Fakultät für Physik

Permanent URI for this collection

http://hdl.handle.net/2003/39779

Browse

Now showing 1 - 20 of 35

Measurements regarding a combined therapy concept for ophthalmic tumors consisting of brachytherapy and x-rays
(2024-06-26) Manke, Henning; Fluehs, D; Stroth, Michelle; Bechrakis, N E; Foerster, A M H; Albrecht, Johannes
Objective. We present a novel concept to treat ophthalmic tumors which combines brachytherapy and low-energy x-ray therapy. Brachytherapy with 106Ru applicators is inadequate for intraocular tumors with a height of 7 mm or more. This results from a steep dose gradient, and it is unfeasible to deliver the required dose at the tumor apex without exceeding the maximum tolerable sclera dose of usually 1000 Gy to 1500 Gy. Other modalities, such as irradiation with charged particles, may be individually contraindicated. A dose boost at the apex provided by a superficial x-ray therapy unit, performed simultaneously with the brachytherapy, results in a more homogeneous dose profile than brachytherapy alone. This avoids damage to organs at risk. The applicator may also serve as a beam stop for x-rays passing through the target volume, which reduces healthy tissue dosage. This study aims to investigate the suitability of the applicator to serve as a beam stop for the x-rays. Approach. A phantom with three detector types comprising a soft x-ray ionization chamber, radiochromic films, and a self-made scintillation detector was constructed to perform dosimetry. Measurements were performed using a conventional x-ray unit for superficial therapy to investigate the uncertainties of the phantom and the ability of the applicator to absorb x-rays. The manufacturer provided a dummy plaque to obtain x-ray dose profiles without noise from 106Ru decays. Results. The phantom is generally feasible to obtain dose profiles with three different detector types. The interaction of x-rays with the silver of the applicator leads to an increased dose rate in front of the applicator. The dose rate of the x-rays is reduced by up to 90% behind a 106Ru applicator. Therefore, a 106Ru applicator can be used as a beam stop in combined x-ray and brachytherapy treatment.
Structural, chemical, and magnetic investigation of a graphene/cobalt/platinum multilayer system on silicon carbide
(2024-02-21) Weinert, Philipp; Hochhaus, Julian; Kesper, Lukas; Appel, Robert; Hilgers, Stefanie; Schmitz, Marie; Schulte, Malte; Hönig, Richard; Kronast, Florian; Valencia, Sergio; Kruskopf, Mattias; Chatterjee, Atasi; Berges, Ulf; Westphal, Carsten
We investigate the magnetic interlayer coupling and domain structure of ultra-thin ferromagnetic (FM) cobalt (Co) layers embedded between a graphene (G) layer and a platinum (Pt) layer on a silicon carbide (SiC) substrate (G/Co/Pt on SiC). Experimentally, a combination of x-ray photoemission electron microscopy with x-ray magnetic circular dichroism has been carried out at the Co L-edge. Furthermore, structural and chemical properties of the system have been investigated using low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS). In situ LEED patterns revealed the crystalline structure of each layer within the system. Moreover, XPS confirmed the presence of quasi-freestanding graphene, the absence of cobalt silicide, and the appearance of two silicon carbide surface components due to Pt intercalation. Thus, the Pt-layer effectively functions as a diffusion barrier. The magnetic structure of the system was unaffected by the substrate’s step structure. Furthermore, numerous vortices and anti-vortices were found in all samples, distributed all over the surfaces, indicating Dzyaloshinskii–Moriya interaction. Only regions with a locally increased Co-layer thickness showed no vortices. Moreover, unlike in similar systems, the magnetization was predominantly in-plane, so no perpendicular magnetic anisotropy was found.
Fitting the DESI BAO data with dark energy driven by the Cohen-Kaplan-Nelson bound
(2024-08-28) Adolf, Patrick; Hirsch, Martin; Krieg, Sara; Päs, Heinrich; Tabet, Mustafa
Gravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet (UV) and infrared (IR) cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the IR cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a time-dependent dark energy density. In this paper we confront this idea with recent data from DESI BAO, Hubble and supernova measurements. We find that the CKN model provides a better fit to the data than the ΛCDM model and can compete with other models of time-dependent dark energy that have been studied so far.
