Terahertz Spectroscopy

Abstract

Abstract Terahertz spectroscopy has attracted great interest in recent years due to the development of improved terahertz radiation sources and terahertz radiation detectors as well as novel terahertz spectroscopy systems. This article discusses Fourier transform far‐infrared spectroscopy, backward‐wave oscillator terahertz spectroscopy, and time‐domain terahertz spectroscopy. Terahertz spectroscopy is spectroscopy with electromagnetic radiation in the terahertz (THz) frequency range. THz radiation is invisible. The THz frequency range is located between microwaves and the infrared. THz spectroscopy measures the dielectric properties of liquid and solid as well as inorganic and organic materials in the THz frequency range. Furthermore, THz spectroscopy is a method for vibrational and rotational spectroscopy of gases. Specifications and merits of Far‐infrared Fourier transform spectroscopy, backward‐wave oscillator terahertz spectroscopy, and time‐domain terahertz spectroscopy for applications in analytical chemistry are compared. The frequency range, frequency resolution, and dynamic range of each method are discussed. Various measurement modalities such as transmission and reflection spectroscopy, phase‐sensitive spectroscopy, and time‐resolved THz spectroscopy are explained. The physical measurement principle of each method is discussed. The relationship between the measurement observed and the dielectric function of a material are presented for each method. Technical descriptions of the methods are provided. An overview on specific applications of THz spectroscopy is presented.