Starting their review from observations recorded 2,000 years ago, the authors look at the development of one of the tiniest lenses that are now able to focus light in a nanojet. Light refraction in small dielectric spheres attracted a lot of interest over time, and due to its simple geometry this problem is solved analytically. The tiny focal spot behind the sphere is elongated, and that is why it was termed a nanojet. The authors analyze various regimes of the light scattering, looking at the properties of spheres of different size having different index of refraction, and finally they show results for shapes other than spheres. They provide an overview of several proposed applications of spheres, starting from strong enhancement of light intensity to imaging applications on the nanoscale, where the resolution as small as one tenth of the wavelength was reported. The authors show various unusual and unexpected phenomena in the system and illustrate, for example, that in the focal spot created by a sphere, the magnetic field of the electromagnetic wave is enhanced more strongly than is the electric field.
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