Ultrafast optical induction of magnetic order at a quantum critical point
(2024-12-06) Fauseweh, Benedikt; Zhu, Jian-Xin
Time-resolved ultrafast spectroscopy has emerged as a promising tool to dynamically induce and manipulate non-trivial electronic states of matter out-of-equilibrium. Here we theoretically investigate light pulse driven dynamics in a Kondo lattice system close to quantum criticality. Based on a time-dependent auxiliary fermion mean-field calculation we show that light can dehybridize the local Kondo screening and induce oscillating magnetic order out of a previously paramagnetic state. Depending on the laser pulse field amplitude and frequency the Kondo singlet can be completely deconfined, inducing a dynamic Lifshitz transition that changes the Fermi surface topology. These phenomena can be identified in harmonic generation and time-resolved angle-resolved photoemission spectroscopy spectra. Our results shed new light on non-equilibrium states in heavy fermion systems.
Potential of neutrino telescopes to detect quantum gravity-induced decoherence in the presence of dark fermions
(2025-01-15) Domi, Alba; Eberl, Thomas; Hellmann, Dominik; Krieg, Sara; Päs, Heinrich
We assess the potential of neutrino telescopes to discover quantum-gravity-induced decoherence effects modeled in the open-quantum system framework and with arbitrary numbers of active and dark fermion generations, such as particle dark matter or sterile neutrinos. The expected damping of neutrino flavor oscillation probabilities as a function of energy and propagation length thus encodes information about quantum gravity effects and the fermion generation multiplicity in the dark sector. We employ a public Monte-Carlo dataset provided by the IceCube Collaboration to model the detector response and estimate the sensitivity of IceCube to oscillation effects in atmospheric neutrinos induced by the presented model. Our findings confirm the potential of very-large-volume neutrino telescopes to test this class of models and indicate higher sensitivities for increasing numbers of dark fermions.
Inter-subject cerebrovascular variability: a source of uncertainty for dose calculation to circulating blood cells for glioblastoma patients treated with modern radiotherapy techniques
(2024-08-21) Hammi, Abdelkhalek; Shusharina, Nadya; Djuffouo, Sonya
Purpose. To assess how inter-subject variations in brain vasculature among glioblastoma (GBM) patients affects the calculated dose received by circulating blood cells (CBC) during radiotherapy and its subsequent impact on CBC depletion. Methods. Ten GBM patients treated with either intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) were selected. For each patient, 23 cerebrovascular models were developed based on 23 healthy subject MR-angiography data to simulate intra- and inter-subject blood vessel diversity. Based on the corresponding treatment plan of the patient, the dose to CBC was calculated for all the 230 scenarios. The impact of inter-subject variation on fraction of irradiated blood volume (VD>0 cGy) and lymphocyte kill rates as a function of the clinical target volume (CTV) size and treatment technique were analyzed. Results. The dose fluctuation to CBC was higher in IMRT plans compared to VMAT plans. The uncertainty in the VD>0 cGy was 18.3% for IMRT and 2.0% (CI95%) for VMAT and the dispersion of the D2% index was 6 cGy for IMRT and 1 cGy for VMAT (CI95%) for one single treatment fraction of 200 cGy. The uncertainty in killed CBC due to inter-subject diversity in brain blood vessel increased with increasing CTV size and was σ = 11.2%. Conclusions. VMAT showed greater robustness against inter-subject variation in blood vessels compared to IMRT. We recommend considering the uncertainty in depleting CBC resulting from the use of less patient-specific and generic blood vessel phantoms to improve the radiation-induced lymphopenia assessments.
