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Measurements of spatially resolved beam profiles of single-cycle terahertz pulses are presented. In the approach here the terahertz beam is scanned over the stationary electro-optic detector using a gimbal-mounted mirror. A detailed study of the temporal- and frequency-dependent field in the region of the terahertz focus reveals field patterns which are dominated by diffraction and absorption. The observed field distribution is reproduced in model calculations. The exceptionally high signal to noise ratio and the high frequency and spatial resolution of the experiment here facilitate the observation of minute field distortions caused by the anomalous dispersion of absorbers in the beam path from the spatially resolved field pattern.

The water content in polyglycol oils is investigated by Terahertz Time-Domain Spectroscopy (THz-TDS). These oils are able to dissolve a certain percentage of water. Changes in the absorption coefficient and refractive index are observed related to the amount of water added to the pure oils. Comparison of the experimental data with predictions based on Beer-Lambert and Lorentz-Lorenz-theory, respectively, exhibits an excellent agreement. Analyses with Fourier Transform Infrared (FTIR) Spectroscopy reveal sensitivity similar to the THz-TDS experiment. THz- TDS may offer powerful tools to quantitatively determine the water concentration in petroleum products

Terahertz Time-Domain Spectroscopy (THz-TDS) is used to investigate water and soot contaminations in oils, exhibiting different dilution modes. For synthetic polyglycol oils, the water is dissolved due to the polar behavior of the oil, whereas in non polar mineral oils the water-oil compound forms an emulsion. This behavior is modeled with an effective medium approximation (EMA) formalism. Small soot agglomerates are remaining in suspension when mineral oils are polluted with soot particles. In this case, the absorption spectrum is dominated by scattering effects. Due to the small particle size of the soot agglomerates compared to the THz wavelength, coherent scattering is the dominant process.

Ein Terahertz-Time-Domain-Spektroskopie- (THz-TDS-) System mit elektrooptischem Detektor auf der Basis von ZnTe wird vorgestellt. Als Laserquelle dient ein Ti:Sa-Laser, der Laserpulse mit einer Dauer von ca. 10 fs bei einer zentralen Wellenlänge von 800 nm liefert. Durch Optimierung des Detektionsverfahrens wurde mit nur 25 mW Laserleistung ein Signal-Rausch-Verhältnis (SNR) von größer als 103 erzielt. Die aufgenommenen Spektren bekannter Substanzen weisen materialspezifische Absorptionslinien auf und erlauben deren eindeutige Erkennung.