Publications Search Results

Now showing 1 - 10 of 14
  • Publication
    Quantenkaskadenlaser-Spektrometer für die schnelle und artefaktfreie Abgasanalyse
    ( 2012)
    Brunner, R.
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    Lambrecht, A.
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    Herbst, J.
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    Heubuch, A.
    ;
    Jacob, E.
  • Publication
    Acetylene measurement using quantum cascade lasers at 14 µm
    ( 2011)
    Herbst, J.
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    Scherer, B.
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    Singer, F.
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    Erb, J.
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    Lambrecht, A.
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    Rathke, C.
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    Filip, S.
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    Kappler, J.
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    Fuchs, P.
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    Koeth, J.
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    Friedl, J.
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    Schlereth, T.W.
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    Semmel, J.
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    Höfling, S.
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    Worschesch, L.
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    Forchel, A.
    The monitoring of acetylene (C2H2) concentrations is important for many chemical processes. Industrial trace gas measurements are usually performed using gas chromatographs (GC) which have time constants of several minutes. Optical analyzers are expected to yield faster response times with lower maintenance costs. We investigated the use of quantum cascade laser (QCL) spectroscopy in the 14µm range for the sensitive and fast detection of C2H2. This spectral range is favorable, as it avoids spectral interferences by other components which could be present in typical process gases. We developed new custom DFB QCLs and characterized their spectral properties. We determined the performance of our QCL gas analyzer setup and demonstrate a noise equivalent concentration of 10 ppb in 20 s ave rage time.
  • Publication
    Acetylene measurement using quantum cascade lasers at 14 µm
    ( 2011)
    Herbst, J.
    ;
    Scherer, B.
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    Singer, F.
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    Erb, J.
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    Lambrecht, A.
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    Rathke, C.
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    Filip, S.
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    Kappler, J.
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    Fuchst, P.
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    Koeth, J.
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    Friedl, J.
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    Schlereth, T.W.
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    Semmel, J.
    ;
    Höfling, S.
    It is necessary to control the production process of industrial gases within seconds to get a constant high gas quality. Here, the process gas chromatography with a response time of minutes is state of the art in trace gas monitoring. As an alternative, we developed and present here a spectroscopic trace gas analyzer for acetylene. Because of the given complex gas mixture in a future application an acetylene absorption line at 14μm is selected to avoid cross sensitivities to other gases. For this special wavelength range new quantum cascade lasers (QCL) emitting 380mW peak power at 5 % duty cycle were developed by Nanoplus and University of Würzburg. To achieve a detection limit in the ppb concentration range and weak cross sensitivities the system was optimized towards a high spect ral resolution of 0.013 cm-1. The laser wavelength and the acetylene absorption line are checked by FTIR spectroscopy. In first experiments with the quantum cascade laser spectrometer a noise equivalent concentration of 50ppb acetylene in 1s was achieved.
  • Publication
    Laser-Spektrometer für die optische Gasanalyse in der Prozessmesstechnik
    ( 2011)
    Herbst, J.
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    Scherer, B.
    ;
    Lambrecht, A.
    Fraunhofer IPM entwickelt Gasanalysatoren auf Basis der Laserabsorptionsspektroskopie für Anwendungen in der Prozessmesstechnik und Raumluftüberwachung. Es wird die Entwicklung eines Prozessgasanalysators für Acetylen in einer komplexen Gasmatrix vorgestellt. Für das Spektrometer auf Basis eines Quantenkaskadenlasers (QCL), der im Bereich von 14 μm Wellenlänge emittiert, wurde die Interpulsmethode so ausgearbeitet, dass Pyrodetektoren verwendet werden können. Das System zeigt eine Nachweisgrenze von 10 ppb C2H2 in N2 für 20 s unter den Betriebsbedingungen (15 m, 50 mbar, 313 K). Die Separierung der Absorptionslinie in der Gasmatrix gelingt mit der hohen spektralen Auflösung von 0,01 cm-1. Es wird des Weiteren die Methode der direkten kalibrationsfreien Laserspektroskopie anhand eine s Spektrometers für O2, CO und HCL auf Basis von VCSEL (Vertical Cavity Surface Emitting Laser) vorgestellt. Diese Methode findet ihre Anwendung dort, wo eine hohe Genauigkeit bei stark schwankenden Betriebsbedingungen und langen Wartungsintervallen benötigt werden. Mit dem System werden Nachweisgrenzen von 48 ppm für O2, 0,6 ppm für CO und 0,14 ppm für HCL erreicht.
