately, as opposed to a single SoS map from all echo shift maps simultaneously. The final SoS map is then obtained as a weighted average over all SoS maps. Due to the partial redundancy between different angle combinations, artifacts that appear only in a subset of the individual maps can be excluded via the averaging weights. We investigate this real-time capable technique in simulations using two numerical phantoms, one with a circular inclusion and one with two layers. Our results demonstrate that the SoS maps reconstructed using the proposed technique are equivalent to the ones using simultaneous reconstruction when considering uncorrupted data but show significantly reduced artifact level for data that are corrupted by noise.

Investigation of the Influence of Pulse Duration and Application Mode on Microsecond Laser Microsurgery of the Retinal Pigment Epithelium

Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted
neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD
was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 microsecond duration (wavelength: 532 nm, exposure area: 90 x 90 micrometer^2, radiant exposure: 247 to 1975 mJ/micrometer^2). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 microseconds and 20 microseconds, whereas no cumulative effects were found for pulse durations of 8 microseconds and 12 microseconds applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 microsecond duration in ramp mode.

New Research Bridges the Gap Between Ultrafast Physics and Quantum Magnetism

The exploration of the quantum world presents enduring challenges in our quest to unravel the complexities of intricate phenomena like superconductivity, superfluidity, topological order, and entanglement. These phenomena arise from the interactions among multiple particles in physical systems, commonly known as "many-body" systems.
In the realm of condensed matter physics, quantum magnet materials offer a fascinating avenue for studying complex many-body physics. These materials comprise arrays of interacting quantum spins embedded within crystal solids, manifesting among the most extraordinary and highly entangled quantum effects. Harnessing efficient control over quantum magnetic materials on ultrafast timescales holds strong potential for applications in quantum technology. However, conventional methods based on ultrafast light are impractical for quantum magnets due to the weak interaction with spins and the delicate nature of their quantum phases.
In work led by Dr. Flavio Giorgianni (Nonlinear optics, IAP), which was performed in collaboration with Quantum Criticality and Dynamics group at the Paul Scherrer Institute, researchers have now experimentally demonstrated a new strategy to efficiently drive spin excitations on an ultrafast timescale in a prototypical quantum magnetic material.

The researchers used terahertz light pulses tuned to resonance with vibrations of the atomic lattice – called phonons - achieving a “magnetophononic” excitation of the spin dynamics. When the difference frequency of two phonons matches the spin-mode frequency, it creates a “singlet” excitation in which the fluctuating quantum spins oppose each other, showing no external magnetism and thus remaining hidden from many conventional detection schemes. This method of using phonons as an intermediary introduces a universal mechanism for controlling nonequilibrium quantum magnetic materials on ultrafast timescales, which provides broad potential both for fundamental studies of many-body systems and for applications in areas including optoelectronics, spintronics, and quantum information.

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