Terahertz (THz) technology is revolutionizing non-destructive testing, enabling safer and more efficient quality control in industrial production. Unlike X-rays, THz radiation is non-ionizing, making it ideal for inspecting products throughout the production chain. However, THz technology remains underutilized due to limited detection methods. In this dissertation, nonlinear upconversion is used to transfer the THz measurement information to the optical range, facilitating easier and more cost-effective detection. A novel setup for the nonlinear detection of THz radiation using picosecond pulsed optical and THz radiation is presented, which utilizes different nonlinear optical media for upconversion of THz radiation, achieving a high dynamic range and signal-to-noise ratio. The initial setup enables THz time-of-flight measurements and has been tested on materials like printing paper and silicon wafers. Further enhancements allow phase measurements and reduce data acquisition time, with applications demonstrated in spectroscopy and thickness measurement. The resulting system shows a competitive alternative to established THz measurement methods. weiterlesen