Fig. 1. THz radiation from ferromagnetic thin film based on ultrafast demagnetization effect. Electric field intensity of THz pulse radiated from (a) Ni thin film^[11] or (b) Fe thin film^[17]; (c) schematic of THz radiation from Co₂MnSn thin film^[22]; (d) electric field intensity of THz radiation from Co₂MnSn thin film^[

Fig. 2. THz radiation from magnetic heterostructure^[12]. (a) THz wave emitted from ferromagnetic/non-ferromagnetic thin film heterostructure; (b) schematic of ISHE; (c) THz emission signals from Fe/Ru and Fe/Au when magnetization directions are opposite; (d) spectrum of THz radiation

Fig. 3. Factors influencing signal intensity of THz emission. (a) Amplitude of THz signal radiated from Co₂₀Fe₆₀B₂₀/NM and spin Hall conductivity of Co₂₀Fe₆₀B₂₀/NM versus NM material^[28]; (b) maximum THz amplitude versus thickness of Pt layer when thickness of Fe layer is 12 nm^[30]; (c) maximum THz amplitude versus thickness of Fe layer whe

Fig. 4. Strong THz wave generated from metallic heterostructure by femtosecond laser. (a) Schematic of thin-film Fabry-Pérot cavity^[28]; (b) schematic of THz emission from tri-layered film^[28]; (c) THz signal generated by tri-layered film THz emitter, photoconductive switch, ZnTe and GaP^[28]; (d) amplitude and phase spectra of polytetrafluoroethylene (PTFE

Fig. 5. THz radiation from photonic crystal structure. (a) Schematic of THz emitter with structure of metal-dielectric photonic crystal^[44]; (b) absorptivity of femtosecond laser by photonic crystal versus thickness of SiO₂ layer^[44]; (c) comparison of THz radiation signals from photonic crystal (d=110 nm, n=3) and tri-layered film structure (d

Fig. 6. THz wave radiated from magnetic heterostructure with striped pattern^[45]. When stripe orientation is (a) parallel or (b) perpendicular to orientation of magnetic field, polarization direction of THz pulse radiated by Fe/Pt striped structure; (c) optical micrograph of striped structure; THz signals in (d) time-domain and (e) frequency-domain radiated by striped structures with different θ

Fig. 7. THz radiation based on IREE effect^[51]. (a) Schematic of THz radiation; (b) THz signals in time-domain from Fe/Ag/Bi and Fe/Bi/Ag structures

Fig. 8. Speed limit test of spin Seebeck effect ^[55]. (a) Ultrafast spin current in YIG/Pt system triggered by hot electrons in metal layer; (b) THz radiation signals from YIG(3 μm)/Pt(5.5 nm) sample; (c) THz radiation signals from YIG (3 μm)/Pt(5.5 nm) and YIG(3 μm)/W(5.5 nm) samples