Intensity of photonic nanojets improved by means of a mirror.

Photonic nanojets (PNJs) have been used successfully in super-resolution imaging and optical intensity enhancement benefitting from their sub-wavelength beam waists and high intensity. Herein, we introduce a method to further enhance the intensity of PNJs through adding a mirror. About 4 times enhancement factor can be achieved by appropriately selecting the gap length between the cylinder, which generates the PNJ under a TE polarized plane wave illumination, and the mirror. The intensity distributions of the PNJs can be modulated by changing the gap length. Our simulation shows that the full width at half maximum (FWHM) of the beam waist of the enhanced PNJ can reach less than λ/2n_b (n_b, the refractive index of the surrounding medium) with the illumination at 638 nm, when the refractive index of the cylinder is carefully chosen. Finally, we demonstrate that the added mirror can also work in TM and circular polarized illuminations. Our results are of interest for various applications in nanoparticle manipulation and optical nonlinear enhancement. [ABSTRACT FROM AUTHOR]