Quantum cascade lasers (QCL) are semiconductor nanostructures based on inter-subband transitions between confined states in the conduction band. They filled the lack of compact and powerful sources in the mid-infrared (MIR) and in the terahertz (THz) range. This thesis presents two studies on these lasers. First part investigates resonant optical nonlinearities of QCL. We show difference frequency generation between a near-infrared (NIR) beam and the QCL THz field, i.e. at E_NIR-E_QCL. NIR excitation is resonant with interband transitions in the QCL active region, enhancing the nonlinear susceptibility of the matter. High intracavity THz field combined with the resonant NIR beam results in good efficiencies for the frequency mixing (0.13%) and in high order generation up to the third order (E_IR-3E_QCL). For the first time this nonlinear interaction is investigated within a MIR QCL. This allows demonstrating the nonlinear interaction up to 275 K, showing that the interaction is temperature independent. The second part deals with phase control of QCL emission via THz time domain spectroscopy. The novelty is the use of a Metal-Metal (MM) waveguide. These guides lead to higher temperature operations but have sub-wavelength dimensions (~10µm compared to 100µm for the emission). These dimensions make harder the coupling of a THz seed which is required to initiate the THz QCL field. "V" shape antennas are processed above QCL facets to match the impedance between free-space and guided modes. Thus, coupling efficiency and power extraction are enhanced. We demonstrate that we can phase-lock the emission of a MM QCL by THz injection seeding and resolve its amplitude and its phase.
