42 research outputs found
Coherent multidimensional spectroscopy in the gas phase
Recent work applying multidimentional coherent electronic spectroscopy at
dilute samples in the gas phase is reviewed. The development of refined
phase-cycling approaches with improved sensitivity has opened-up new
opportunities to probe even dilute gas-phase samples. In this context, first
results of 2-dimensional spectroscopy performed at doped helium droplets reveal
the femtosecond dynamics upon electronic excitation of cold, weakly-bound
molecules, and even the induced dynamics from the interaction with the helium
environment. Such experiments, offering well-defined conditions at low
temperatures, are potentially enabling the isolation of fundamental processes
in the excitation and charge transfer dynamics of molecular structures which so
far have been masked in complex bulk environments.Comment: Invited Review Articl
Feldlerche - Alauda arvensis
Die Feldlerche gehört zur Reihe charakteristischer Vogelarten der offenen Feldflur, deren BestĂ€nde in jĂŒngster Zeit stark zurĂŒckgegangen sind. Das Heft bietet Art- und Lebensraum bezogene Informationen.
Redaktionsschluss: 03.07.201
Coherent multidimensional spectroscopy of dilute gas-phase nanosystems
Two-dimensional electronic spectroscopy (2DES) is one of the most powerful
spectroscopic techniques, capable of attaining a nearly complete picture of a
quantum system including its couplings, quantum coherence properties and its
real-time dynamics. While successfully applied to a variety of condensed phase
samples, high precision experiments on isolated quantum systems in the gas
phase have been so far precluded by insufficient sensitivity. However, such
experiments are essential for a precise understanding of fundamental mechanisms
and to avoid misinterpretations, e.g. as for the nature of quantum coherences
in energy trans-port. Here, we solve this issue by extending 2DES to isolated
nanosystems in the gas phase prepared by helium nanodroplet isolation in a
molecular beam-type experiment. This approach uniquely provides high
flexibility in synthesizing tailored, quantum state-selected model systems of
single and many-body properties. For demonstration, we deduce a precise and
conclusive picture of the ultrafast coherent dynamics in isolated high-spin Rb2
molecules and present for the first time a dynamics study of the system-bath
interaction between a single molecule (here Rb3) and a superfluid helium
environment. The results demonstrate the unique capacity to elucidate
prototypical interactions and dynamics in tailored quantum systems and bridges
the gap to experiments in ultracold quantum science
Worst case optimization for interfractional motion mitigation in carbon ion therapy of pancreatic cancer.
Introduction The efficacy of radiation therapy treatments for pancreatic cancer is compromised by abdominal motion which limits the spatial accuracy for dose delivery - especially for particles. In this work we investigate the potential of worst case optimization for interfractional offline motion mitigation in carbon ion treatments of pancreatic cancer.Methods We implement a worst case optimization algorithm that explicitly models the relative biological effectiveness of carbon ions during inverse planning. We perform a comparative treatment planning study for seven pancreatic cancer patients. Treatment plans that have been generated using worst case optimization are compared against (1) conventional intensity-modulated carbon ion therapy, (2) single field uniform dose carbon ion therapy, and (3) an ideal yet impractical scenario relying on daily re-planning. The dosimetric quality and robustness of the resulting treatment plans is evaluated using reconstructions of the daily delivered dose distributions on fractional control CTs.Results Idealized daily re-planning consistently gives the best dosimetric results with regard to both target coverage and organ at risk sparing. The absolute reduction of D 95 within the gross tumor volume during fractional dose reconstruction is most pronounced for conventional intensity-modulated carbon ion therapy. Single field uniform dose optimization exhibits no substantial reduction for six of seven patients and values for D 95 for worst case optimization fall in between. The treated volume (D>95 % prescription dose) outside of the gross tumor volume is reduced by a factor of two by worst case optimization compared to conventional optimization and single field uniform dose optimization. Single field uniform dose optimization comes at an increased radiation exposure of normal tissues, e.g. â2 Gy (RBE) in the mean dose in the kidneys compared to conventional and worst case optimization and â4 Gy (RBE) in D 1 in the spinal cord compared to worst case optimization.Conclusion Interfractional motion substantially deteriorates dose distributions for carbon ion treatments of pancreatic cancer patients. Single field uniform dose optimization mitigates the negative influence of motion on target coverage at an increased radiation exposure of normal tissue. Worst case optimization enables an exploration of the trade-off between robust target coverage and organ at risk sparing during inverse treatment planning beyond margin concepts
StraĂenbĂ€ume im lĂ€ndlichen Raum: Pflanzempfehlungen fĂŒr straĂenbegleitende Baumreihen und Alleen
Diese BroschĂŒre dient zur Information fĂŒr Kommunen, Planer, Baumfreunde und Interessierte. Sie gibt Anregungen, wie wieder mehr BĂ€ume an StraĂen im lĂ€ndlichen Raum gepflanzt werden können und was es dabei zu berĂŒcksichtigen gilt. Im Rahmen der gesetzlichen Anforderungen werden hierzu die aktuell gĂŒltigen Regelwerke sowie die unterschiedlichen fachlichen Sichtweisen und Herausforderungen dargestellt und beispielhafte Lösungsmöglichkeiten aufgezeigt.
