Abstract
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 488 nm, 532 nm and 633 nm. The disks are of height 400 nm with diameters ranging from 1μm to 10μm. 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. Two distinct cases of scattering pattern are observed with even and odd numbers of lobes. Finally when the disks are illuminated with a focused Gaussian beam perpendicular to the substrate an extremely low divergence beam is observed. This beam has a divergence angle over 10 times smaller than a focused Gaussian in free space with the same waist.
Highlights
Scattering of light by spherical and cylindrical particles has been of interest for over 100 years since the popular derivation of the analytical solution for a sphere by Mie in 1908 [1]
Light scattering from an object depends on its size relative to the incident wavelength, characterized by the size parameter xs = 2π R / λ, and the ratio of the refractive index of the object to the surrounding medium, known as the refractive index contrast (m)
For a refractive index contrast of 2.1, (Si3N4 in air) incident light is focused to a subwavelength spot which is located just inside the opposite surface of the disk
Summary
Scattering of light by spherical and cylindrical particles has been of interest for over 100 years since the popular derivation of the analytical solution for a sphere by Mie in 1908 [1]. Light scattering from an object depends on its size relative to the incident wavelength, characterized by the size parameter xs = 2π R / λ , and the ratio of the refractive index of the object to the surrounding medium, known as the refractive index contrast (m). If a particle has a small size parameter (xs
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