Terahertz-Bildgebung mit demodulierendem Detektorarray

This dissertation is about imaging in the domain of terahertz-frequencies which is located between radio waves and light in the electromagnetic spectrum. Electrooptic detection is especially convenient to cover a wide spectrum (approximately 4 octaves) while at the same time enabling for parallel measurements at many points. Using a detector crystal, the spectral and spatial information in the terahertz beam is being transferred to the (optical) laser beam and then converted into an intensity modulation. At this point the PMD-Camera (Photonic Mixing Device) is used as a demodulating sensor array to seperate the resulting very small intensity modulation successfully from the unwanted huge background. It determines laterally resolved the amplitude of the intensity modulation, from which the electrical field magnitude of the terahertz pulse in the crystal at a sub-picosecond instant of time can be derived. While scanning in time domain the whole THz pulse can be reconstructed for 3072 different pixels in parallel enabling imaging with sub-picosecond resolution in time domain and in the region of THz frequencies. Two different imaging setups using this scheme were realized and exhaustively characterized. Exemplary measurements show that multipixel terahertz imaging now is possible without the need for an amplified pulse laser system and they illustrate the achieved optimization.