A5012599276- Cold Atom Physics and Bose-Einstein Condensates
- Quantum Mechanics and Applications
- Terahertz technology and applications
- Acoustic Wave Resonator Technologies
- Superconducting and THz Device Technology
- ZnO doping and properties
- Quantum Information and Cryptography
- GaN-based semiconductor devices and materials
- Ga2O3 and related materials
- Advanced Frequency and Time Standards
- Atomic and Subatomic Physics Research
- Microwave Engineering and Waveguides
- Photonic and Optical Devices
- Microwave and Dielectric Measurement Techniques
- Semiconductor Quantum Structures and Devices
- Antenna Design and Analysis
- Gas Sensing Nanomaterials and Sensors
- Semiconductor materials and devices
- Dental Implant Techniques and Outcomes
- Gyrotron and Vacuum Electronics Research
- Opportunistic and Delay-Tolerant Networks
- Surface Modification and Superhydrophobicity
- Quantum and Classical Electrodynamics
- Electronic and Structural Properties of Oxides
- Antenna Design and Optimization
Laser- und Medizin-Technologie (Germany)
2012-2024
Leibniz University Hannover
2015-2021
Otto-von-Guericke University Magdeburg
2013-2020
Universität der Bundeswehr München
1979
Munich University of Applied Sciences
1963-1967
The interplay between band gap renormalization and filling (Burstein-Moss effect) in n-type wurtzite GaN is investigated. For a wide range of electron concentrations up to $1.6\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ spectroscopic ellipsometry photoluminescence were used determine the dependence energy Fermi edge on density. dominating effect an density about...
Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and realize second. In a classical interferometer, an ensemble atoms is prepared one two input states, whereas second left empty. this case, vacuum noise restricts interferometer standard quantum limit (SQL). Here, we propose experimentally demonstrate novel clock configuration that surpasses SQL by squeezing empty state. We create squeezed state containing average...
Abstract In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of quantum mechanics by devising a state two massive particles with maximally correlated space momentum coordinates. The EPR criterion qualifies such continuous-variable entangled states, where measurement one subsystem seemingly allows for prediction second beyond Heisenberg uncertainty relation. Up to now, correlations have only been created photons, while demonstration strongly states is still outstanding....
Modern quantum technologies in the fields of computing, simulation and metrology require creation control large ensembles entangled particles. In ultracold neutral atoms, highly states containing thousands particles have been generated, outnumbering any other physical system by orders magnitude. The entanglement generation relies on fundamental particle-exchange symmetry identical particles, which lacks standard notion between clearly definable subsystems. Here we present two spatially...
Compared to light interferometers, the flux in cold-atom interferometers is low and associated shot noise large. Sensitivities beyond these limitations require preparation of entangled atoms different momentum modes. Here, we demonstrate a source that compatible with state-of-the-art interferometers. Entanglement transferred from spin degree freedom Bose-Einstein condensate well-separated modes, witnessed by squeezing parameter -3.1(8) dB. Entanglement-enhanced atom promise unprecedented...
The waveguide of the general cross section is transformed into a rectangular by conformal transformation. electric and magnetic field, critical frequency, wall current, power transport attenuation different TE-and TM-modes are calculated series approximation. Examples numerical evaluation given for five sections.
Several novel types of detectors for the measurement electromagnetic radiation in THz spectral range are described. Firstly, based on pyroelectric foil coated with different absorbers have been developed focusing following features: high accuracy due to well-characterized absorption, sensitivity, large area and frequency polarization independence. A three-dimensional design five absorptions gave an overall absorption more than 98 %. Secondly, foils thin metal layers were realized. An 50 %...
The anisotropic effective electron masses in wurtzite GaN are determined by generalized infrared spectroscopic ellipsometry. Nonpolar (112¯0) oriented thin films allow accessing both masses, m⊥* and m∥*, determining the screened plasma frequencies. A n-type doping range up to 1.7 × 1020 cm−3 is investigated. mass ratio m⊥*/m∥* obtained with highest accuracy found be 1.11 independent on concentration 1.2 cm−3. For higher concentrations, conduction band non-parabolicity mirrored changes....
Abstract Generalized infrared spectroscopic ellipsometry (GIRSE) was applied to Sb‐doped rutile SnO 2 (101) films grown by plasma‐assisted molecular beam epitaxy (PAMBE). Coupled longitudinal‐optical (LO) phonon–plasmon (LPP) modes for the two principal polarization directions of optically anisotropic were identified and their frequencies determined as a function electron concentrations obtained Hall effect measurements. The analysis these yielded very accurate values plasma finally...
