Resolving power beyond the diffraction limit demonstrated with composed pupils at microwave and THz frequencies

In order to increase the resolving power of an optical system, the results obtained with super-gain antennas could be transferred to optics as proposed by Toraldo di Francia since 1952, with the adoption of special kinds of pupils consisting of concentric circular slits. Experimental work performed in the microwave range confirms the correctness of the theoretical predictions. In addition, experiments performed in the terahertz range give further evidence of the increased resolving power. The improvement of the resolving power results to be comparable with the maximum value predicted by the theoretical model: similar to 1.9 for the pupils under test. In both cases, the adopted pupil consists of three circular zones, with the intermediate one made of a suitable dielectric, the thickness of which is about one wavelength. Apparent contradiction with the uncertainty principle can be interpreted in the framework of the "weak measurements" theory, thus supplying an alternative interpretation.