Broadband Infrared Absorption Spectroscopy as a Tool for Dielectric Materials Research

Among various spectroscopic tools used in materials research, optical absorption spectroscopy is one of the most fundamental. Although mid-infrared (mIR) absorption spectroscopy is widely used, far-infrared (fIR) and THz absorption spectroscopy are not. This article shows that the use of all these spectroscopic tools is valuable for a deep understanding of materials, especially for dielectric materials. The reason for this is that the mIR photons are suitable to detect intramolecular vibrations or vibrations of a relatively small chemical group, whereas the fIR photons can detect vibrations of an entire molecule or those of a large chemical group. Furthermore, the THz spectroscopy is adequate to detect intermolecular vibrations. Several typical experimental results obtained by the authors, showing the above, are introduced.