Relaxation and diffusion of an ionic plasticizer in amorphous poly(vinylpyrrolidone)
(2024-04-18) Röwekamp, Lara; Moch, Kevin; Seren, Merve; Münzner, Philipp; Böhmer, Roland; Gainaru, Catalin
The present work focuses on the dynamics of the ionic constituents of 1-propyl-3-methyl-imidazolium-bis-(trifluormethylsulfonyl)-imide (PT), a paradigmatic ionic liquid, as an additive in poly(vinylpyrrolidone) (PVP). Hence, the resulting product can be regarded as a polymer electrolyte as well as an amorphous dispersion. Leveraging dielectric spectroscopy and oscillatory shear rheology, complemented by differential scanning calorimetry, the spectral shapes and the relaxation maps of the supercooled PVP-PT mixtures are accessed in their full compositional range. The study also presents dielectric and shear responses of neat PVP with a molecular weight of 2500 g mol−1. We discuss the plasticizing role of the PT additive and the decoupling between ionic dynamics and segmental relaxation in these mixtures. The extracted relaxation times, steady-state viscosities, and conductivities are employed to estimate the translational diffusivities of the ionic penetrants by means of the Stokes–Einstein, Nernst–Einstein, and Almond–West relations. While some of the estimated diffusivities agree with each other, some do not, pointing to the importance of the chosen hydrodynamic approximations and the type of response considered for the analysis. The present extensive dielectric, rheological, and calorimetric study enables a deeper understanding of relaxation and transport of ionic ingredients in polymers, particularly in the slow-dynamics regime which is difficult to access experimentally by direct-diffusivity probes.
Effect of crystal symmetry of lead halide perovskites on the optical orientation of excitons
(2025-02-20) Kopteva, Nataliia E.; Yakovlev, Dmitri R.; Yalcin, Eyüp; Kalitukha, Ina V.; Akimov, Ilya A.; Nestoklon, Mikhail O.; Turedi, Bekir; Hordiichuk, Oleh; Dirin, Dmitry N.; Kovalenko, Maksym V.; Bayer, Manfred
The great variety of lead halide perovskite semiconductors represents an outstanding platform for studying crystal symmetry effects on the spin-dependent properties. Access to them is granted through the optical orientation of exciton and carrier spins by circularly polarized photons. Here, the exciton spin polarization is investigated at 1.6 K cryogenic temperature in four lead halide perovskite crystals with different symmetries: (almost) cubic in FA0.9Cs0.1PbI2.8Br0.2 and FAPbBr3, and orthorhombic in MAPbI3 and CsPbBr3. Giant optical orientation of 85% is found for the excitons in FA0.9Cs0.1PbI2.8Br0.2, MAPbI3, and CsPbBr3, while it amounts to 20% in FAPbBr3. For all studied crystals, the optical orientation is robust to detuning of the laser photon energy from the exciton resonance, remaining constant for high energy detunings up to 0.3 eV, above which it continuously decreases to zero for detunings exceeding 1 eV. No acceleration of the spin relaxation for excitons with large kinetic energy is found in the cubic and orthorhombic crystals. This evidences the absence of the Dyakonov-Perel spin relaxation mechanism, which is based on the Rashba-Dresselhaus splitting of spin states at finite k-vectors. This indicates that the spatial inversion symmetry is maintained in perovskite crystals, independent of the cubic or orthorhombic phase.
Exploring nonlinear dynamics in periodically driven time crystal from synchronization to chaotic motion
(2025-03-26) Greilich, Alex; Kopteva, Nataliia E.; Korenev, Vladimir L.; Haude, Philipp A.; Bayer, Manfred
The coupled electron-nuclear spin system in an InGaAs semiconductor as testbed of nonlinear dynamics can develop auto-oscillations, resembling time-crystalline behavior, when continuously excited by a circularly polarized laser. We expose this system to deviations from continuous driving by periodic modulation of the excitation polarization, revealing a plethora of nonlinear phenomena that depend on modulation frequency and depth. We find ranges in which the system’s oscillations are entrained with the modulation frequency. The width of these ranges depends on the polarization modulation depth, resulting in an Arnold tongue pattern. Outside the tongue, the system shows a variety of fractional subharmonic responses connected through bifurcation jets when varying the modulation frequency. Here, each branch in the frequency spectrum forms a devil’s staircase. When an entrainment range is approached by going through an increasing order of bifurcations, chaotic behavior emerges. These findings can be described by an advanced model of the periodically pumped electron-nuclear spin system. We discuss the connection of the obtained results to different phases of time matter.
