Fig. 1. Terahertz point-by-point scanning imaging^[5]. (a) Schematic diagram; (b) THz image of a semiconductor integrated circuit chip package; (c) THz image of the blade in different states

Fig. 2. Mathematical model of encoding mask design and image reconstruction

Fig. 3. Schematic of a terahertz single-pixel imaging optical path system based on different light sources. (a) Pulsed light source^[18];(b) continuous light source^[19]

Fig. 4. Terahertz single-pixel imaging based on metal masks. (a) PCB mask^[24]; (b) rotating metal disc mask^[25]

Fig. 5. Terahertz single-pixel imaging based on TPO^[26]. (a) Imaging schematic; (b) ‒(d) optical images of a round hole with a diameter of 2 mm, a rectangle with size of 3 mm × 3.5 mm, and the letter "H" with size of 8 mm × 10 mm, respectively; (e) ‒(g) corresponding terahertz images, respectively

Fig. 6. Electronically controlled metasurface mask based on active semiconductor. (a) 4×4 array metamaterial terahertz modulation mask^[30]; (b) terahertz metamaterial absorber^[31]; (c) 8×8 array metamaterial terahertz modulation mask^[32]

Fig. 7. Electronically controlled metasurface masks based on other tunable materials. (a) Electronically controlled graphene reflection modulator array^[35]; (b) graphene-based modulator arrays integrated on printed circuit boards^[36]; (c) VO₂-based 8×8 modulation array^[37]; (d) dual-color terahertz modulator based on liquid crystal^[38]

Fig. 8. Terahertz imaging based on light-induced semiconductor dynamic masks. (a) (b) Terahertz imaging schematic based on DMD and LED light sources and imaging results using 63, 105, 1023 pixel masks^[31]; (c) (d) compressed terahertz single-pixel imaging system using IFD algorithm and corresponding terahertz images reconstructed based on CS and IFD algorithms^[41]

Fig. 9. Single-pixel imaging system based on total internal reflection terahertz^[48]

Fig. 10. Near-field terahertz single-pixel imaging. (a) Schematic of terahertz single-pixel imaging system based on semiconductor silicon^［16］; (b) schematic of terahertz single-pixel imaging system based on VO₂^［17］