Photonic nanojet super-resolution in immersed ordered assembly of dielectric microspheres

- Ordered microassemblies of dielectric microspheres immersed in a transparent matrix exposed to a light wave produce an array of the “photonic nanojets” coupled through the field interference.
- “Photonic nanojet” parameters depend on the inter-sphere gap and immersion depth.
- Sphere microassembly can produce the jets with the sub-diffraction spatial resolution if the particles are loosely packed and semi-immersed.

Specific spatially-localized optical field structure, which is often referred to as a photonic nanojet (PNJ), is formed in the near-field scattering area of non-absorbing dielectric micron-sized particle exposed to an optical radiation. By virtue of the finite-difference time-domain technique we numerically simulate the two-dimensional array of PNJs created by an ordered single-layer microassembly of glass microspheres immersed in a transparent polymer matrix. The behavior of the main PNJ parameters (length, diameter, and intensity) is analyzed subject to the immersion depth of the microparticles and cooperative interference effects of the neighboring microspheres. We show that depending on microassembly configuration, the PNJ quality can be significantly improved; in particular, the PNJ spatial resolution better than λ/5 can be achieved.