The detailed analysis of localized elongated photonic nanojets generated by a graded-index microellipsoid is reported. Using high resolution finite-difference time-domain simulation, we have studied the distribution of the electric energy density within and in the vicinity outside a dielectric core-shell microellipsoid. Here we consider dielectric composite microellipsoid consisting of a core and several concentric shells having different types of index grading. It becomes possible to elongate the nanojet abnormally. The latitudinal and longitudinal sizes of a nanojet and its peak intensity depending on the optical contrast variation of shells are numerically investigated. The results may provide a new ultra-microscopy technique for optical detection of natural or artificially introduced nanostructures deeply embedded within biological cells.
Progress In Electromagnetics Research Letters 37, pp.153-165