Near field microscopy is commonly achieved thanks to the exaltation of the field between a tip and the sample. The free space electromagnetic wave at infrared or THz frequencies is focused in this extremely small area compared to the wavelength. In many cases, the probe is a classical AFM-tip which was not designed and fabricated for this purpose. We present here an original approach in order to optimize the interaction between the impinging electromagnetic wave and the antenna-like probe. As a proof of concept we have modified with FIB (Focused Ion Beam) technique a commercial AFM-tip. The results in terms of resolution are very encouraging.