Terahertz spectroscopy

Terahertz spectroscopy refers to spectroscopic techniques that probe materials using electromagnetic radiation in the terahertz (THz) region, typically from ~0.1 to 10 THz (3 mm–30 μm). THz spectroscopy accesses low-energy excitations such as rotational and vibrational transitions in molecules, phonons and collective modes in solids, charge transport in semiconductors and superconductors, and intermolecular interactions in liquids and biomaterials.

Two major approaches are used: time-domain terahertz spectroscopy (THz-TDS), which employs pulsed THz radiation and waveform sampling, and frequency-domain terahertz spectroscopy (THz-FDS), which uses continuous-wave radiation and sweeps frequency. THz-TDS provides broadband access to amplitude and phase information and is widely used for materials characterization, imaging, and non-destructive evaluation. THz-FDS offers extremely high spectral resolution, often below 1 MHz, enabling Doppler-limited gas-phase spectroscopy, rotational spectroscopy, and precision metrology.

THz spectroscopy has applications in condensed-matter physics, chemistry, atmospheric and environmental sensing, security screening, pharmaceuticals, telecommunications, cultural-heritage analysis, biomedical imaging, and industrial quality control. THz systems can operate in free-space or waveguide geometries and may employ photoconductive emitters and detectors, nonlinear optical generation, photomixing, electronic sources, or quantum cascade lasers.

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