Time-domain terahertz

Nuss M C and Orenstein J 1998 Terahertz time domain spectroscopy Millimeter Submillimeter Wave Spectrosc. Solids 74 7-50... 

The observation of slow, confined water motion in AOT reverse micelles is also supported by measured dielectric relaxation of the water pool. Using terahertz time-domain spectroscopy, the dielectric properties of water in the reverse micelles have been investigated by Mittleman et al. [36]. They found that both the time scale and amplitude of the relaxation was smaller than those of bulk water. They attributed these results to the reduction of long-range collective motion due to the confinement of the water in the nanometer-sized micelles. These results suggested that free water motion in the reverse micelles are not equivalent to bulk solvation dynamics. 

Z. Zhang, Y. Zhang, G. Zhao and C. Zhang, Terahertz time-domain spectroscopy for explosive imaging , Optik 118 (2007) 325—329. 

Zhong Z, Gabor NM, Sharping JE et al (2008) Terahertz time-domain measurement of ballistic electron resonance in a single-walled carbon nanotube. Nat Nanotechnol 3 201-205... 

The main experimental elfects are accounted for with this model. Some approximations have been made a higher-level calculation is needed which takes into account the fact that the charge distribution of the trapped electron may extend outside the cavity into the liquid. A significant unknown is the value of the quasi-free mobility in low mobility liquids. In principle, Hall mobility measurements (see Sec. 6.3) could provide an answer but so far have not. Berlin et al. [144] estimated a value of = 27 cm /Vs for hexane. Recently, terahertz (THz) time-domain spectroscopy has been utilized which is sensitive to the transport of quasi-free electrons [161]. For hexane, this technique gave a value of qf = 470 cm /Vs. Mozumder [162] introduced the modification that motion of the electron in the quasi-free state may be in part ballistic that is, there is very little scattering of the electron while in the quasi-free state. 

Terahertz imaging approaches have typically used either short-pulsed laser or continuous wave (CW) THz generation and detection. The short-pulsed method usually involves the generation and detection of sub-picosecond THz pulses using either photoconductive antenna structures or optical rectification in a non-linear crystal. Pulsed sources seem to be more favorable (in particular for close proximity applications) because they can be used for acquiring depth information. Spectral information is retrieved by a Fourier transform of the time-domain data to the frequency domain. 

Fig. 4. Terahertz time-domain images from Zimdars et al. [92] (a) transmission through a briefcase, (b) a...

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... 

Fig. 4 Comparison of Zero-Field techniques to determine the Zero-Field Splitting in Mni2Ac. (a) Frequency Domain Magnetic Resonance Spectroscopy [105]. (b) Frequency Domain Fourier-Transform Terahertz Spectroscopy [88] (Schnegg, Personal communication), (c) Terahertz Time-Domain Spectroscopy, adapted from [102]. Used with permission. 2001 American Physical Society, (d) Inelastic Neutron Scattering, adapted from [106]. Used with permission. 1999 American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society...

Nguyen KL, Friscic T, Day GM, Gladden LF, Jones W. Terahertz time-domain spectroscopy and the quantitative monitoring of mechanochemical cocrystal formation. Nat Mater 2007 6 206-9. 

D. Grischkowsky, S. Keiding, M. van Exter, Ch. Fattiger Far-infrared time-domain spectroscopy with terahertz beams of dielectrics and semiconductors. J. Opt, Soc, Am. B 7, 2006 (1990)... 

P.Y. Han, G.C. Cho, X.C. Zhang Time-domain transillumination of biological tissues with terahertz pulses. Opt. Lett. 24, 242 (2000)... 

Han, P. Y., Tani, M., Usami, M., Kono, S., Kersting, R. and Zhang, X. A direct comparison between terahertz time-domain spectroscopy and far-infrared Fourier transform spectroscopy. /. Appl. Phys. 89 2357-2359, 2001. 

Figure 10.3 Typical terahertz time-domain waveform recorded at a single point on the surface of a coated tablet. The first reflection is due to the interface between air and the outer coating surface. The second peak corresponds to the interface between the inner coating layer and the tablet core. The scale is...

Figure 10.4 Terahertz time-domain waveform taken from a point on the surface of a double-coated tablet. The successive positive and negative peaks reflect each change in refractive index within the structure. The...

Far-Infrared Spectroscopy and Terahertz Time-Domain Spectroscopy... 

By comparison with the phrase far-infrared spectroscopy, the term terahertz spectroscopy or terahertz time-domain spectroscopy is a relatively recent one, which probably began to be used in the early 1990s. As was already described in Section 1.2.1, the wavenumber region of 400 to 10cm corresponds to the frequency region of (12-0.3) x 10 Hz... 

Far-Infrared Spectroscopy and Terahertz Time-Domain Spectroscopy 273 19.2.3 Spectral Measurements in the Far-Infrared Region... 

As the absorption bands caused by water vapor (its rotational spectrum) are intense throughout the far-infrared region, it is important to purge efficiently the inside of the spectrometer with dried air or nitrogen. Some commercial spectrometers can be evacuated, but usually their sample compartment needs to be purged with dried air or nitrogen. This is commonly needed also in terahertz time-domain spectrometry, which is described in the following section. 

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