Construction of complex nanostructures (metasurfaces) became accessible over the past years due to variety of methods like lithography or deposition of nanoparticles. Rapid development of numerical methods for simulation of light interaction with those metasurfaces allow for design of optical elements that act as geometrical phase elements (GPE), mode filters, topological or chiral converters. We report on systematic approach in the designing of such GPE’s using engineered clusters of nanoparticles (meta-atoms) on a substrate. We study in detail optical properties of such nanoclusters and investigate how individual properties of nanoparticles are influencing the collective response of few selected GPE’s.
Gaussian beam and higher modes can be introduced by making the position of their source complex (moving it to the complex point). This concept has lead later to the introduction of so-called complex source beams. We build here upon our previous development of complex source vortices (CSV) and introduce an analytical expansion of scalar CSVs into spherical multipoles. We extend it to the vector CSVs and study in detail cases of rather complex polarisation topologies. This expansion enables us to introduce a closed-form analytical Mie theory. We apply our developments to investigate chiral planar nanostructures and optimise their optical properties.