Modelling of surface waves on a THz antenna detected by a near-field probe.

We have modelled the experimental system based on the sub-wavelength aperture probe employed in our previous work for terahertz (THz) surface plasmon wave imaging on a bowtie antenna. For the first time we demonstrate the accuracy of the proposed interpretation of the images mapped by the probe. The very good agreement between numerical and experimental results proves that the physical quantity detected by the probe is the spatial derivative of the electric field normal component. The achieved understanding of the near-field probe response allows now a correct interpretation of the images and the distribution of the electric field to be extracted. We have also carried out the first assessment of the probe invasiveness and found that the pattern of the surface plasmon wave on the antenna is not modified significantly by the proximity of the probe. This makes the experimental system an effective tool for near-field imaging of THz antennas and other metallic structures.