An Introduction to THz-Raman Spectroscopy

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The terahertz (THz) region of the electromagnetic spectrum, from roughly 0.15 THz to 6 THz (5 cm-1 to 200 cm-1), has long been researched as a means of investigating low-energy vibrational modes of materials. This region is particularly attractive to spectroscopists studying intermolecular vibrations within crystals [1], yielding important information about the molecular orientation that governs many key properties of materials. On the most fundamental level, THz spectroscopy is an extension of far-infrared (FIR) absorption spectroscopy. In practice, it is far more challenging to implement because it is at the extreme low-end of the optical frequency domain and extreme high-end of the frequency domain for electronics. That is why this region of the spectrum is often referred to in the published literature as the “terahertz gap” [2]. Currently, commercial THz spectroscopy systems are available on the market, but most are extremely expensive and difficult to use due to the complexity of the ultrafast lasers typically required to generate THz radiation and susceptibility of samples to moisture.