Terahertz spectroscopy and imaging techniques in practice

Terahertz (THz) waves (frequency: 0.1~10 THz; 3 to 300 cm^-1; wavelength: 30 μm to 3 mm) which exist between radio waves (electronics) and lights waves (optics), as shown in Fig. 1. They are perfectly non-invasive, and can penetrate opaque materials. As in infrared bands, fingerprint spectra of substances appear in THz frequency region, and the spectral features depend on molecular and intermolecular behaviour. The peaks correspond to weak bonds such as hydrogen bonds. [1,2] There are promissing reserach activities in Japan and Germany for polymer composites investigations by spectroscopy [3-8]. Fig. 2 shows the comparison of various calcium caobonate. Although they were all CaCO₃, the microscopic difference affects each spectra.