Fig. 1. Dispersion curves of phonon polariton in LiNbO₃

Fig. 2. Cherenkov radiation in LiNbO₃ generated by femtosecond laser pulse^[34]

Fig. 3. Simulated terahertz electric field intensity distributions in LiNbO₃ crystals with different thicknesses

Fig. 4. Schematic of pump-probe process in LiNbO₃ crystal^[34]

Fig. 5. Schematic of pump-probe system of terahertz phonon polariton^[34]

Fig. 6. Moving intersection of tilted wavefront with LiNbO₃ chip at different moments. (a) Wavefront reaching chip; (b) wavefront entering chip; (c) wavefront leaving chip

Fig. 7. Schematic of phase contrast imaging

Fig. 8. Quantitative detection results by phase contrast imaging^[32]. (a) Phase-contrast image of terahertz field after excitation of 42 ps; (b) corresponding electric field signal

Fig. 9. Measurement system of self-compensating polarization gating imaging^[27]

Fig. 10. Spatio-temporal evolution of terahertz wave electric field and dispersion curves in experiments^[32]. (a) Spatio-temporal distribution of terahertz wave; (b) dispersion curves for terahertz wave propagation

Fig. 11. Dispersion curves of terahertz wave in different propagation directions^[27].(a) θ=20°; (b) θ=50°; (c) θ=70°; (d) θ=90°

Fig. 12. Effective refractive indexes of terahertz waves in LiNbO₃ chip^[27]. (a) θ=0°, effective phase refractive index; (b) θ=70°, effective phase refractive index; (c) θ=0°, effective group refractive index; (d) θ=70°, effective group refractive index

Fig. 13. Functional structures on LiNbO₃ chip. (a) Dipole antenna; (b) array of split ring resonators; (c) tilted waveguide; (d) photonic crystal

Fig. 14. Schematic of machining platform for femtosecond laser direct writing

Fig. 15. Image and dispersion curves of terahertz wave propagating in rectangular waveguide^[49].(a) Image of terahertz wave in experiment; (b) dispersion curves of line 1; (c) dispersion curves of line 2

Fig. 16. Terahertz field distributions in Fabry-Perot resonator at different time delays Δt^[36]. (a) Δt=0 ps; (b) Δt=1.6 ps; (c) Δt=5.6 ps; (d) Δt=6.4 ps; (e) Δt=6.8 ps; (f) Δt=35.8 ps

Fig. 17. Spatio-temporal evolution in Fabry-Perot resonator and its Fourier transform^[36]. (a) x-t plot; (b) x-f plot

Fig. 18. Schematic, experimental and simulated results of antennas with tips^[29]. (a) Schematic of experiment; (b) ratio of gap signal to reference value; (c) intensity distributions of terahertz fields with different frequencies in y direction

Fig. 19. Schematic of LiNbO₃ chip with surfaced metamaterial structure, spatio-temporal evolution and Fourier spectra of terahertz wave^[30]. (a) Schematic of experiment; (b) x-t plot; (c) transmitted and reflected spectra

Fig. 20. Experimental results of metasurface antenna^[31]. (a) Structural diagram; (b) spatio-temporal evolution; (c) dispersion curves