Spectroscopic ellipsometry at room temperature is applied in order to determine the ordinary (ε⊥) and extraordinary (ε∥) dielectric functions (DFs) of rutile SnO2 corresponding electric field (E) polarization perpendicular (E⊥c) parallel (E∥c) optical axis (c), respectively. Strong anisotropic behavior found for full spectral range from 0.5 up 20 eV. The onsets strong absorption are 4.28 eV 5.42 E⊥c E∥c, A dipole-forbidden band gap (3.59 ± 0.2) by line shape fits imaginary parts DFs. Further...
Nonpolar n-type doped a-plane GaN films were grown by metal-organic vapor phase epitaxy on r-plane sapphire substrates using silane and isobutylgermane as Si Ge dopants, respectively. It is found that Ge-doping acts a surfactant enabling the growth of fully coalesced mirror-like with electron concentrations above 1020 cm−3. Si-doping in excess 2×1019 cm−3 shows an antisurfactant behavior leading to surface degradation. No significant impact strain was for any dopant. Results ordinary...
In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of quantum mechanics by devising a state two massive particles with maximally correlated space momentum coordinates. The EPR criterion qualifies such continuous-variable entangled states, as shown successfully light fields. Here, we report on production which meet for continuous phase/amplitude variables. created ultracold atoms shows an parameter 0.18(3), is 2.4 standard deviations below threshold 1/4. Our presents...
Abstract Novel pyroelectric THz detectors have been developed in close cooperation between PTB, the National Metrology Institute of Germany, and Sensor- und Lasertechnik company. Covering broad spectral range from below 50 GHz to beyond 5 THz, these are suited measure absolute power time-domain spectroscopy (THz-TDS) systems for first time.
The effective hole masses of wurtzite GaN are determined experimentally by an all-optical method. Therefore, we measure interband transitions as a function the degenerate free-electron density and analyze different many-body contributions arising from Burstein–Moss effect band-gap renormalization. When known anisotropic electron mass is taken into account, shape valence band can be reconstructed. Here, nonpolar thin films doped with germanium or silicon at 9 × 1018 ≤ n 1.5 1020 cm−3...
Abstract Doping induced changes in lattice parameters are investigated experimentally for the shallow donors silicon and germanium thin-film wurtzite a-plane GaN. Silicon doping results a contraction while small but measurable expansion. By high-resolution x-ray diffraction, we able to determine isotropically averaged size-effect with high accuracy. The analysis procedure yields en passant phonon deformation potentials <?CDATA $c_\mathrm{E_1(TO)}$?> <mml:math...
We report on a new, general-purpose particle detector consisting of stretched foil PVDF for use in pulsed supersonic jet experiments. The signal is analyzed detail, allowing to exploit both the piezo- and pyroelectric effects.
PTB, the metrology institute of Germany, operates worldwide first and still unique THz detector calibration facility traceable to International System Units. A research development project in cooperation with a manufacturer pyroelectric detectors is dedicated develop suitable detectors.
Absolute power measurements are crucial for the development of mm-wave sources and their safe operation. In a French-German research project, we developing detector absolute frequencies between 220 330 GHz (WR-3 band). This is designed to measure radiation emitted from suitable horn antenna. We also method its calibration at German National Metrology Institute (PTB). Our work will contribute worldwide efforts communication radar applications.
If the boundary conditions of quantum vacuum are changed in time, field theory predicts that real, observable particles can be created initially empty modes. Here, we realize this effect by changing a spinor Bose-Einstein condensate, which yields population unoccupied spatial and spin excitations. We prove excitations as entangled excitation pairs certifying continuous-variable entanglement within many-particle output state.
Spectroscopic ellipsometry is applied for determining the ordinary and extraordinary dielectric functions of wurtzite GaN different free-electron concentrations. The analysis in infrared spectral range yields frequencies coupled longitudinal plasmonphonon modes. From related plasma anisotropy effective electron mass determined. data ultraviolet indicate unambiguously that L-valley conduction band undoped material located at least ≈ 2 eV above minimum Γ-point. In contrast to behavior Γ-point,...
This work presents a photolithographic rapid prototyping process for producing thin films ("Rapid Phototyping"). allows quick and cost-effective generation of scalable thermopile microstructures using commercial equipment materials. Structural widths 100x250μm can be produced reproducible in lift-off with an accuracy 5 microns vertically 30 horizontally.
Novel pyroelectric THz detectors were calibrated traceable to SI and applied for precise power measurements of time-domain spectroscopy systems an international pilot comparison.
Machining high temperature superconducting (HTS) thin films is challenging due to the material's sensitivity. Here, 200 nm thick YBCO microbridges were machined with a femtosecond laser (300 fs at 1030 wavelength) as chemical free and flexible method minimal edge damage. Transport measurements Raman spectroscopy used analyse bridges before after processing. While transport are commonly separately evaluate YBCO, our approach links both techniques induced The link between changes in spectrum...
We present a THz thin-film attenuator with 35 dB power attenuation suitable to evaluate the linearity of time-domain spectroscopy system.