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Morris CM, Stehr D, Kim H, Truong TA, Pryor C, Petroff PM, Sherwin MS. Terahertz ionization of highly charged quantum posts in a perforated electron gas. Nano Lett 2012; 12:1115-1120. [PMID: 21517124 DOI: 10.1021/nl1044154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
"Quantum posts" are roughly cylindrical semiconductor nanostructures that are embedded in an energetically shallower "matrix" quantum well of comparable thickness. We report measurements of voltage-controlled charging and terahertz absorption of 30 nm thick InGaAs quantum wells and posts. Under flat-band (zero-electric field) conditions, the quantum posts each contain approximately six electrons, and an additional ~2.4 × 10(11) cm(-2) electrons populate the quantum well matrix. In this regime, absorption spectra show peaks at 3.5 and 4.8 THz (14 and 19 meV) whose relative amplitude depends strongly on temperature. These peaks are assigned to intersubband transitions of electrons in the quantum well matrix. A third, broader feature has a temperature-independent amplitude and is assigned to an absorption involving quantum posts. Eight-band k·p calculations incorporating the effects of strain and Coulomb repulsion predict that the electrons in the posts strongly repel the electrons in the quantum well matrix, "perforating" the electron gas. The strongest calculated transition, which has a frequency close to the center of the quantum post related absorption at 5 THz (20 meV), is an ionizing transition from a filled state to a quasi-bound state that can easily scatter to empty states in the quantum well matrix.
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Affiliation(s)
- Christopher M Morris
- Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, USA.
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Bhattacharyya J, Wagner M, Zybell S, Winnerl S, Stehr D, Helm M, Schneider H. Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation. Rev Sci Instrum 2011; 82:103107. [PMID: 22047280 DOI: 10.1063/1.3653394] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect.
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Affiliation(s)
- J Bhattacharyya
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany.
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Krause J, Wagner M, Winnerl S, Helm M, Stehr D. Tunable narrowband THz pulse generation in scalable large area photoconductive antennas. Opt Express 2011; 19:19114-19121. [PMID: 21996852 DOI: 10.1364/oe.19.019114] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The generation and characterization of narrowband THz pulses by means of chirped pulse difference frequency generation in Auston-switch type photoconductive antennas is reported. Using optical pulses with energies in the range from 1 nJ to 1 µJ, we generate THz pulses with up to 50 pJ in energy and electric field strengths on the order of 1 kV/cm. Two emitter concepts are investigated and circumvention of the fast saturation for small area excitation by scaling of the THz emitter is demonstrated.
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Affiliation(s)
- Johannes Krause
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden Rossendorf, P.O. Box 510119, 01314 Dresden, Germany
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Abstract
We have developed a rapid scanning terahertz (THz) spectrometer based on a synchronized two-fiber-laser system. When the system is set to the asynchronous optical sampling mode, THz spectra extending to 3 THz can be acquired within 1 μs at a signal-to-noise ratio of the electric field of better than 20. Signal averaging results in a dynamic range of more than 60 dB, and frequency components of more than 4 THz can be detected. When the lasers are set to the same repetition rate, electronically controlled optical sampling at a rate of 2.5 kHz is demonstrated, making the system versatile for different spectroscopic applications. Finally, we compare the THz emission spectra of a photoconductive switch that is pumped at 780 nm and a nonlinear DAST crystal excited at 1550 nm. We find that the spectral range of the spectrometer is significantly enhanced at higher frequencies, while the dynamic range remains constant.
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Affiliation(s)
- Dominik Stehr
- Institute for Terahertz Science and Technology, University of California Santa Barbara, Santa Barbara, California 93106, USA.
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Wagner M, Schneider H, Stehr D, Winnerl S, Andrews AM, Schartner S, Strasser G, Helm M. Observation of the intraexciton Autler-Townes effect in GaAs/AlGaAs semiconductor quantum wells. Phys Rev Lett 2010; 105:167401. [PMID: 21231010 DOI: 10.1103/physrevlett.105.167401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Indexed: 05/30/2023]
Abstract
The near-infrared transmission of a semiconductor multiple quantum well is probed under intense terahertz illumination. We observe clear evidence of the intraexcitonic Autler-Townes effect when the terahertz beam is tuned near the 1s-2p transition of the heavy-hole exciton. The strongly coupled effective two-level system has been driven with terahertz field strengths of up to 10 kV/cm resulting in a Rabi energy of ≈0.6 times the transition energy. The induced near-infrared spectral changes at low intensities are qualitatively explained using a basic two-level model.