Time-resolved momentum microscopy with fs-XUV photons at high repetition rates with flexible energy and time resolution
(2025-01-29) Schiller, Karl Jakob; Sternemann, Lasse; Stupar, Matija; Omar, Alan; Hoffmann, Martin; Nitschke, Jonah Elias; Mischke, Valentin; Janas, David Maximilian; Ponzoni, Stefano; Zamborlini, Giovanni; Saraceno, Clara Jody; Cinchetti, Mirko
Time-resolved momentum microscopy is an emerging technique based on photoelectron spectroscopy for characterizing ultrafast electron dynamics and the out-of-equilibrium electronic structure of materials in the entire Brillouin zone with high efficiency. In this article, we introduce a setup for time-resolved momentum microscopy based on an energy-filtered momentum microscope coupled to a custom-made high-harmonic generation photon source driven by a multi-100 kHz commercial Yb-ultrafast laser that delivers fs pulses in the extreme ultraviolet range. The laser setup includes a nonlinear pulse compression stage employing spectral broadening in a Herriott-type bulk-based multi-pass cell. This element allows flexible tuning of the driving pulse duration, providing a versatile time-resolved momentum microscopy setup featuring two operational modes designed to enhance either the energy or time resolution. We show the capabilities of the system by tracing ultrafast electron dynamics in the conduction band valleys of a bulk crystal of the 2D semiconductor WS2. Using uncompressed driving laser pulses, we demonstrate an energy resolution better than (107 ± 2) meV, while compressed pulses lead to a time resolution better than (48.8 ± 17) fs.
Structural analysis of Sn on Au(111) at low coverages: towards the Au2Sn surface alloy with alternating fcc and hcp domains
(2025-03-07) Hochhaus, Julian Andreas; Hilgers, Stefanie; Schmitz, Marie; Kesper, Lukas; Berges, Ulf; Westphal, Carsten
We report on the structural and chemical evolution of submonolayer Sn on Au(111) up to the formation of the striped Au2Sn surface alloy. Using Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM), we identify a previously unobserved hexagonal (2 × 2) -reconstruction at a Sn film thickness of ˜ 0.28 monolayers (ML). X-ray Photoelectron Spectroscopy (XPS) analysis reveals that the (2 × 2)-structure is not chemically bonded to the Au(111) substrate. With increasing Sn coverage, the (2 × 2)-reconstruction performs a structural transition into a mixed phase before forming a local (v3 × v3)R30.-reconstruction at a Sn film thickness of 0.33ML. This reconstruction is superimposed by a larger periodicity resembling the herringbone reconstruction of clean Au(111). Our XPS analysis identifies this phase as an Au2Sn-alloy. By combining high-resolution x-ray photoelectron diffraction (XPD) measurements of Au 4f and Sn 4d 4d core levels with simulations based on a genetic algorithm, we propose a structural model for the Au2Sn-supercell, revealing an unusually large unit cell with Rec(26 × v3)-periodicity. This study advances the understanding of the structural evolution of Sn surface reconstructions on Au(111) up to the formation of the Au2Sn surface alloy. Furthermore, it provides insights into the structural arrangements emerging at higher submonolayer Sn coverages on Au(111), offering potential pathways towards realizing freestanding stanene.
Ultrafast unidirectional spin Hall magnetoresistance driven by terahertz light field
(2025-03-06) Salikhov, Ruslan; IIlyakov, Igor; Reinold, Anneke; Deinert, Jan-Christoph; Oliveira, Thales V. A. G. de; Ponomaryov, Alexey; Prajapati, Gulloo Lal; Pilch, Patrick; Ghalgaoui, Ahmed; Koch, Max; Fassbender, Jürgen; Lindner, Jürgen; Whang, Zhe; Kovalev, Sergey
The ultrafast control of magnetisation states in magnetically ordered systems poses significant technological challenges yet is vital for the development of memory devices that operate at picosecond timescales or terahertz (THz) frequencies. Despite considerable efforts achieving convenient ultrafast readout of magnetic states remains an area of active investigation. For practical applications, energy-efficient and cost-effective electrical detection is highly desirable. In this context, unidirectional spin-Hall magnetoresistance (USMR) has been proposed as a straightforward two-terminal geometry for the electrical detection of magnetisation states in magnetic heterostructures. In this work, we demonstrate that USMR is effective at THz frequencies, enabling picosecond time readouts initiated by light fields. We observe ultrafast USMR in various ferromagnet/heavy metal thin film heterostructures via THz second-harmonic generation. Our findings, along with temperature-dependent measurements of USMR, reveal a substantial contribution from electron-magnon spin-flip scattering, highlighting the potential for all-electrical detection of THz magnon modes.
