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Van der Valk, N.C.J. (author)Terahertz (=1012 Hz) radiation is a form of electromagnetic radiation that is at this moment used rarely for imaging purposes. However, there are indeed reasons to assume that imaging with terahertz radiation could be very useful. First, many materials, such as paper, plastics and clothing are transparent for terahertz radiation, while they...doctoral thesis 2005
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Van der Valk, N.C.J. (author), Van der Marel, W.A.M. (author), Planken, P.C.M. (author)We present a new method to measure the polarization state of a terahertz pulse by using a modified electrooptic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and...journal article 2005
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Van der Valk, N.C.J. (author), Planken, P.C.M. (author), Buijserd, A.N. (author), Bakker, H.J. (author)We present measurements on terahertz generation by optical rectification, in which both the thickness of the generation crystal and the wavelength of the generating optical pulse are varied. The difference between the group velocity at optical frequencies and the phase velocity at terahertz frequencies affects the time trace and spectrum of the...journal article 2005
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Wang, K. (author), Mittleman, D.M. (author), Van der Valk, N.C.J. (author), Planken, P.C.M. (author)We have performed measurements on terahertz (THz) apertureless near-field microscopy that show that the temporal shape of the observed near-field signals is approximately proportional to the time-integral of the incident field. Associated with this signal change is a bandwidth reduction by approximately a factor of 3 which is observed using both...journal article 2004
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Van der Valk, N.C.J. (author), Planken, P.C.M. (author)We report on a method to obtain a subwavelength resolution in terahertz time-domain imaging. In our method, a sharp copper tip is used to locally distort and concentrate the THz electric field. The distorted electric field, present mainly in the near field of the tip, is electro-optically measured in an (100) oriented GaP crystal. By raster...journal article 2002