  • Publication
    TATP and TNT detection by mid-infrared transmission spectroscopy
    ( 2009)
    Herbst, J.
    ;
    Hildenbrand, J.
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    Wöllenstein, J.
    ;
    Lambrecht, A.
    Sensitive and fast detection of explosives remains a challenge in many threat scenarios. Fraunhofer IPM works on two different detection methods using mid-infrared absorption spectroscopy in combination with quantum cascade lasers (QCL). 1. stand-off detection for a spatial distance of several meters and 2. contactless extractive sampling for short distance applications. The extractive method is based on a hollow fiber that works as gas cell and optical waveguide for the QCL light. The samples are membranes contaminated with the explosives and real background. The low vapor pressure of TNT requires a thermal desorbtion to introduce gaseous TNT and TATP into the heated fiber. The advantage of the hollow fiber setup is the resulting small sample volume. This enables a fast gas exchange rate and fast detection in the second range. The presented measurement setup achieves a detection limit of around 58 ng TNT and 26 ng TATP for 1 m hollow fiber. TATP - an explosive with a very high vapor pressure in comparison to TNT or other explosives - shows potential for an adequate concentration in gas phase under normal ambient conditions and thus the possibility of an explosive detection using open path absorption of TATP at 8 μm wavelength. In order to lower the cross sensitivities or interferents with substances with an absorption in the wavelength range of the TATP absorption the probe volume is checked synchronously by a second QCL emitting beside the target absorption wavelength. In laboratory measurements a detection limit of 5 ppm*m TATP are achieved.
  • Publication
    Optical stand-off detection of explosives and improvised explosive devices - OFDEX
    ( 2009)
    Schnürer, F.
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    Schweikert, W.
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    Heil, M.
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    Bunte, G.
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    Krause, H.
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    Fuchs, F.
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    Kaster, J.
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    Hinkov, B.
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    Yang, Q.K.
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    Bronner, W.
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    Köhler, K.
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    Wagner, J.
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    Jander, P.
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    Fricke-Begemann, C.
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    Noll, R.
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    Hildenbrand, J.
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    Herbst, J.
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    Degreif, K.
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    Lambrecht, A.
    The Fraunhofer Society pooled its know-how in the fields of explosives, laser spectroscopy, semiconductor-laser design and system integration in order to develop optical technologies for the stand-off detection of explosives. Within the framework of a comprehensive research and development project called OFDEX, four Fraunhofer institutes are working jointly towards the development of a demonstrator remote detection system. Many explosives can be detected because they exude gas which may form a "vapour cloud" (plume) above a potential assassin. Moreover, as most explosives are absorbed well by surfaces of many kinds, it is likely that persons (e.g. their clothing) or parts of cars (e.g. door handles) will be contaminated, a fact that is similarly useful in remote detection. For both detection scenarios (gas phase and traces on surfaces) very small quantities of explosives must be detected. However, the concentrations necessary in practice are largely unknown. Using experimental methods and mathematical modelling, the Fraunhofer ICT aims to determine the dispersion of explosive gases and particle traces. Particular emphasis is placed on the dispersion behaviour of the substances used in so-called Improvised Explosive Devices (IEDs). The Fraunhofer IAF developed a new type of spectrally-tunable quantum cascade (QC) laser modules, which enables an increase of the tuning range by at least one order of magnitude in comparison to the established current-temperature tuning techniques. With the QC laser module it is possible to detect surface contaminations of around 10 µg/cm2 TNT performing imaging backscattering spectroscopy. The Fraunhofer IPM achieves a detection limit of 5 ppm*m for TATP-detection in the gas phase with a special measurement set-up. The Fraunhofer ILT is able to detect ANFO and TNT at surface coverage levels of 100 µg/cm2 against backgrounds of both organic and inorganic materials with remote Raman spectroscopy.