Theory and applications of wide field surface plasmon resonance microscopy for discrete particles detection
(2025) Al Bataineh, Qais Mohammed Turki; Franzke, Joachim; Bayer, Manfred
Detecting and characterizing nano-objects with low concentrations, such as biological particles, is a substantial challenge in analytical science. The wide-field surface plasmon resonance microscopy (WF-SPRM) can detect individual nano-objects in solutions and gas media bound to the sensor surface. Therefore, WF-SPRM can detect low nano-object concentrations because the image contains several square millimeters. In this work, the fundamental parameters for building highly sensitive WF-SPRM were optimized. WF-SPRM can detect individual nano-objects in solutions and gas media. Therefore, we derived a discrete particle model of SPR to describe the SPR sensor of discrete particle detection. Theoretical, numerical, and experimental analyses of the SPR detection principle were performed by considering discrete particle detection. Additionally, the influence on the SPR sensitivity of coating the gold/silver layer with a dielectric layer with varying refractive index is also studied. Different polyelectrolyte brushes, like polyacrylic acid, polyacrylic acid-polyethylene oxide, and polyacrylic acid/iodine, are used to validate the enhancement of the SPR sensitivity. Validation experiments are performed using polystyrene and silica nanoparticles of varying sizes. Finally, the surface plasmon coupling behavior between the localized surface plasmons (LSPs) of different shapes and sizes of metal nanostructures and the propagating surface plasmons (PSPs) of the metal surface is investigated by employing experimental, simulation, and theoretical approaches.
Mit B-Mesonen auf der Suche nach neuer Physik
(2023-05-02) Seuthe, Alex; Albrecht, Johannes
Zurzeit ist die Flavour-Physik mit der Untersuchung von Zerfällen von B-Mesonen ein interessanter Bereich der experimentellen Teilchenphysik, da sie wichtige Tests des Standardmodells ermöglicht. Das kürzlich überarbeitete LHCb-Experiment wurde neu gestartet und soll eine bisher unerreichte Präzision in der Vermessung der Eigenschaften der B-Mesonen liefern.
SMARTINI3 parametrization of multi-scale membrane models via unsupervised learning methods
(2024-10-28) Risselada, Herre Jelger; Soleimani, Alireza
In this study, we utilize genetic algorithms to develop a realistic implicit solvent ultra-coarse-grained (ultra-CG) membrane model comprising only three interaction sites. The key philosophy of the ultra-CG membrane model SMARTINI3 is its compatibility with realistic membrane proteins, for example, modeled within the Martini coarse-grained (CG) model, as well as with the widely used GROMACS software for molecular simulations. Our objective is to parameterize this ultra-CG model to accurately reproduce the experimentally observed structural and thermodynamic properties of Phosphatidylcholine (PC) membranes in real units, including properties such as area per lipid, area compressibility, bending modulus, line tension, phase transition temperature, density profile, and radial distribution function. In our example, we specifically focus on the properties of a POPC membrane, although the developed membrane model could be perceived as a generic model of lipid membranes. To optimize the performance of the model (the fitness), we conduct a series of evolutionary runs with diverse random initial population sizes (ranging from 96 to 384). We demonstrate that the ultra-CG membrane model we developed exhibits authentic lipid membrane behaviors, including self-assembly into bilayers, vesicle formation, membrane fusion, and gel phase formation. Moreover, we demonstrate compatibility with the Martini coarse-grained model by successfully reproducing the behavior of a transmembrane domain embedded within a lipid bilayer. This facilitates the simulation of realistic membrane proteins within an ultra-CG bilayer membrane, enhancing the accuracy and applicability of our model in biophysical studies.
