Superenhanced three-dimensional confinement of light by compound metal-dielectric microspheres

Abstract

Dielectric microspheres are capable of confining light in a three dimensional region of sub-wavelength dimensions in appropriate illuminating conditions. A compound set of metal-dielectric microspheres permitting light confined in an effective volume as small as 0.095 (λ/n)3 is shown, together with a strong focusing effect when the spheres are illuminated by focused radially polarized beams. This strong confinement arises from the surface plasmon hotspots on the rear side of the metallic microsphere induced by the so called photonic nanojets of the dielectric microsphere, and the compound set has been optimized to achieve the best result. Full width at half maximum (FWHM) could be optimized to 73nm (~0.11λ) in axial direction and 146nm (~0.23λ) in transversal direction separately. The beam shaped in that way is suitable for applications requiring small effective volume and/or strong peak intensities.