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Affiliation(s)
- Martin Wagner
- Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany
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Zibik EA, Grange T, Carpenter BA, Porter NE, Ferreira R, Bastard G, Stehr D, Winnerl S, Helm M, Liu HY, Skolnick MS, Wilson LR. Long lifetimes of quantum-dot intersublevel transitions in the terahertz range. Nat Mater 2009; 8:803-807. [PMID: 19684587 DOI: 10.1038/nmat2511] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 07/14/2009] [Indexed: 05/28/2023]
Abstract
Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to approximately 2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.
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Affiliation(s)
- E A Zibik
- [1] Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK [2] Present addresses: Oclaro (Switzerland) AG, Binzstrasse 17, CH-8045 Zürich, Switzerland (E.A.Z.); Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany (T.G.); Department of Electronic & Electrical Engineering, University College London, London WC1E 7JE, UK (H.Y.L.) [3] These authors contributed equally to this work
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Golde D, Wagner M, Stehr D, Schneider H, Helm M, Andrews AM, Roch T, Strasser G, Kira M, Koch SW. Fano signatures in the intersubband terahertz response of optically excited semiconductor quantum wells. Phys Rev Lett 2009; 102:127403. [PMID: 19392323 DOI: 10.1103/physrevlett.102.127403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Indexed: 05/27/2023]
Abstract
Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.
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Affiliation(s)
- D Golde
- Department of Physics and Materials Sciences Center, Philipps-University, Renthof 5, 35032 Marburg, Germany.
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Kehr SC, Cebula M, Mieth O, Härtling T, Seidel J, Grafström S, Eng LM, Winnerl S, Stehr D, Helm M. Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser. Phys Rev Lett 2008; 100:256403. [PMID: 18643683 DOI: 10.1103/physrevlett.100.256403] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 05/14/2008] [Indexed: 05/26/2023]
Abstract
We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal.
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Affiliation(s)
- S C Kehr
- Institute of Applied Photophysics, Technische Universität Dresden, D-01062 Dresden, Germany
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Stachel B, Christoph EH, Götz R, Herrmann T, Krüger F, Kühn T, Lay J, Löffler J, Päpke O, Reincke H, Schröter-Kermani C, Schwartz R, Steeg E, Stehr D, Uhlig S, Umlauf G. Dioxins and dioxin-like PCBs in different fish from the river Elbe and its tributaries, Germany. J Hazard Mater 2007; 148:199-209. [PMID: 17382467 DOI: 10.1016/j.jhazmat.2007.02.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Revised: 02/02/2007] [Accepted: 02/06/2007] [Indexed: 05/14/2023]
Abstract
In a long-term program polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) as well as dioxin-like polychlorinated biphenyls (DL-PCBs) were analyzed in the muscle tissue of eels (Anguilla anguilla), bream (Abramis brama), European chub (Leuciscus cephalus) and ide (Leuciscus idus) from the river Elbe and its tributaries Mulde and Saale. The variation of the PCDD/F and DL-PCB concentrations in all fish samples is very large, whereby the DL-PCBs predominate in comparison to the PCDD/Fs. In the eels, the concentrations (pg WHO-TEQ/g ww) for the PCDD/Fs lie in the range of 0.48-22 and for the DL-PCBs between 8.5 and 59. In the whitefish, the concentration range is 0.48-12 for the PCDD/Fs and 1.2-14 for the DL-PCBs. Statistical analysis using relative congener patterns for PCDD/Fs allow spatial correlations to be examined for sub-populations of eels and whitefish. The results are compared to the maximum levels laid down in the European Commission Regulation (EC) No. 466/2001 and the action levels of the European Commission Recommendation 2006/88/EC. Eels caught directly after the major flood in August 2002 as well as eels near Hamburg (years 1996 and 1998) show high concentration peaks. Compared to the eels whitefish is less contaminated with PCDD/Fs and DL-PCBs.
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Affiliation(s)
- B Stachel
- Behoerde fuer Stadtentwicklung und Umwelt, Amt fuer Umweltschutz, Abteilung Gewaesserschutz, Billstrasse 84, D-20539 Hamburg, Germany.
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Stehr D, Baumgarte J. [Quality management in animal welfare]. Dtsch Tierarztl Wochenschr 2007; 114:140-4. [PMID: 17484501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
In the EC since Jan. 1st 2006 the Regulation (EC) No 882/2004 requires also in the field of animal welfare uniform official controls of a consistently high quality on the basis of documented procedures. Rised demands for the administration necessitate nowadays an all-embracing conception and controlling of the system. Therefore the land of Lower Saxony developed an uniform process-oriented conception for all involved official authorities based on ISO 9001 (EQUINO -Uniform Quality Management in Official Organisations for Consumer Protection in Lower Saxony) and implemented it including a system of internal audits.
