Apertureless near-field microscopy using a knife blade as a scanning probe at millimeter wavelengths

We report on the use of a knife blade as a scanning probe for apertureless near-field microscopy at millimeter wavelengths. Since the knife blade probe is a wider version of the metal tip probe commonly used in this technique, and therefore the interaction area between the probe tip and the sample is larger, an improvement in the intensity of the measured near-field signal is expected. The knife blade probe can also work as a part of a resonator in the illumination optics used in this microscopy format to enhance the strength of the near field that interacts with the sample, resulting in a further improvement in the signal intensity. A scanning method and an image reconstruction algorithm based on computerized tomography are adopted to obtain 2-D near-field images. Experiments performed at 60 GHz using a knife blade with a tip radius of 6 μm (∼ λ / 1000) show that the signal intensity is enhanced by ∼20 dB compared with an equivalent metal tip probe, and that an image resolution approaching the tip radius of the knife blade is achieved.