Terahertz imaging technology: progress and applications

Terahertz imaging, operating within the 0.1–10 THz frequency range, leverages unique properties such as non-ionizing radiation, sensitivity to polar molecules, and material-specific spectral fingerprints. This review comprehensively surveys major terahertz imaging modalities, highlighting significant progress and applications. Key methodologies, including continuous-wave holography, lensless ptychography, and computed tomography, provide quantitative phase contrast and three-dimensional structural information. Notably, terahertz pulse time-domain holography leverages the broadband nature of pulsed sources to achieve depth-resolved imaging through time-gated analysis. The development of focal-plane and single-pixel imaging addresses challenges related to detector availability, enabling high-speed and cost-effective systems. A major breakthrough is observed in near-field imaging, which surpasses the diffraction limit to achieve nanoscale resolution for probing materials, biomolecules, and plasmonic phenomena. While challenges in signal-to-noise ratio, hardware integration, and imaging speed persist, ongoing innovations in laser sources, algorithms, and system design are driving adoption in security, biomedicine, and industrial inspection.