Few-photon SUPER: quantum emitter inversion via two off-resonant photon modes
(2025-01-21) Richter, Quentin W.; Kaspari, Jan M.; Bracht, Thomas K.; Yatsenko, Leonid; Axt, Vollrath Martin; Rauschenbeutel, Arno; Reiter, Doris E.
With the realization of controlled quantum systems, exploring excitations beyond the resonant case opens new possibilities. We investigate an extended Jaynes-Cummings model in which two nondegenerate photon modes are coupled off resonantly to a quantum emitter. This allows us to identify few-photon scattering mechanisms that lead to a full inversion of the emitter while transferring off-resonant photons from one mode to another. This behavior is connected to recent measurements of a two-level emitter scattering two off-resonant photons simultaneously. Furthermore, our results can be understood as a quantized analog of the recently developed off-resonant quantum control scheme known as swing-up of quantum emitter (SUPER). Our intuitive formalism gives deeper insight into the interaction of a two-level emitter with off-resonant light modes with the prospect of novel photonic applications.
Wide-field surface plasmon resonance microscope based on polyethylene oxide/polyacrylic acid brushes
(2023-12-21) Al-Bataineh, Qais M.; Hergenröder, Roland; Telfah, Ahmad D.; Tavares, Carlos J.
Wide-ﬁeld surface plasmon resonance microscope (WF-SPRM) based on polyethylene oxide/polyacrylic acid (PEO/PAA) polyelectrolyte brushes (PEBs) is presented for particle detection application. PEO acts as an H-bond acceptor, while PAA serves as an H-bond donor, forming hydrogen-bonding complexes within the brushes. Morphological, chemical, and crystal structural analyses conﬁrm that the PEO/PAA brushes undergo a transition from a collapsed to a stretched state as the solvent pH is increased from 1 to 10. This pH-dependent change also renders the PEO/PAA brushes more hydrophilic. Additionally, the electrical conductivity and refractive index of the PEO/PAA brushes increase concomitantly with the increase of solvent pH. Furthermore, theoretical and experimental approaches study the sensitivity of WF-SPRM utilizing Au-(PEO/PAA) polyelectrolyte layers. The theoretical sensitivity of WF-SPRM is enhanced from 118.5 deg./RIU for the Au-layer to 178.1 deg./RIU for Au- (PEO/PAA PEBs). Moreover, the signal-to-noise ratio for the Au-(PEO/PAA PEBs) layer is 20 ± 1, indicating improved sensing performance compared to the Au-layer (signal-to-noise ratio of 6 ± 1). A mathematical model to describe the discrete particle detection by WF-SPRM is presented, where results demonstrate a good agreement between the calculated intensity proﬁle and experimental data.
