Fig. 1. Principle of the generating THz radiation. (a) THz radiation based on the photoconductive effect; (b) THz radiation based on the nonlinear difference frequency effect

Fig. 2. Structure of the PCA. (a) Structure of the conventional PCA; (b) PCA with integrated metal nanostructure array^[17]

Fig. 3. One-dimensional metal grating made on the DC bias electrode of PCA^[20]

Fig. 4. THz radiation formed when there is no bias voltage^[23]

Fig. 5. Performance comparison of different THz mixers. (a) Schematic diagram of the structure; (b) THz output power variation curve with frequency^[27]

Fig. 6. Schematic of the THz radiation generated when femtosecond laser irradiates a silver nanoparticle array^[33]

Fig. 7. Granular film formed when the metal thickness does not exceed the critical percolation threshold^[37]

Fig. 8. THz radiation generation when a gold split resonator ring is used. (a) Schematic diagram of the experimental device; (b) THz radiation generation under different conditions^[39]

Fig. 9. Schematic diagram of the multi-spectral resonance structure^[43]

Fig. 10. Mie resonance supported by an all-dielectric structure and its nonlinear applications. (a) Magnetic dipole supported by all-dielectric microspheres^[45]; (b) scattering efficiency under different relative permittivity when q=0.5^[45]; (c) when the pump light is incident on a single InGaAs microdisk generate enhanced double frequency signal^[48]

Fig. 11. Enhanced THz detection based on magnetic dipole resonance of all-media GaAs structure. (a) Cube-strip structure and two magnetic dipole modes; (b) schematic diagram of the enhanced THz detector; (c) cube-strip structure and electric field amplitude distribution at resonance wavelength^[50]

Fig. 12. Non-radiation mode formed by ED and TD^[46]