Fig. 1. Terahertz electron acceleration using cylindrical waveguide and tapered parallel-plate waveguide. (a) Cylindrical waveguide^[14]; (b) tapered parallel-plate waveguide^[53]

Fig. 2. Segmented and multi-period terahertz electron acceleration. (a) Segmented^[55]; (b) multi-period^[59]

Fig. 3. Schematic diagrams of millijoule level terahertz generation and high repetition rate terahertz radiation source based on wire waveguide. (a) Millijoule level terahertz generation^[61]; (b) high repetition rate terahertz radiation source^[62]

Fig. 4. Transmissive and reflective single grating electron acceleration. (a) Transmissive^[17]; (b) reflective^[66]

Fig. 5. Dual-grating and dual-pillar-grating electron acceleration. (a) Dual-grating^[70]; (b) dual-pillar-grating^[72]

Fig. 6. Cascaded grating electron acceleration and diagnosis of electric field distribution inside grating. (a) Cascaded grating electron acceleration^[74]; (b) diagnosis of electric field distribution^[75]

Fig. 7. Electron beam compression by terahertz waves using different functional structures. (a) STEAM^[33]; (b) parallel-plate waveguide^[34]

Fig. 8. Spatial focusing and lateral deflection of electron beams. (a) Focusing by parabolic grating^[74]; (b) streaking based on grating structure^[85]; (c) terahertz oscilloscope using elliptically polarized terahertz pulses^[86]

Fig. 9. AXSIS scheme^[29,89]. (a) Schematic of electron source; (b) overall scheme design of accelerator

Fig. 10. All-optical terahertz accelerator configuration proposed by Tsinghua University^[90]