The dirty and clean dose concept: towards creating proton therapy treatment plans with a photon-like dose response
(2023-10-25) Heuchel, Lena; Hahn, Christian; Ödén, Jakob; Traneus, Erik; Wulff, Jörg; Timmermann, Beate; Bäumer, Christian; Lühr, Armin
Background: Applying tolerance doses for organs at risk (OAR) from photon therapy introduces uncertainties in proton therapy when assuming a constant relative biological effectiveness (RBE) of 1.1. Purpose: This work introduces the novel dirty and clean dose concept, which allows for creating treatment plans with a more photon-like dose response for OAR and, thus, less uncertainties when applying photon-based tolerance doses. Methods: The concept divides the 1.1-weighted dose distribution into two parts: the clean and the dirty dose. The clean and dirty dose are deposited by protons with a linear energy transfer (LET) below and above a set LET threshold, respectively. For the former, a photon-like dose response is assumed, while for the latter, the RBE might exceed 1.1. To reduce the dirty dose in OAR, a MaxDirtyDose objective was added in treatment plan optimization. It requires setting two parameters: LET threshold and max dirty dose level. A simple geometry consisting of one target volume and one OAR in water was used to study the reduction in dirty dose in the OAR depending on the choice of the two MaxDirtyDose objective parameters during plan optimization. The best performing parameter combinations were used to create multiple dirty dose optimized (DDopt) treatment plans for two cranial patient cases. For each DDopt plan, 1.1-weighted dose, variable RBE-weighted dose using the Wedenberg RBE model and dose-average LETd distributions as well as resulting normal tissue complication probability (NTCP) values were calculated and compared to the reference plan (RefPlan) without MaxDirtyDose objectives. Results: In the water phantom studies, LET thresholds between 1.5 and 2.5 keV/µm yielded the best plans and were subsequently used. For the patient cases, nearly all DDopt plans led to a reduced Wedenberg dose in critical OAR. This reduction resulted from an LET reduction and translated into an NTCP reduction of up to 19 percentage points compared to the RefPlan. The 1.1-weighted dose in the OARs was slightly increased (patient 1: 0.45 Gy(RBE), patient 2: 0.08 Gy(RBE)), but never exceeded clinical tolerance doses. Additionally, slightly increased 1.1-weighted dose in healthy brain tissue was observed (patient 1: 0.81 Gy(RBE), patient 2: 0.53 Gy(RBE)). The variation of NTCP values due to variation of α/β from 2 to 3 Gy was much smaller for DDopt (2 percentage points (pp)) than for RefPlans (5 pp). Conclusions: The novel dirty and clean dose concept allows for creating biologically more robust proton treatment plans with a more photon-like dose response. The reduced uncertainties in RBE can, therefore, mitigate uncertainties introduced by using photon-based tolerance doses for OAR.
Mode-multiplexing deep-strong light-matter coupling
(2024-02-28) Mornhinweg, Joshua; Diebel, Laura Katharina; Halbhuber, Maike; Prager, Michael; Riepl, Josef; Inzenhofer, Tobias; Bougeard, Dominique; Huber, Rupert; Lange, Christoph
Dressing electronic quantumstates with virtual photons creates exotic effects ranging from vacuum-field modified transport to polaritonic chemistry, and squeezing or entanglement of modes. The established paradigm of cavity quantum electrodynamics maximizes the light-matter coupling strength ΩR=ωc, defined as the ratio of the vacuumRabi frequency and the frequency of light, by resonant interactions. Yet, the finite oscillator strength of a single electronic excitation sets a natural limit to ΩR=ωc. Here, we enter a regime of record-strong light-matter interaction which exploits the cooperative dipole moments of multiple, highly non-resonant magnetoplasmon modes tailored by ourmetasurface. This creates an ultrabroadband spectrum of 20 polaritons spanning 6 optical octaves, calculated vacuum ground state populations exceeding 1 virtual excitation quantum, and coupling strengths equivalent to ΩR=ωc =3:19. The extreme interaction drives strongly subcycle energy exchange between multiple bosonic vacuum modes akin to high-order nonlinearities, and entangles previously orthogonal electronic excitations solely via vacuum fluctuations.
Unveiling the interplay of Mollow physics and perturbed free induction decay by nonlinear optical signals of a dynamically driven two-level system
(2024-05-13) Kaspari, Jan M.; Bracht, Thomas K.; Boos, Katarina; Kim, Sang Kyu; Sbresny, Friedrich; Müller, Kai; Reiter, Doris E.
Nonlinear optical signals in optically driven quantum systems can reveal coherences and thereby open up the possibility for manipulation of quantum states. While the limiting cases of ultrafast and continuous-wave excitation have been extensively studied, the time dynamics of finite pulses bear interesting phenomena. In this paper, we explore the nonlinear optical probe signals of a two-level system excited with a laser pulse of finite duration. In addition to the prominent Mollow peaks, the probe spectra feature several smaller peaks for certain time delays. Similar features have been recently observed for resonance fluorescence signals [K. Boos et al., Phys. Rev. Lett. 132, 053602 (2024)]. We discuss that the emergent phenomena can be explained by a combination of Mollow triplet physics and perturbed free induction decay effects, providing an insightful understanding of the underlying physics.

Browse

Recent Submissions