Fig. 1. Physical aperture near-field imaging. (a) Illumination mode^[22]; (b) collection mode^[23]

Fig. 2. Conical surface cycle structures. (a) Bull′s-eye structure^[26]; (b) bow-tie structure^[27]

Fig. 3. Waveguide structures. (a) Variable-gap tapered waveguide^[28]; (b) silver-plated polycarbonate flexible waveguide with aperture diameters of 1.6‒2.6 mm^[29]

Fig. 4. Dynamic aperture near-field imaging. (a) Photo-excited carrier dynamically modulated THz beam system^[30]; (b) THz dynamic aperture system based on two-color air plasma filament^[34]; (c) THz-TDS-based femtosecond laser filament-forming dynamic aperture system^[36]; (d) THz dynamic aperture system based on crossed filament^[37]

Fig. 5. THz scattering scanning near-field optical system^[55]. (a) Schematic diagram of the equipment; (b) schematic diagram of the needle tip

Fig. 6. PCAM^[71]. (a) Photograph of a conical PCAM mounted on a wedge-shaped object tilted at 30°; (b) schematic of the probe tip at the top, and zoomed-in probe tip area at the bottom

Fig. 7. Schematic of PCAM-based experimental setup for THz near-field imaging^[74]

Fig. 8. THz scanning tunneling microscope schematic diagram^[77]. (a) THz pulses focused on the scanning tunneling microscope tip; (b) THz pulses incident at an angle higher than horizontal to the scanning tunneling microscope tip

Fig. 9. Schematic diagram of near-field superlens^[87]. (a) Superlens model; (b) equivalent model at a specified frequency

Fig. 10. Schematic diagram of the principle of THz real-time imaging^[92]

Fig. 11. Materials and moving carriers identified by THz near-field imaging and infrared near-field imaging^[93]. (a) AFM direct imaging; (b) THz near-field image acquired simultaneously with AFM imaging; (c) infrared near-field image

Fig. 12. THz intensity plots at different temperatures^[94]

Fig. 13. Schematic of the imaging of the Bi₂Se₃ and Bi₂Te_2.2Se_0.8 flake samples^[97]. (a) Near-field imaging of Bi₂Se₃ and Bi₂Te_2.2Se_0.8 flakes with different thicknesses; (b) fifth-order self-mixed-signal imaging of Bi₂Se₃ and Bi₂Te_2.2Se_0.8 flakes with different thicknesses

Fig. 14. AFM and THz s-SNOM images of immunoglobulin G molecules^[99]. (a) AFM image; (b) THz s-SNOM image

Fig. 15. AFM and THz s-SNOM images of Bacillus cereus and 2019-nCoV^[100]. (a) Bacillus cereus; (b) 2019-nCoV

Fig. 16. AFM and THz s-SNOM images of E. coli and S. aureus^[101]. (a1) (b1) (c1) are the AFM topographic map, AFM amplitude image, and THz near-field amplitude (top) and phase (bottom) images of E. coli; (a2) (b2) (c2) are the AFM topographic map, AFM amplitude image, and THz near-field amplitude (top) and phase (bottom) images of S. aureus

Fig. 17. THz near-field images of individual watermelon pulp cell during natural dehydration^[104]

Fig. 18. THz near-field images of mouse brain tissue^[106]. (a) Image of mouse brain tissue section; (b) stratification of corpus callosum and brain regions

Fig. 19. Near-field imaging images of normal liver tissue and hepatocellular carcinoma tissues and corresponding stained sections for pathologic microscopy^[107]. (a) Near-field imaging images; (b) stained sections

Fig. 20. Tissue with tumor and healthy tissue of human colon and corresponding stained sections for pathologic microscopy^[108]. (a) Near-field imaging marking results; (b) stained sections

Fig. 21. THz images and spectra of normal and cancerous tissues of oral tissues^[110]. (a) Histopathological images (① is normal epithelial tissue; ② is connective tissue; ④ is cancerous epithelial tissue); (b) refractive index images of the corresponding tissues at 1.2 THz; (c) absorption coefficient images of the corresponding tissues at 1.2 THz (dotted lines in the figure delineate the oral tissues with different components)

Fig. 22. THz-TDF hyperspectral nano-imaging of historical pigments^[116]. (a) Photograph of an ancient painted terracotta figurine; (b) is the optical image of an embedded sample prepared from the sculpture in (a); (c) is the electron microscope elemental image of the region marked by the dotted box in (b); (d) is the topographic image of the region marked by the dotted box in (c); (e) is the near-field white light image of the region marked by the dotted box in (c)