Allgemeines Physikalisches Kolloquium
im SS 2024
Donnerstag, 16 Uhr c.t. Ort: HS 2, IG 1, Wilhelm-Klemm-Str. 10, 48149 Münster
11.04.2024 Prof. Stefan Karpitschka
Viscoelastic Contact Dynamics in Soft and Living Matter
The contact dynamics of soft and living materials ubiquitously determine their mechanical interactions experienced in everyday life or technological applications. In this talk, I will present our recent progress on two types of dynamical contact mechanics problems: (i) Dynamical wetting of soft materials, which has recently gained significant interest in the soft matter community, allows to probe the response of soft solids to virtually infinitely sharp line tractions. It turns out that, on such small scales, solid surface tension and poroelastic phenomena cannot be ignored, leading to an intricate coupling of elastic, osmotic, and capillary forces. (ii) Gliding motility of filamentous cyanobacteria, for which no comprehensive explanation exists to date, relies on direct contact of the bacteria with solid surfaces. Harnessing mechanical instabilities, we could measure the forces involved in gliding motility on the scale of individual filaments and show that this type of motility requires adhesion. We expect these findings to be relevant far beyond cell motility research as these organisms belong to the oldest known forms of life on earth and played a key role in the oxygenation of our atmosphere, and today their giant blooms pose major ecological and economical challenges.
18.04.2024 Prof. Pratika Dayal
The emergence of galaxies in the first billion years: implications for reionization, cosmology and gravitational wave astronomy
Galaxy formation in the first billion years marks a time of great upheaval in our cosmic history: the first sources of light in the Universe, these galaxies ended the 'cosmic dark ages' and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of 'cosmic reionization'. The past few years have seen cutting-edge instruments such as the James Webb Space Telescope (JWST) provide tantalising glimpses of such galaxies assembling in an infant Universe. Puzzlingly, these observations are also yielding a sample of unexpectedly numerous and large black holes (up to a 100 million solar masses) within the first 600 million years, posing an enormous challenge for galaxy formation models. I will show how this data is providing an unprecedented opportunity to pin down the reionization state of the Universe in addition to providing an unrivalled resource for understanding the reionization topology in the forthcoming era of 21cm cosmology. I will also show how these early systems provide a powerful testbed for Dark Matter models beyond "Cold Dark Matter". Finally, I will try to give a flavour of the gravitational wave event rates expected from such early black holes in the Laser Interferometer Space Antenna Array (LISA) era.
25.04.2024 Prof. Reinhard Kienberger
Attosecond science – from the beginning to measuring electron dynamics in molecules, solids and layered systems
The generation and measurement of single isolated attosecond pulses in the extreme ultraviolet (XUV) at the beginning of this century has recently been awarded with the Nobel Prize in Physics [1]. This talk will give a historic review since the beginning of attosecond science and its impact on the understanding of electronic processes on the attosecond timescale.A pump/probe technique, “attosecond streaking” [2], was used to investigate electron dynamics on surfaces and layered systems with unprecedented resolution. Photoelectrons generated by laser based attosecond extreme ultraviolet pulses (XUV), are exposed to a dressing electric field from well synchronized few-cycle infrared (IR) laser pulses. The energy shift experienced by the photoelectrons by the dressing field is dependent on the delay between the XUV pulse and the dressing field and makes it possible to measure the respective delay in photoemission between electrons of different type (core electrons vs. conduction band electrons). The information gained in such experiments on tungsten [3] triggered many theoretical activities leading to different explanations on the physical reason of the delay. Attosecond streaking experiments have been performed on different solids [4,5], layered structures and liquids, resulting in different delays – also depending on the excitation photon energy. These measurements lead to a stepwise increase of the understanding of different physical effects contributing to the timing of photoemission. In this presentation, an overview on the different physical contributions to attosecond time delays in photoemission will be given. The “absolute” time delay, i.e. the delay between the instant of ionization and the emission of a photoelectron will be discussed and latest measurements will be presented.[1] M. Hentschel*, R. Kienberger* et al., Nature, 414, (2001)
[2] R. Kienberger et al., Nature 427, 817 (2004)
[3] A. Cavalieri et al., Nature 449, 1029 (2009)
[4] S. Neppl et al., Nature 517, 342 (2015)
[5] M. Ossiander et al., Nature 561, 374 (2018)
02.05.2024
16.05.2024 CRC1459
Vortragsankündigung
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06.06.2024 Prof. Thomas Gehrmann
Vortragsankündigung
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13.06.2024 Prof. David Mapaung
Brillouin Optomechanics in Photonic Integrated Circuits
Stimulated Brillouin scattering (SBS) is a coherent optomechanical interaction between light and gigahertz acoustic waves that can unlock promising technologies including narrow-linewidth lasers, microwave photonic signal processing, and on-chip nonreciprocal light propagation. Recently, SBS has extensively been studied in integrated waveguides. However, many implementations rely on complicated fabrication schemes, using suspended waveguides, or non-standard materials. The absence of SBS in standard and mature fabrication platforms prevents large-scale circuit integration and severely limits the potential of this technology. In this talk, I will focus on our recent results on enhancement of SBS in scalable integration platform including silicon nitride [1-3] and thin-film lithium niobate [4] and I will discuss the potential applications of this technology.
[1] R. Boter, K. Ye, Y. Klaver, R. Suryadharma, O. Daulay, G. Liu, J. van den Hoogen, L. Kanger, P. van der Slot, E. Klein, M. Hoekman, C. Roeloffzen, Y. Liu, and D. Marpaung
Guided-acoustic simulated Brillouin scatering in silicon nitride photonic circuits
Science Advances, vol. 8, no. 40, p. 2196, Oct. 2022[2] R. Boter, Y. Klaver, R. te Morsche, B. L. Segat Frare, B. Hashemi, K. Ye, A. Mishra, R. B. G. Braamhaar, J. D. B. Bradley, and D. Marpaung
Simulated Brillouin scatering in tellurite-covered silicon nitride waveguides
arXiv:2307.12814, Jul. 2023[3] K. Ye, Y. Klaver, O. A. Jimenez Gordillo, R. Boter, O. Daulay, F. Moriche, A. Melloni, and D. Marpaung
Brillouin and Kerr nonlinearities of a low-index silicon oxynitride platform
APL Photonics, vol. 8, no. 5, p. 51302, May 2023[4] Ye, Kaixuan, H. Feng, Y. Klaver, A. Keloth, A. Mishra, C. Wang, and D. Marpaung
Surface acoustic wave Brillouin scatering in thin-film lithium niobate waveguides
Optica Open. Preprint
David Marpaung is a full professor leading the Nonlinear Nanophotonics group at the University of Twente, the Netherlands. He is a fellow of Optica (formerly OSA). He was the recipient of the 2015 Discovery Early Career Research Award (DECRA) from the Australian Research Council, the 2017 Vidi award and the 2019 START UP grant from the Netherlands Organisation for Scientific Research (NWO). In 2022 he was awarded the ERC Consolidator grant on the topic of 3D photonic circuits for Brillouin scatering. His research interests include integrated photonics, nonlinear optics, and microwave photonics.
20.06.2024 Prof. Jörg Kröger
Vortragsankündigung
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27.06.2024 Prof. Christian Schneider
Vortragsankündigung
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04.07.2024 Verleihung des Lehrpreises / Prof. Beate Heinemann
Vortragsankündigung
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18.07.2024 Prof. Roman Engel-Herbert
Vortragsankündigung
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