The Focusing Property of Immersed Plasmonic Nanolenses Under Radially Polarized Illumination

The focusing property of immersed plasmonic nanolenses was theoretically studied by a rigorous electromagnetic numerical analysis method. The immersed plasmonic nanolens consists of a through central hole surrounded by a set of concentric slits with a period of plasmonic wavelength. The computational results show that the focusing property of immersed plasmonic nanolenses is, in general, similar to that of traditional immersion lenses. Normally, for the given incident wavelength, the higher the refractive index of the immersed medium, the smaller the focusing spot. For different wavelengths, the focusing property of immersed plasmonic nanolenses shows the similar focusing property, in comparison with traditional lenses, as well. A focal length of around half of the incident wavelength and the smallest focusing spot of less than a quarter of the incident wavelength have been achieved. The physical explanation of the different focusing behavior of immersed nanolenses is also given. The reported immersed plasmonic nanolens with a quasi-far-field focal length, as well as a superfocusing spot, can find applications in areas including nanolithography, data storage, super-resolution imaging, and so on.