42 research outputs found
Multi-dimensional laser spectroscopy of exciton-polaritons with spatial light modulators
We describe an experimental system that allows one to easily access the
dispersion curve of exciton-polaritons in a microcavity. Our approach is based
on two spatial light modulators (SLM), one for changing the excitation angles
(momenta), and the other for tuning the excitation wavelength. We show that
with this setup, an arbitrary number of states can be excited accurately and
that re-configuration of the excitation scheme can be done at high speed.Comment: 4 pages, 5 figure
Effects of Caffeine on the Muscular Endurance, Perceived Pain, and Effort of Resistance Trained Women
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Uncovering dispersion properties in semiconductor waveguides to study photon-pair generation
This work was supported by the FWF through project no. I-2065-N27, the DFG Project no. SCHN1376/2-1, the ERC project EnSeNa (257531) and the State of Bavaria.We investigate the dispersion properties of ridge Bragg-reflection waveguides to deduce their phasematching characteristics. These are crucial for exploiting them as sources of parametric down-conversion (PDC). In order to estimate the phasematching bandwidth we first determine the group refractive indices of the interacting modes via Fabry–Perot experiments in two distant wavelength regions. Second, by measuring the spectra of the emitted PDC photons, we gain access to their group index dispersion. Our results offer a simple approach for determining the PDC process parameters in the spectral domain, and provide important feedback for designing such sources, especially in the broadband case.Publisher PDFPeer reviewe
Semi-automatic engineering and tailoring of high-efficiency Bragg-reflection waveguide samples for quantum photonic applications
Austrian Science Fund (FWF) (I-2065, J-4125); German Research Foundation (DFG) (SCHN1376/2-1); European Research Council (ERC) (EnSeNa 257531); State of Bavaria; China Scholarship Council (201503170272)Semiconductor alloys of aluminum gallium arsenide (AlGaAs) exhibit strong second-order optical nonlinearities. This makes them prime candidates for the integration of devices for classical nonlinear optical frequency conversion or photon-pair production, for example, through the parametric down-conversion (PDC) process. Within this material system, Bragg-reflection waveguides (BRW) are a promising platform, but the specifics of the fabrication process and the peculiar optical properties of the alloys require careful engineering. Previously, BRW samples have been mostly derived analytically from design equations using a fixed set of aluminum concentrations. This approach limits the variety and flexibility of the device design. Here, we present a comprehensive guide to the design and analysis of advanced BRW samples and show how to automatize these tasks. Then, nonlinear optimization techniques are employed to tailor the BRW epitaxial structure towards a specific design goal. As a demonstration of our approach, we search for the optimal effective nonlinearity and mode overlap which indicate an improved conversion efficiency or PDC pair production rate. However, the methodology itself is much more versatile as any parameter related to the optical properties of the waveguide, for example the phasematching wavelength or modal dispersion, may be incorporated as design goals. Further, we use the developed tools to gain a reliable insight in the fabrication tolerances and challenges of real-world sample imperfections. One such example is the common thickness gradient along the wafer, which strongly influences the photon-pair rate and spectral properties of the PDC process. Detailed models and a better understanding of the optical properties of a realistic BRW structure are not only useful for investigating current samples, but also provide important feedback for the design and fabrication of potential future turn-key devices. This approach limits the variety and exibility of the device design. Here, we present a comprehensive guide to the design and analysis of advanced BRW samples and show how to automatize these tasks. Then, nonlinear optimization techniques are employed to tailor the BRW epitaxial structure towards a specific design goal. As a demonstration of our approach, we search for the optimal effective nonlinearity and mode overlap which indicate an improved conversion effciency or PDC pair production rate. However, the methodology itself is much more versatile as any parameter related to the optical properties of the waveguide, for example the phasematching wavelength or modal dispersion, may be incorporated as design goals. Further, we use the developed tools to gain a reliable insight in the fabrication tolerances and challenges of real-world sample imperfections. One such example is the common thickness gradient along the wafer, which strongly influences the photon-pair rate and spectral properties of the PDC process. Detailed models and a better understanding of the optical properties of a realistic BRW structure are not only useful for investigating current samples, but also provide important feedback for the design and fabrication of potential future turn-key devices.PostprintPeer reviewe
A comprehensive sensitivity and uncertainty analysis for discharge and nitrate-nitrogen loads involving multiple discrete model inputs under future changing conditions
Environmental modeling studies aim to infer the impacts on environmental
variables that are caused by natural and human-induced changes in
environmental systems. Changes in environmental systems are typically
implemented as discrete scenarios in environmental models to simulate
environmental variables under changing conditions. The scenario development
of a model input usually involves several data sources and perhaps other
models, which are potential sources of uncertainty. The setup and the
parametrization of the implemented environmental model are additional sources
of uncertainty for the simulation of environmental variables. Yet to draw
well-informed conclusions from the model simulations it is essential to
identify the dominant sources of uncertainty.
