Generation of conventional and reflective photonic nanojets and improving intensity enhancement with their superposition

Herein, we report the theoretical investigation on photonic nanojets (PNJs) of substrate-supported single-spherical dielectric microparticles. Conventional and reflective PNJs (CPNJs and RPNJs) are observed in the case of metal and dielectric substrates. The dependence of the maximum electric field intensity enhancement (η_max) of the CPNJs and RPNJs on the nanogap between the metal substrate and dielectric microsphere, the metal substrate's refractive indices, and the incident light's wavelength is studied. More importantly, the spatial separation between the CPNJs and RPNJs is found to be strongly dependent upon the angle of incidence (θ). A significant improvement in the EFIE is observed for the grazing incidence upon the superposition of CPNJ and RPNJ. The theoretical investigation is also performed by replacing the metal substrate with a dielectric substrate, and the results obtained are reported here for comparison. Finally, this investigation is extended for the dielectric microsphere placed on a thin metal film deposited on a dielectric substrate and studied the role of θ on the characteristic parameters of the CPNJs and RPNJs.