the dielectric function in metals.

Recently, dielectric nanostructures from high-index materials have proven to offer a promising alternative platform with far lower losses. [@kuznetsov_optically_2016] Like in plasmonics, it is possible to tune optical resonances from the near ultra-violet to the near infrared, yet with almost no dissipative losses. At these resonances, which can be of both electric or magnetic nature, strong local field enhancements [@bakker_magnetic_2015] and intense scattering [@kuznetsov_magnetic_2012] occur, tunable via the material and the geometry of the nanostructure. Prominent dielectric materials are, among others, silicon, germanium or III-V compound semiconductors with indirect band-gap. [@kallel_tunable_2012; @albella_electric_2014] Conventional geometries include spherical nanoparticles [@kuznetsov_magnetic_2012] or nanowires (NWs), [@cao_tuning_2010; @ee_shape-dependent_2015] but also more complex dielectric nanostructures [@wiecha_evolutionary_2017]. Dielectric optical antennas are promising candidates for applications in field-enhanced spectroscopy, [@gerard_strong_2008; @wells_silicon_2012; @regmi_all-dielectric_2016; @cambiasso_bridging_2017] imaging, [@kallel_photoluminescence_2013] to enhance and control nonlinear effects [@shcherbakov_enhanced_2014; @wiecha_enhanced_2015; @wiecha_origin_2016] or to increase the efficiency in photovoltaics [@brongersma_light_2014].

A peculiarity of dielectric particles is the possibility to simultaneously obtain a strong electric and magnetic response using very simple geometries. [@kuznetsov_magnetic_2012; @bakker_magnetic_2015; @mirzaei_electric_2015; @valuckas_direct_2017] Recently, it has been independently shown by two research groups,[@person_demonstration_2013; @fu_directional_2013] that exclusive forward (FW) or backward (BW) scattering, predicted by Kerker *et al.* in 1983 