Partially coherent surface plasmon modes

Abstract

Elementary long-range plasmon modes are described assuming an exponential dependence of the refractive index in the neighbourhood of the interface dielectric-metal thin film. The study is performed using coupling mode theory. The interference between two longrange plasmon modes generated that way allows the synthesis of surface sinusoidal plasmon modes, which can be considered as completely coherent generalized plasmon modes. These sinusoidal plasmon modes are used for the synthesis of new partially coherent surface plasmon modes, which are obtained by means of an incoherent superposition of sinusoidal plasmon modes where the period of each one is considered as a random variable. The kinds of surface modes generated have an easily tuneable profile controlled by means of the probability density function associated to the period. We show that partially coherent plasmon modes have the remarkable property to control the length of propagation which is a notable feature respect to the completely coherent surface plasmon mode. The numerical simulation for sinusoidal, Bessel, Gaussian and Dark Hollow plasmon modes are presented.

Surface Plasmon Singularities

“…The modulus of the imaginary part given by (6) is minor, when compared with that given by (4). As a consequence the plasmon fields for a thin film propagate large distances.…”

“…The calculus details can be found in [4]. When the last expression is substituted in (3), the trajectory geometry of the electrical field on z = constant is an ellipse segment, as shown in Figure 3.…”

“…Singularities for surface plasmon fields can be obtained in a way similar to that employed for the free space case, and the corresponding surface plasmon angular spectrum model is [4,5]…”

“…where (a,b,c) are the components of a constant vector and are necessary to satisfy the boundary conditions of the electromagnetic field. More details with respect to the value of the constants can be found in [4]. The scale term τ(λ, d) is proposed to describe the coupling between the diffraction field propagating in free space and surface plasmon fields.…”

“…For optical fields in free space, the inverse process may occur, that is, when a cusped focusing region is split into two folds, vortex and bifurcation effects may occur [3]. For the case of plasmon fields, these features do not appear; however, the focusing region generates charge redistribution [4,5]. This latter property offers many interesting applications; for example, it can be implemented to polarize particles, allowing the design of plasmonic tweezers.…”