Fig. 1. Diagram of experimental setup [ femtosecond laser is focused by a cylindrical lens to excite a lithium niobate (LN) waveguide to generate terahertz waves. These terahertz waves are collected by two off-axis parabolic mirrors (OAPs) and detected by a photoconductive antenna array (PCA)]

Fig. 2. Curves of terahertz time-domain signal amplitude (E_THz) generated from 50-μm-thick lithium niobate waveguide detected by on-chip electro-optic sampling and photoconductive antenna. (a) Time-domain signal curve collected by on-chip electro-optic sampling system; (b) time-domain signal curve collected by photoconductive antenna system

Fig. 3. Far-field THz waves generated by lateral excitation of two lithium niobate waveguides with length of 10 mm and different thicknesses. (a) Time domain and (b) spectral curves of far-field THz wave generated by lateral excitation of 50 μm-thick lithium niobate waveguide with pump energy of 0.4 mJ; (c) time domain and (d) spectral curves of far-field THz generated by lateral excitation of 100 μm-thick lithium niobate waveguide with pump energy of 0.4 mJ

Fig. 4. Simulation results of terahertz wave frequency selection characteristics in lithium niobate waveguides with different thicknesses

Fig. 5. Far-field THz waves generated by lateral excitation of two lithium niobate waveguides with length of 5 mm and different thicknesses. (a) Time domain and (b) spectral curves of far-field THz generated by lateral excitation of 50 μm-thick lithium niobate waveguide with pump energy of 0.4 mJ; (c) time domain and (d) spectral curves of far-field THz wave generated by lateral excitation of 100 μm-thick lithium niobate waveguide with pump energy of 0.4 mJ

Fig. 6. Far-field THz waveforms and spectral curves of lithium niobate waveguides with thickness of 100 μm and varying lengths (0.5 m, 1 mm, 1.5 mm, and 2 mm) when laterally excited by femtosecond laser with energy of 0.4 mJ. (a)(b) 0.5 mm lithium niobate waveguide;(c)(d) 1 mm lithium niobate waveguide;(e)(f) 1.5 mm lithium niobate waveguide;(g)(h) 2 mm lithium niobate waveguide