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Stachel B, Christoph EH, Götz R, Herrmann T, Krüger F, Kühn T, Lay J, Löffler J, Päpke O, Reincke H, Schröter-Kermani C, Schwartz R, Steeg E, Stehr D, Uhlig S, Umlauf G. Contamination of the alluvial plain, feeding-stuffs and foodstuffs with polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs) and mercury from the River Elbe in the light of the flood event in August 2002. Sci Total Environ 2006; 364:96-112. [PMID: 16199077 DOI: 10.1016/j.scitotenv.2005.07.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2005] [Revised: 07/07/2005] [Accepted: 07/09/2005] [Indexed: 05/04/2023]
Abstract
Meadow soils, feeding-stuffs and foodstuffs from the alluvial plain of the river Elbe were analyzed in respect of PCDD/Fs, DL-PCBs and mercury with a view to assessing the consequences of the extreme flood of August 2002. The PCDD/F concentrations in the soils range from 3 to 2100 ng WHO-TEQ/kg dm, and for the DL-PCBs the range was 0.32 to 28 ng WHO-TEQ/kg dm. On the basis of established threshold values >40% of the areas are only fit for restricted usage. Mercury concentrations range from 0.11 to 17 mg/kg dm, whereby the action value of 2 mg/kg dm is exceeded in about 50% of the soil samples. A cumulative memory effect from past floods rather than a recent contamination from August 2002 is documented. Soils taken from behind broken dykes showed significantly lower concentrations. Grass, hay and grass silage originating from pasture land in Lower Saxony were taken before and immediately after the flooding. PCDD/Fs range from 0.29 to 16 ng WHO-TEQ/kg, the maximum permitted value of 0.75 ng WHO-TEQ/kg was exceeded in about 50% of the samples. Muscle-tissue from cattle, sheep, lamb and a roe deer as well as untreated milk from individual cows returned values ranging from 0.76 to 5.9 pg WHO-PCDD/F-TEQ/g fat, and 10% of the samples returned values higher than the permitted maximum of 3 pg WHO-PCDD/F-TEQ/g fat. The action value of 2 pg WHO-PCDD/F-TEQ/g fat was exceeded in 33% of the samples. No direct connection between these results and the effects of the flood could be established. A major input path for PCDD/Fs is the tributary Mulde, which discharges contaminated sediments from its catchment area into the Elbe.
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Affiliation(s)
- B Stachel
- Wassergütestelle Elbe der Arbeitsgemeinschaft für die Reinhaltung der Elbe, Nessdeich 120-121, D-21129 Hamburg, Germany.
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Stehr D, Metzner C, Helm M, Roch T, Strasser G. Resonant impurity bands in semiconductor superlattices. Phys Rev Lett 2005; 95:257401. [PMID: 16384504 DOI: 10.1103/physrevlett.95.257401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Indexed: 05/05/2023]
Abstract
It is shown that the confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three-dimensional Hamiltonian for a quantum well system with random impurities. Intersubband absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, which also requires reinterpretation of previous data.
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Affiliation(s)
- Dominik Stehr
- Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, P.O. Box 510119, 01314 Dresden, Germany.
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Schulz AJ, Wiesmüller T, Appuhn H, Stehr D, Severin K, Landmann D, Kamphues J. Dioxin concentration in milk and tissues of cows and sheep related to feed and soil contamination. J Anim Physiol Anim Nutr (Berl) 2005; 89:72-8. [PMID: 15787974 DOI: 10.1111/j.1439-0396.2005.00547.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
If cows or sheep are grazing on areas known for a higher dioxin level of the soil, respectively, dry cows are fed with feedstuffs produced on such areas, the dioxin concentration in food, in this case in cows' milk and livers of sheep could reach or exceed maximum levels. Furthermore large amounts of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzo-p-furans (PCDD/F) can be excreted with the faeces. But there are chances for farmers to prevent or at least to minimize the dioxin load of feed and with it of food (including the harvesting technique and the feeding strategy).
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Affiliation(s)
- A J Schulz
- Institute of Animal Nutrition, University of Veterinary Medicine Hannover, Foundation, Bischofsholer Damm 15, D-30173, Germany.
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