THz Spectroscopy

Terahertz radiation (THz) is a general term for electromagnetic waves in the 0.1-10 THz range. In imaging applications, this range is sometimes referred to as T-rays. A frequency of 1 THz corresponds to a wavelength of 300 µm (0.3 mm) and a wavenumber of 33 cm-1. THz fields span wavelengths from 3 mm (0.1 THz, or 100 GHz) down to 30 µm (10 THz). This interval lies between the upper edge of the millimeter-wave spectrum and the lower edge of the optical spectrum, corresponding to the boundary of the far-infrared (FIR) region.

Short THz pulses are most commonly used for Fourier absorption and reflection spectroscopy. The absorption spectra of many polar molecules, such as H2O, N2, O2, O3, HCl, CO, SO2, and CH3CN, contain distinct peaks in the THz range. These unique spectral signatures are highly important for environmental monitoring, air-pollution detection, gas sensing, and the detection of drugs and explosives.