Light scattering from silicon nitride microdisks

High intensity sub-wavelength spots and low divergence nanojets are observed in a system of Si₃N₄ microdisks illuminated from the side with laser light of wavelengths 532 nm and 633 nm. The disks are of height 400 nm with diameters ranging from 1μm to 10 μm. Light scattered from the disk and substrate is observed by imaging from above. In free space light is focused inside the disks and a sub wavelength spot is observed, whereas in water the refractive index contrast is such that photonic nanojets are formed. The angular distribution of the intensity compares well to the analytical solution for the case of an infinite cylinder. The diameter dependence of the scattering is explored and matches well with theory.