  • Publication
    Ultrafast protein conformational alterations in bacteriorhodopsin and its locked analogue BR5.12
    ( 2009)
    Gross, R.
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    Schumann, C.
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    Wolf, M.M.N.
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    Herbst, J.
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    Diller, R.
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    Friedman, N.
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    Sheves, M.
    Bacteriorhodopsin, reconstituted with a sterically "locked" retinal chromophore, BR5.12, has frequently been used to elucidate elementary photoinduced processes in the native pigment bacteriorhodopsin. In this work, the vibrational response of BR5.12 to photoexcitation is investigated by means of femtosecond time-resolved mid-infrared and UV-vis spectroscopy. The electronically excited state of BR5.12 decays with a time constant of 18 ps. Neither in the UV-vis nor in the mid-IR spectral region are indications found for chromophore photoproducts, besides the full recovery of the electronic ground state. However, vibrational bands are observed at around 1660 and 1550 cm-1 in the protein amide I and amide II band regions, respectively. They are formed within a few picoseconds or even instantaneously. Thus, they appear faster than the Si decay and persist for at least 130 ps, i.e., for much longer than the Si lifetime. These findings strongly suggest that the observed bands must be assigned to protein vibrations and that they are not caused by a photoinduced temperature rise. Thus, for the first time, ultrafast protein vibrational changes are detected in BR5.12, that are not associated with isomerization. Possibly they can be related to the enhanced chemical reactivity of photoactivated BR5.12 reported in the literature. In wild-type bacteriorhodopsin, bands with very similar spectral and kinetic characteristics are observed, suggesting that they might originate from a similar mechanism which is not isomerization. A plausible mechanism is a polarization induced protein conformational change, as discussed in the literature.
  • Publication
    Pressure broadening of the oxygen A-band measured by laser absorption spectroscopy
    ( 2009)
    Scherer, B.
    ;
    Herbst, J.
    Spectroscopic concentration measurements of oxygen at high pressures are limited by the effect of pressure broadening and line mixing. These effects strongly depend on the gas mixture in which the oxygen concentration has to be determined as the pressure broadening coefficients of different gases vary over a large range. Line broadening coefficients of the oxygen a-band for a large number of different gases are well known in the literature, but up to now there is, to our best knowledge, no experimental data available which describes the line broadening of oxygen in hydrogen. In respect to a possible application for online-monitoring of oxygen in hydrogen electrolysis we have measured the pressure broadening coefficient of the oxygen P9P9 line in hydrogen and compared with the theoretical m odel. To confirm the result, also measurements of the well known broadening coefficient of oxygen in helium were accomplished. Measurements were obtained using laser absorption spectroscopy with vertical-cavity surface-emitting lasers in a Herriott-Cell with 15 m path length adapted for vacuum pressures.
  • Publication
    Explosive detection using infrared laser spectroscopy
    ( 2009)
    Hildenbrand, J.
    ;
    Herbst, J.
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    Wöllenstein, J.
    ;
    Lambrecht, A.
    Stand-off and extractive explosive detection methods for short distances are investigated using mid-infrared laser spectroscopy. A quantum cascade laser (QCL) system for TATP-detection by open path absorption spectroscopy in the gas phase was developed. In laboratory measurements a detection limit of 5 ppm*m was achieved. For explosives with lower vapor pressure an extractive hollow fiber based measurement system was investigated. By thermal desorption gaseous TATP or TNT is introduced into a heated fiber. The small sample volume and a fast gas exchange rate enable fast detection. TNT and TATP detection levels below 100 ng are feasible even in samples with a realistic contaminant background.
  • Publication
    DFB laser diodes and quantum cascade lasers for sensors in safeguard applications
    ( 2008)
    Seufert, J.
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    Fischer, M.
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    Legge, M.
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    Roessner, K.
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    Werner, R.
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    Hildenbrand, J.
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    Herbst, J.
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    Lambrecht, A.
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    Koeth, J.
    We present an overview of the current status of laser diodes used in remote sensing application including novel laser types such as single mode emitting DFB lasers operating at wavelengths up to 3 µm and quantum cascade lasers for mid infrared absorption spectroscopy. In particular we will focus on applications of these devices in the frame of safeguard measures and home security.