High spatial resolution imaging is implemented with a novel collection mode near-field terahertz (THz) probe. Exceptional sensitivity of the probe allows imaging with spatial resolution of few microns using THz pulses with spectral content of 120 to 1500 microns. In the present study, the principle of the probe operation as well as the probe design and characteristics are described.
The probe performance is related to effective detection of radiation coupled into the probe aperture. Propagation of short single-cycle electromagnetic pulses through apertures as small as 1/300 of the wavelength is experimentally and numerically studied. Finite-difference time-domain method is used to model propagation of THz pulses through the probe aperture in order to optimize the probe design. It is shown that the probe sensitivity is significantly improved if the detecting antenna measures electric field coupled through the aperture in the near-field zone rather than in the far-field zone. Effects of temporal and spectral pulse shaping are described by frequency-dependent transmission at the near- or below cutoff regimes of the aperture. Imaging schemes, properties, and artifacts are considered. The technique provides the best to date spatial resolution capabilities in the THz range of the electromagnetic spectrum
