Fig. 1. The photoconductive antenna generating terahertz wave

Fig. 2. Optical rectification generating terahertz wave

Fig. 3. Titled-pulse-front pump technique

Fig. 4. PCS-DSTMS crystals generating terahertz waves^[49]

Fig. 5. Difference frequency of DSTMS crystals generating terahertz wave^[64]

Fig. 6. Two-color field laser filaments generating terahertz waves^[75]

Fig. 7. Liquid water film generating terahertz wave^[13]

Fig. 8. Laser-solid target generating terahertz wave

Fig. 9. Mechanism of matter controlling of using high-filed terahertz wave^[86]. (a) High-field terahertz pulse; (b) vibration rotation,spin precession, and electron acceleration; (c) scheme diagram of time-resolved spectroscopy of high-field THz pump-optical probe

Fig. 10. Hot carrier extraction process in SnO₂/Sb₂Se₃ and CdS/Sb₂Se₃ heterojunctions^[110]. (a) Time-dependent photoinduced terahertz conductivity of Sb₂Se₃ with CdS and SnO₂ buffer layers; (b)(c) band diagrams of SnO₂/Sb₂Se₃ and CdS/Sb₂Se₃; (d) ultrafast time-dependent scattering time of SnO₂/Sb₂Se₃ and CdS/Sb₂Se₃; (e) decay time-dependent C parameter of SnO₂/Sb₂Se₃ and CdS/Sb₂Se₃

Fig. 11. Schematic diagram of femtosecond laser-induced topological insulator surface radiating broadband terahertz waves of different polarization directions^[117], where E_x is the displacement current radiation spectrum, and E_yz is the depletion current radiation terahertz spectrum

Fig. 12. Terahertz radiation enhancement induced by drift current amplification in WSe₂/Si heterojunctions^[121]. (a)‒(b) Time-domain spectroscopy of terahertz pulses generated from WSe₂/Si, Si, and monolayer WSe₂ upon excitation with different pump photon energies; (c) schematic illustration of the depletion field-accelerated charge transfer

Fig. 13. Polaron terahertz radiation in FAPbI₃^[125]. (a) Terahertz radiation induced by femtosecond laser in FAPbI₃; (b) the process of non-equilibrium photocurrent coupling with the lattice anharmonic vibration to radiate terahertz waves at corresponding frequencies (P1 and P2 are the emission modes of the polaron); (c) the sub-band structure of FAPbI₃; (d) wavelength-dependent change in coupled radiation intensity