Spectroscopy terahertz

Terahertz, or far infrared spectroscopy, covers the frequency range from 0.1 to lOTHz (300 to 3cm ) where torsional modes and lattice vibrations of molecules are detected. It is increasing in use in many application areas, including analysis of crystalline materials. Several dedicated conunercial instruments are available which use pulsed terahertz radiation which results in better signal to noise than those using blackbody sources for radiation (and associated with the terminology far infrared spectroscopy). Work using extended optics of FTIR instrumentation as weU as continuous-wave source THz has also been recently reported.  

Examples of terahertz spectroscopy as a PAT tool in the pharmaceutical industry include monitoring of polymorphism, tablet coatings, and crystallinity, even at the stage of product development to aid in process design.  

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Waals modes in weakly-bound complexes has been discussed in section BT4. MicroM ave and Terahertz Spectroscopy, and will not be repeated here. 

Flame Photometry and Gas Chromatography (CyTerra) -Aerodynamic Particle Size and Shape Analysis (BIRAL) -Flow Cytometry (Luminex, LLNL) -Semiconductor-Based Ultraviolet Light (DARPA) -Polymer Fluorochrome (Echo Technology) -Laser-Induced Breakdown Spectroscopy -Raman Scattering -Infrared Absorption -Terahertz Spectroscopy -UV LIDAR... 

Parkinson P, Joyce HJ, Gao Q, Tan HH, Zhang X, Zon J, Jagadish C, Heiz LM, Johnston MB (2009) Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy. Nano Lett 9 3349... 

Parkinson P, Lloyd-Hughes J, Johnston MB, Herz LM (2008) Efficient generation of charges via below-gap photoexcitation of polymer-fiillerene blend films investigated by terahertz spectroscopy. Phys Rev B 78 115321... 

Nemec H, Nienhuys H-K, Perzon E, Zhang F, Inganas O, Kuzel P, Sundstrom V (2009) Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz spectroscopy. Phys Rev B 79 245326... 

Terahertz Spectroscopy Principles and Applications, edited by Susan L. Dexheimer... 

Terahertz spectroscopy Far-infrared spectroscopy 3D imaging X Polymorphism Coating integrity and thickness API distribution possible... 

Terahertz spectroscopy uses continuous wave (CW) and short pulsed laser excitation in the spectrum region between infrared and microwave frequencies. Pulsed laser excitation using pulse widths in the range of 10-100 femtoseconds has enabled the use of time-resolved terahertz spectroscopy, which is capable of capturing dynamic information at subpicosecond time scales. 

Markelz AG, Roitberg A, Heilweil EJ. Pulsed terahertz spectroscopy of DNA, bovine serum albumin and collagen between 0.1 and 2.0 THz. Chem Phys Lett. 2000 320(1-2) 42-48. 

Terahertz time-domain-spectroscopy has been used to distinguish between chiral and racemic hydrogen-bonded cocrystals, and could readily distinguish between the isostructural cocrystals of theophylline with the chiral and racemic forms of both malic and tartaric acids [29]. These findings are of importance since it was concluded that while the respective cocrystal systems were almost identical in molecular structure and supramolecular architecture, the use of terahertz spectroscopy was comparable in sensitivity to X-ray diffraction and more sensitive than Raman spectroscopy to changes in cocrystal architecture. Solid-state nuclear... 

E.P.J. Parrott, J.A. Zeitler, T. Friscic, M. Pepper, W. Jones, G.M. Day, L.F. Gladden, Testing the sensitivity of terahertz spectroscopy to changes in molecular and supramo-lecular structure a study of structurally similar cocrystals, Cryst. Growth Des. 9 (2009) 1452-1460. 

RESONANT TERAHERTZ SPECTROSCOPY OF BACTERIAL THIOREDOXIN IN WATER SIMULATION AND EXPERIMENT... 

For our terahertz transmission measurements, we used solutions of thioredoxin in distilled water obtained from Sigma. The experimental and simulated signatures are correlated and dominant peaks are close in frequencies. The results of this study demonstrate that terahertz spectroscopy is a promising tool in generating spectral data for cellular components of bio agents such as bacterial cells and spores. 

Additional experiments observing MEG have been reported for CdSe (Schaller et al., 2005b), PbTe (Murphy et al., 2006) and InAs (Pijpers et al, 2007). In addition to transient absorption studies, these optical experiments use time-resolved photoluminescence, terahertz spectroscopy, and quasi-CW spectroscopy. 

Transient terahertz spectroscopy Time-resolved terahertz (THz) spectroscopy (TRTS) has been used to measure the transient photoconductivity of injected electrons in dye-sensitised titanium oxide with subpicosecond time resolution (Beard et al, 2002 Turner et al, 2002). Terahertz probes cover the far-infrared (10-600 cm or 0.3-20 THz) region of the spectrum and measure frequency-dependent photoconductivity. The sample is excited by an ultrafast optical pulse to initiate electron injection and subsequently probed with a THz pulse. In many THz detection schemes, the time-dependent electric field 6 f) of the THz probe pulse is measured by free-space electro-optic sampling (Beard et al, 2002). Both the amplitude and the phase of the electric field can be determined, from which the complex conductivity of the injected electrons can be obtained. Fitting the complex conductivity allows the determination of carrier concentration and mobility. The time evolution of these quantities can be determined by varying the delay time between the optical pump and THz probe pulses. The advantage of this technique is that it provides detailed information on the dynamics of the injected electrons in the semiconductor and complements the time-resolved fluorescence and transient absorption techniques, which often focus on the dynamics of the adsorbates. A similar technique, time-resolved microwave conductivity, has been used to study injection kinetics in dye-sensitised nanocrystalline thin films (Fessenden and Kamat, 1995). However, its time resolution is limited to longer than 1 ns. 

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