INTRODUCTION
Recently the concept of scattering-type scanning near-field
optic microscopy (s-SNOM) has been introduced and THz
microscopy with nanometre resolution has been reported [1],
[2]. In the case of s-SNOM the image formation is based on
the interaction between a very sharp probe tip and the object
whereby the resolution is no longer determined by the
wavelength but the sharpness of the tip. The method is based
on measuring the scattered near-field very close to a sample or
converting the near-field evanescent wave to a propagation
wave which can be detected in far field. The amplitude and
phase of this near field are highly dependent on the local
structure and therefore contain very high resolution spatial
information. However, extracting this information from the
scattered fields requires near-field probes capable of coupling
to the local field at a tiny point. The higher the resolution, the
more sophisticated and expensive the probes are [3].