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We describe a simple terahertz (THz) time domain spectrometer with a bandwidth extending up to 7.5 THz. We show that by keeping the generation and detection crystals close to each other a high signal-to-noise ratio (SNR) can be achieved without using lock-in detection and dry nitrogen flushing. The observed spectra show very good agreement with the spectra calculated based on a simple model which includes phase matching and absorption in the generation and detection crystals. Using this set-up we have measured the absorption lines in D-tartaric acid from 0.5 THz up to 7 THz. We show that the high frequency region > 3 THz is the better choice to measure small changes in the water content of a hygroscopic sample compared to the low frequency region., Imaging Science and Technology, Applied Sciences

We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples., Imaging Science and Technology, Applied Sciences

We present measurements and calculations of the terahertz (THz) electric field measured in the near field of a metal tip used in THz apertureless near-field optical microscopy (THz-ANSOM). An analytical model in which we treat the metal tip as a linear wire antenna allows us to predict almost all of the features observed in the measurements, such as the relatively slow decay of the near-field amplitude when the tip-crystal separation increases. When the tip-crystal separation is modulated, in conjunction with lock-in detection at the modulation frequency, a smaller THz spot size is observed underneath the tip. A comparison with analytical expressions shows that in this case the electric field originates predominantly from the tip apex, with negligible contributions from the tip shaft. In the unmodulated case, the observed signal is the spatial integral of the electrooptic (EO) effect over the interaction length between the THz near field and the probe laser pulse. In the modulated case, to a good approximation, we find that the signal is proportional to the value of the THz near field at the surface of the EO crystal only., Imaging Science and Technology, Applied Sciences

A novel method developed to increase the temporal resolution of x-ray streak cameras is described. The method is analogous to the time-correlated single-photon-counting technique, which is commonly used in atomic physics. By use of short-pulse x-ray radiation from a laser-produced plasma, generated by an ultrafast laser, it is shown that a standard x-ray streak camera with a nominal temporal resolution of \>5ps can yield a temporal response of 1.6 ps. The readout technique also removes temporal jitter with respect to the triggering laser. Capabilities and limitations of the technology are discussed.