Theoretical aspects of the extreme focusing of the optical field to a spatial zone of the subwavelength size are considered in the case of using isolated spherical nanometer-sized particles for this purpose. The intensity of the optical field near the surface of nanospheres of some metals in environments with different values of the refractive index under the exposure to laser radiation in a wide spectral range is calculated numerically. It is shown that as the particle radius decreases, the relative intensity of the optical field of surface plasmons increases and the zone of field nanofocusing shortens. The obtained data are compared with the calculations for gold and aluminum nanoparticles in water. Numerical results illustrating the influence of the shell thickness of composite nanoparticles (dielectric nucleus and metal shell) on the intensity of the optical field of plasmon modes are obtained. The problem of local optical foci of a transparent microparticle or the so-called photonic nanojets is considered. It is found that varying the size of a micron particle, its optical properties, and laser radiation parameters, it is possible to control efficiently the amplitude and spatial characteristics of the photonic nanojet zone.
surface plasmon, metallic nanoparticles, subdifraction focusing, photonic nanojets