Frontiers in Terahertz Imaging Applications beyond AbsorptionCross-Section and Diffraction Limits

Abstract

Label-free imaging technology is highly desirable for various bioengineering,medicine, and chemistry applications. Most existing optical imaging techniques requirelabeling of the biospecimens and have limitations that may affect the intrinsic properties ofthe target species. The electromagnetic waves in the terahertz (THz) spectral range can be anexcellent alternative to visible light, which provides plentiful vibrational signatures of manymolecules with very low photon energy (1 THz is equivalent to 4 meV), completely free fromdamage to the biomaterials. For this reason, THz waves possessing a broadband spectrumhave emerged as a critical technology for fundamental research in bio/chemical detection andmedical imaging, as well as in solid-state physics, chemistry, material science, and highlyanticipated 6G next-generation telecommunications. The limited performance of THz waves as a sensing or imaging tool has been aconsiderable drawback resulting from low sensitivity or diffraction-limited low spatial resolution. Nevertheless, many successes inobtaining increased sensitivity with additional nanostructures and improving spatial resolution with geometric beam shaping openedup a way for highly efficient real-time THz imaging. From this Perspective, recent trends in innovative THz sensing and imagingresearch deserve an introduction regarding the level of reliability and sensitivity that can evolve into an actual medical device andother applications. It can also be expected to enable progress in analysis algorithms (compressive phase retrieval, reconstruction, ormachine/deep learning), enabling better data sampling, denoising, deblurring, and efficient computing cost, thusfinally providing aleap forward in the THz imaging area beyond the absorption cross-section and diffraction limits.