Semiconductor saturable absorber mirrors (SESAMs) are passive elements that have beenused in tandem with lasers in the visible and infrared wavelengths to generate mode-locked pulses for applications in communication and spectroscopy. In this thesis, the simulation and characterization of terahertz saturable absorber metasurfaces and mid-IR samples embedded with quantum-cascade (QC) absorbing material are discussed. The reflectance of each design is simulated to determine expected saturation parameters and compared with analytic estimates. The characterization of the saturable absorber involves focusing a QC-vertical external cavity surface emitting laser (VECSEL) onto a saturable absorber in a reflectionmode spectroscopy configuration to measure the reflected power. Using a gold mirror as a reference, the reflectance is measured for frequencies near 3.4 THz at room temperature. Improvements to this experiment and a preliminary design for an external cavity incorporating a saturable absorber metasurface are proposed.