1 <h5>Introduction</h5> The term “terahertz wave” is typically used to describe an electromagnetic wave with a frequency ranging between 0.1 and 10 THz (1 THz approximately equals 33 cm −1 ). It is well known that water strongly absorbs terahertz waves. Although the large extinction coefficient makes it difficult to use terahertz spectroscopy to investigate aqueous solutions or living tissues, some new techniques, such as visualization of the water distribution in a concrete block  or a thin seed  , have been realized. In this study, we acquired the terahertz transmission spectra of coal for the first time. By comparing spectra of coal both before and after a drying procedure, the influence of the water content in the coal was determined.</P>2 <h5>Material and methods</h5> 2.1 <h5>Terahertz spectrometer</h5> The terahertz spectrometer TSS-I (Terahertz Laboratory Co. Ltd., Akita, Japan) was used in this study. A coherent terahertz wave was emitted from a GaP crystal via difference frequency generation with two 1.2-μm band Cr:forsterite Lasers [3–6] . The spectrometer can sweep the frequency from 0.5 to 6.2 THz, and the line width is approximately 30 GHz (1 cm −1 ). In this study, the range was limited to 1.0–5.0 THz,
Fuel – Elsevier
Published: Mar 1, 2013
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