In impact studies in two Austrian catchments the eco-hydrological model Soil
and Water Assessment Tool (SWAT) was applied to simulate discharge and
nitrate-nitrogen (NO3--N) loads under future changing
conditions. For both catchments the SWAT model was set up with different
spatial aggregations. Non-unique model parameter sets were identified that
adequately reproduced observations of discharge and NO3--N
loads. We developed scenarios of future changes for land use, point source
emissions, and climate and implemented the scenario realizations in the
different SWAT model setups with different model parametrizations, which
resulted in 7000Â combinations of scenarios and model setups for both
catchments. With all model combinations we simulated daily discharge and
NO3--N loads at the catchment outlets.
The analysis of the 7000Â generated model combinations of both case studies
had two main goals: (i)Â to identify the dominant controls on the simulation
of discharge and NO3--N loads in the two case studies and
(ii)Â to assess how the considered inputs control the simulation of discharge
and NO3--N loads. To assess the impact of the input scenarios,
the model setup, and the parametrization on the simulation of discharge and
NO3--N loads, we employed methods of global sensitivity
analysis (GSA). The uncertainties in the simulation of discharge and
NO3--N loads that resulted from the 7000Â SWAT model combinations
were evaluated visually. We present approaches for the visualization of the
simulation uncertainties that support the diagnosis of how the analyzed
inputs affected the simulation of discharge and NO3--N loads.
Based on the GSA we identified climate change and the model parametrization
as being the most influential model inputs for the simulation of discharge and
NO3--N loads in both case studies. In contrast, the impact of
the model setup on the simulation of discharge and NO3--N loads
was low, and the changes in land use and point source emissions were found to
have the lowest impact on the simulated discharge and NO3--N
loads. The visual analysis of the uncertainty bands illustrated that the
deviations in precipitation of the different climate scenarios to historic
records dominated the changes in simulation outputs, while the differences in
air temperature showed no considerable impact.</p
Temporally versatile polarization entanglement from Bragg reflection waveguides
This work was supported by the FWF through project no. I-2065-N27, the DFG Project no. SCHN1376/2-1, the ERC project EnSeNa (257531) and the State of Bavaria.Bragg reflection waveguides emitting broadband parametric downconversion (PDC) have been proven to be well suited for the on-chip generation of polarization entanglement in a straightforward fashion [Sci. Rep. 3, 2314 (2013)]. Here, we investigate how the properties of the created states can be modified by controlling the relative temporal delay between the pair of photons created via PDC. Our results offer an easily accessible approach for changing the coherence of the polarization entanglement, in other words, to tune the phase of the off-diagonal elements of the density matrix. Furthermore, we provide valuable insight into the engineering of these states directly at the source.PostprintPeer reviewe
Optimizing the spectro-temporal properties of photon pairs from Bragg-reflection waveguides
This work was supported by the Austrian Science Fund (FWF) through the project nos. I-2065-N27 and J-4125-N27, the DFG project no. SCHN1376/2-1, the ERC project EnSeNa (257531), the State of Bavaria, China Scholarship Council project no. 201503170272, and Natural Science Foundation of Hunan Province of China project no. 2018JJ2467.Bragg-reflection waveguides (BRWs) fabricated from AlGaAs provide an interesting non-linear optical platform for photon-pair generation via parametric down-conversion (PDC). In contrast to many conventional PDC sources, BRWs are made of high refractive index materials and their characteristics are very sensitive to the underlying layer structure. First, we show that the design parameters like the phasematching wavelength and the group refractive indices of the interacting modes can be reliably controlled even in the presence of fabrication tolerances. We then investigate, how these characteristics can be taken advantage of when designing quantum photonic applications with BRWs. We especially concentrate on achieving a small differential group delay between the generated photons of a pair and then explore the performance of our design when realizing a Hong-Ou-Mandel interference experiment or generating spectrally multi-band polarization entangled states. Our results show that the versatility provided by engineering the dispersion in BRWs is important for employing them in different quantum optics tasks.Publisher PDFPeer reviewe
Carrier relaxation, pseudogap, and superconducting gap in high-Tc cuprates: A Raman scattering study
We describe results of electronic Raman-scattering experiments in differently
doped single crystals of Y-123 and Bi-2212. The comparison of AF insulating and
metallic samples suggests that at least the low-energy part of the spectra
originates predominantly from excitations of free carriers. We therefore
propose an analysis of the data in terms of a memory function approach.
Dynamical scattering rates and mass-enhancement factors for the carriers are
obtained. In B2g symmetry the Raman data compare well to the results obtained
from ordinary and optical transport. For underdoped materials the dc scattering
rates in B1g symmetry become temperature independent and considerably larger
than in B2g symmetry. This increasing anisotropy is accompanied by a loss of
spectral weight in B2g symmetry in the range between the superconducting
transition at Tc and a characteristic temperature T* of order room temperature
which compares well with the pseudogap temperature found in other experiments.
The energy range affected by the pseudogap is doping and temperature
independent. The integrated spectral loss is approximately 25% in underdoped
samples and becomes much weaker towards higher carrier concentration. In
underdoped samples, superconductivity related features in the spectra can be
observed only in B2g symmetry. The peak frequencies scale with Tc. We do not
find a direct relation between the pseudogap and the superconducting gap.Comment: RevTeX, 21 pages, 24 gif figures. For PostScript with embedded eps
figures, see http://www.wmi.badw-muenchen.de/~opel/k2.htm