Investigation of Plasmonic Lens with Annular Structure for Laser Light Focusing

In this paper, a plasmonic lens with a continuous relief in thin metal film illuminated by a radially polarized Gaussian beam with a wavelength λ = 633 nm was studied by the finite difference time domain method. During the study, the influence of the lens geometry and material on light focusing was analyzed. It is shown that the plasmonic lens with a central depression of 90 nm depth and 1.5 μm in diameter and with the circular diaphragm of 5 μm in diameter and 500 nm in width in the silver film with a thickness of 100 nm focuses laser light into a spot with FWHM = 0.37λ and Imax = 4.127 a.u.

1. Introduction

The rapid development of fabrication technology induces new research in nanophotonics [1] and plasmonics [2] which have a lot of applications in different other areas such as microscopy [3, 4], lithography [5 –7], holography [8, 9], sensorics [10 –12], biomedicine [13 –15], and optical computing [16, 17]. Plasmonics considers the interaction between light and free electrons in conductors, for example, metals. Free electrons are excited by electric field oscillations with a frequency close to the frequency of acting electromagnetic waves. These phenomena are called plasmons [2, 18, 19].