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Eingeladener Vortrag
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THz stand-off detection of explosives and other hazardous liquids in public areas becomes more and more relevant and with it the knowledge of their optical properties. We present here both the results of THz transmission spectroscopy measurements and spectroscopic ellipsometry measurements on liquids and their mixtures.
THz and Mid IR Fourier Transform Spectroscopy on Polyethylene Irradiated with Gamma- Co60 Radiation
(2014)
THz and Mid IR Fourier transform spectroscopy on polyethylene irradiated with Gamma- Co60 radiation
(2014)
THz and mid IR spectroscopy of high molecular PE (HMW) and ultra high molecular PE (UHMW) reveals modifications of the molecular structure induced by γ-Co60 radiation. UHMW-PE and HMW-PE can be distinguished. The integral absorption in the B1u THz-region can quantitatively describe the amorphization of crystallinity. The formation of trans vinylene unsaturations and the decay of vinyl can be followed by mid IR spectroscopy
Elektromagnetische Wellen von 0.3 bis 6 Terahertz (THz) werden als
THz-Strahlung bezeichnet. Im elektromagnetischen Spektrum sind sie zwischen
Mikro-/Millimeterwellen und Infrarot angesiedelt. Der nicht ionisierende Charakter
und die Möglichkeit, Verpackungsmaterialen sowie Kleidung zu durchstrahlen, machen
die THz-Strahlung für bildgebende- und spektroskopische Anwendungen sehr
interessant. Besondere Aufmerksamkeit gilt der Zeitaufgelösten Terahertz-
Spektroskopie (THz-TDS) im Sicherheitssektor. Feste Spreng- und Gefahrenstoffe
sind vielfach bezüglich ihrer Transmissions- und Reflexionseigenschaften untersucht
worden, um sie anhand ihrer Fingerprints zu identifizieren. Moderne mit Glasfaser
ausgerüstete THz-TD-Spektrometer zeichnen sich im Vergleich zu konventionellen
Freistrahlgeräten durch höhere Flexibilität aus. In Zukunft werden diese auch als
Handheld-Geräte entwickelt, um eine Nutzung außerhalb des Laboratoriums zu
ermöglichen. Das glasfasergekoppelte Picometrix T-ray 2000 System der BAM
wurde in ein Zwei-Kreis Goniometer integriert. Probe und Detektor können unabhängig
voneinander bewegt werden. Eine schnelle Überführung der Transmissionsin
die Reflexionsanordnung und umgekehrt, ist möglich. Seit der Verwendung flüssiger
Brand- und Gefahrstoffe bei terroristischen Anschlägen ist das Interesse an der
Identifizierung im Sicherheitsbereich zunehmend gewachsen. Um zu überprüfen, ob
die THz-TDS für die spektrale Charakterisierung von Flüssigkeiten eingesetzt werden
kann, wurden Transmissions- und Reflexionseigenschaften repräsentativer Flüssigkeiten
und Flüssigkeitsgemische bestimmt. Polare Flüssigkeiten sind starke Absorber
im THz-Bereich. Ab einer Flüssigkeitsschichtdicke von ca. 1mm ist mit dem
THz-Spektrometer T-ray 2000 kein Signal stark polarer Flüssigkeiten mehr
detektierbar. Der Einsatz einer Messzelle mit variabler Schichtdicke (50 - 1000 .m)
war für die Bestimmung der Transmissionseigenschaften polarer Flüssigkeiten notwendig.
Anhand von Transmissions- und Reflexionsuntersuchungen an polaren sowie
unpolaren Flüssigkeiten werden die Möglichkeiten der THz-TDS zur berührungslosen
Identifizierung von Flüssigkeiten aufgezeigt.
Flüssige Gefahr- und Brennstoffe sowie explosive Flüssigkeiten werden mittels zeitaufgelöster Terahertz-Spektroskopie (THZ-TDS) in Analogie zu den in der zerstörungsfreien Werkstoffprüfung verwendeten Strategien untersucht. Verschiedene polare Flüssigkeiten (Alkohole, Aceton, Wasserstoffperoxid, Nitromethan), unpolare Flugzeug- und Kraftfahrzeugkraftstoffe sowie organische Lösungsmittel werden in der praxisrelevanten Reflexionsgeometrie berührungs- und zerstörungsfrei im Zeitbereich charakterisiert. Die Absorptions- und Brechungsindizes einer repräsentativen Auswahl von Flüssigkeiten wurden im Frequenzbereich zwischen 0.1 THz und 1.1 THz unter Verwendung der Transmissionsanordnung spektral ermittelt. Die Messkonfiguration wird für stark und schwach absorbierende Flüssigkeiten jeweils angepasst.
