Fig. 1. Imaging system based on THz-TDS and its application^[14]. (a) Schematic of a two-dimensional transmission THz spectral imaging system based on THz-TDS system; (b) THz image of a semiconductor integrated circuit packaged by plastics; (c) THz image of a fresh leaf

Fig. 2. Pulsed THz imaging system and its application. (a) Schematic of pulsed THz wave focal line imaging system^[22]; (b) THz spectral images of tooth sample^[23]

Fig. 3. Schematic of THz-ATR imaging system based on THz-TDS^[9]

Fig. 4. THz polarization imaging. (a)‒(c) THz super-focusing under the illumination of right-hand polarization (RCP) light, linear polarization (LP) light, and left-hand polarization (LCP) light^[26]; (d) normalized distribution of superfocal spot along the x-axis of THz waves under different polarizations^[26]; (e) schematic of a multifocal metasurface lens with polarization rotation function^[27]; (f)‒(g) THz high-resolution images of samples at different focal points^[27]

Fig. 5. Continuous THz transmission imaging^[31]. (a) Schematic of THz transmission imaging system; (b) resolution of the imaging system measured by knife-edge method

Fig. 6. Schematic of continuous reflective THz imaging system based on solid immersion lens^[8]

Fig. 7. THz reflection and ATR imaging^[39]. (a) Schematic of common path continuous THz reflection and ATR imaging system; (b) resolution of continuous THz reflection and ATR imaging system when using imaging windows made of quartz and high resistance silicon materials

Fig. 8. Aperture-based THz near-field imaging. (a) Physical aperture-based THz near-field imaging^[55]; (b) dynamic aperture-based THz near-field imaging^[56]

Fig. 9. Tip-based THz near-field imaging^[43]. (a) Needle-type THz near-field imaging system; (b) THz near-field peak intensity image and AFM topography

Fig. 10. Micro-nano-structure-control-based THz near-field imaging. (a) Recognition of metal slits by double-layer graphene structure^[66]; (b) THz superlens with single-layer graphene structure^[67]; (c) graphene hyperbolic superlens based on sector modulation structure^[68]

Fig. 11. Schematic of THz pulse real-time imaging system based on electro-optic sampling method^[69]

Fig. 12. THz real-time imaging^[73]. (a) Schematic of THz real-time imaging system; (b) schematic of THz real-time imaging principle

Fig. 13. THz security inspection system. (a) THz security inspection system developed by Digital Barriers^[81]; (b) THz security inspection system developed by China Electric Power 38 Institute^[82]

Fig. 14. Application of THz imaging technology in non-destructive testing^[80]. (a) Schematic of reflective continuous THz imaging system; (b) schematic of transmission continuous THz imaging system; (c) photograph of the foam sample and defect map of the sample

Fig. 15. Current status of research on THz imaging detection for different biological tissues