The objective of this thesis is to investigate the generation of terahertz waves in LiNbO₃ and PPLN waveguides via χ(2) processes, using a high-repetition-rate ytterbium-based laser operating at a wavelength of about 1 µm. In a LiNbO₃ waveguide with a 500 × 500 µm² cross-section, broadband THz radiation spanning 4 THz and centered at 3.1 THz was generated through polariton parametric scattering. In a PPLN waveguide of the same dimensions, narrowband THz radiation centered at 0.48 THz with a bandwidth of 180 GHz was obtained using a chirped-pulse and temporal-delay technique. As a potential application of this second approach, the selective excitation of specific spatial mode profiles in the PPLN waveguide was numerically demonstrated by solving the depleted nonlinear optical coupled-wave equations. For chirped pulses with a duration of 100 ps, a relative delay of 41.9 ps enabled efficient generation of the TE₁₀ mode, while delays of 42.0 ps and 43.9 ps selectively generated the TE₂₀ and TE₃₀ modes, respectively, with high efficiency compared to other modes.