The far infrared refractive indices and the extinction coefficients of liquids can be obtained by means of spectroscopic ellipsometry in attenuated total reflection configuration. Such optical constants will contribute to a spectroscopic data base in the far infrared and terahertz spectral regions. The experimental implementation and the calibration procedure of the method are described in detail. The temperature dependency of the optical constants for water over a broad spectral range is exemplarily presented.
Removal of Etalon Features in the Far-Infrared–Terahertz Transmittance Spectra of Thin Polymer Films
(2020)
Etalon features in infrared spectra of stratified samples, their influence on the interpretation and methods to circumvent their presence in infrared spectra have been in discussion for decades. This paper focuses on the application of a method originally developed to remove interference fringes in the mid-infrared spectra for far-infrared Fourier transform spectroscopy on thin polymer films. We show that the total transmittance-reflectance technique, commonly used for mid-infrared, also works successfully in the far infrared spectral range where other approaches fail. Experimental spectra obtained by such technique are supported by model calculations and reveal the possibility and limits to obtain almost undisturbed far-infrared spectra which are suitable to determine low energy vibrations of ionomer salts under certain sample conditions.
Optical constants of harmful and highly energetic liquids for application to THz screening systems
(2016)
The far-infrared (IR) optical constants of a set of hazardous and flammable liquids have been obtained by means of spectroscopic ellipsometry in attenuated total reflection configuration over a broad spectral range. Such liquids recently became of considerable concern for transportation security measures worldwide. Their optical identification at check-in gates can only become possible if the characteristic spectra are already known. The refractive indices and the extinction coefficients reported here contribute to a spectroscopic data base in the far-IR and terahertz (THz) spectral regions and may support modeling the performance of THz screening systems on liquids for airports and other security sensitive areas. Examples of several container material/liquid systems are discussed. From the measured optical constants typical THz waveforms are calculated and discussed.
Novel Technique for On-Line Monitoring of the Curing Process of Fiber Reinforced Polymer Composites
(2021)
A specially developed experimental set up has been integrated into a commercially available FT IR Spectrometer to study the curing of Epoxy Systems. MIR and FIR spectra measured during the curing process at different temperatures of an epoxy system will be presented in dependency of the curing time. The experiments and the selected set up are discussed to demonstrate its potential for future monitoring and ageing control applications during a manufacturing process of polymer composites.
The Dead Sea Scrolls belong to the most important cultural assets of mankind. Their long term preservation and study is a challenge that demands an interdisciplinary approach. As early as the 1950s natural scientists assisted the scholars in studying the scrolls. It was at this time that the first extensive study of the scroll material took place. It was found that most fragments were written not on leather but on parchment. In addition, a method for determining the age of the parchment was developed which is still of value today. In the 1990s the AMS-C14 method confirmed the palaeographic determination of the age of the manuscripts. The use of carbon ink throughout the scrolls is also consistent with the known scribal practices of that time. There are, however, manuscripts, and among them the famous Genesis Apocryphon Scroll, which exhibit ink corrosion, normally associated with iron-gall inks.
Today, 60 years after their discovery, a community of scientists from the Jewish National and University Library (JNUL), the Technical University of Berlin (TU Berlin), the Federal Institute for Materials Research and Testing (BAM) and Fritz-Haber-Institute of the MPG (FHI) set out to scientifically investigate the finds of Qumran using the most modern methods. The results of the study will be used to determine the provenance of the texts as well as to contribute to their long-term preservation. A considerable part of the non-destructive investigation is taking place in the Berlin State Library and at the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung , BESSY II.
Preliminary investigations, performed at the BAM on some fragments, were used to evaluate the extent to which X-ray analytical methods can provide information regarding the geographical origin of the fragments and match the individual pieces. The interpretation of the measurement results is made more difficult by age and storage of the objects. It is believed that ageing processes as well as conservation methods have altered the samples in addition to the changes caused by environmental influences.
In collaboration with the TU Berlin, the samples from the parchments found in the caves near Qumran were tested by means of three-dimensional synchrotron based X-ray fluorescence analysis (3D-SyXRF). The aim of this non-destructive investigation was the identification of the inorganic material used in the manufacture of the parchments.
The XRF experiments are supported by the non-destructive analysis by means of synchrotron based infrared spectroscopy (SyFTIR) in collaboration with BESSY II as well as optical and electron microscopy in collaboration with Fritz-Haber-Institute (FHI).