Single and Dual Photonic Jets and Corresponding Backscattering Enhancement With Tipped Waveguides: Direct Observation at Microwave Frequencies

This paper reports experiments on single and dual electromagnetic jets (also called photonic jets) emerging from a weakly multimode waveguide excited by a plane wave in the microwaves frequencies (30 GHz), ended with a tip with a special shape. The measurements are performed with a two-dimensional spatial field mapping system. This system acquires the electric field distribution at the end of the tipped waveguide. Qualitatively, the electric field maps confirm the presence of photonic jets that were recently predicted by a computational model based on boundary integral equations. Backscattering induced by the interaction of a particle with the electromagnetic jet is also measured; particles with a size smaller than the incident wavelength can be easily detected. The high sensitivity feature of the backscattering can be used to develop a near-field technique for microwave or optical imaging.