Redaktionsschluss: 31.08.202
Observation of Antiferroelectric Domain Walls in a Uniaxial Hyperferroelectric
Ferroelectric domain walls are a rich source of emergent electronic
properties and unusual polar order. Recent studies showed that the
configuration of ferroelectric walls can go well beyond the conventional
Ising-type structure. N\'eel-, Bloch-, and vortex-like polar patterns have been
observed, displaying strong similarities with the spin textures at magnetic
domain walls. Here, we report the discovery of antiferroelectric domain walls
in the uniaxial ferroelectric PbGeO. We resolve highly
mobile domain walls with an alternating displacement of Pb atoms, resulting in
a cyclic 180 flip of dipole direction within the wall. Density
functional theory calculations reveal that PbGeO is
hyperferroelectric, allowing the system to overcome the depolarization fields
that usually suppress antiparallel ordering of dipoles along the longitudinal
direction. Interestingly, the antiferroelectric walls observed under the
electron beam are energetically more costly than basic head-to-head or
tail-to-tail walls. The results suggest a new type of excited domain-wall
state, expanding previous studies on ferroelectric domain walls into the realm
of antiferroic phenomena
Improved stabilization scheme for extreme ultraviolet quantum interference experiments
Interferometric pump-probe experiments in the extreme ultraviolet (XUV)
domain are experimentally very challenging due to the high phase stability
required between the XUV pulses. Recently, an efficient phase stabilization
scheme was introduced for seeded XUV free electron lasers (FELs) combining
shot-to-shot phase modulation with lock-in detection. This method stabilized
the seed laser beampath on the fundamental ultraviolet wavelength to a high
degree. Here, we extend this scheme including the stabilization of the XUV
beampath, incorporating phase fluctuations from the FEL high gain harmonic
generation process. Our analysis reveals a clear signal improvement with the
new method compared to the previous stabilization scheme
High-Gain Harmonic Generation with temporally overlapping seed pulses and application to ultrafast spectroscopy
Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG)
process in a free-electron laser (FEL) is a promising approach to facilitate
various coherent nonlinear spectroscopy schemes in the extreme ultraviolet
(XUV) spectral range. However, in collinear arrangements using a single
nonlinear medium, temporally overlapping seed pulses may introduce nonlinear
mixing signals that compromise the experiment at short time delays. Here, we
investigate these effects in detail by extending the analysis described in a
recent publication (Wituschek et al., Nat. Commun., 11, 883, 2020). High-order
fringe-resolved autocorrelation and wave-packet interferometry experiments at
photon energies > eV are performed, accompanied by numerical simulations.
It turns out that both the autocorrelation and the wave-packet interferometry
data are very sensitive to saturation effects and can thus be used to
characterize saturation in the HGHG process. Our results further imply that
time-resolved spectroscopy experiments are feasible even for time delays
smaller than the seed pulse duration.Comment: This is accepted version of the article. The Version of Record is
available online at https://doi.org/10.1364/OE.40124
Feldlerche - Alauda arvensis
Die Feldlerche gehört zur Reihe charakteristischer Vogelarten der offenen Feldflur, deren BestĂ€nde in jĂŒngster Zeit stark zurĂŒckgegangen sind. Das Heft bietet Art- und Lebensraum bezogene Informationen.
Redaktionsschluss: 03.07.201