Arbitrary Bending Plasmonic Light Waves

Abstract

We demonstrate the generation of self-accelerating surface plasmon beams along arbitrary caustic curvatures. These plasmonic beams are excited by free-space beams through a two-dimensional binary plasmonic phase mask, which provides the missing momentum between the two beams in the direction of propagation, and sets the required phase for the plasmonic beam in the transverse direction. We examine the cases of paraxial and nonparaxial curvatures and show that this highly versatile scheme can be designed to produce arbitrary plasmonic self-accelerating beams. Several different plasmonic beams, which accelerate along polynomial and exponential trajectories, are demonstrated both numerically and experimentally, with a direct measurement of the plasmonic light intensity using a near-field-scanning-optical-microscope. PACS numbers:Surface-plasmon-polaritons (SPPs) are surface electromagnetic waves that are coupled to electron waves, which propagate at the interface between a dielectric and a metallic medium [1]. The ability to control and guide plasmonic light waves opens exciting new possibilities in photonics and electronics [2,3]. Specifically, nanoscale on-chip technologies such as surface plasmon circuitry [4], sub-wavelength optical devices [5,6] and nanoscale electro-optics [7], as well as new applications in biology and chemistry such as bio-sensing, optical trapping and micro-manipulation at the nanoscale [8] have attracted great interest in recent years.In the last several years, new types of plasmonic beams have been realized having unique properties. These beams can be "non-spreading" -i.e. preserve their spatial shape with propagation, as well as "self-accelerating" -i.e. propagate along curved trajectories. For example, the plasmonic CosineGauss beam [9] is a non-spreading beam which propagates along a straight trajectory, whereas the plasmonic Airy beam [10-13] is non-spreading and propagates along a parabolic trajectory. The latter, is the only self-accelerating plasmonic beam demonstrated until now and is restricted to a parabolic trajectory. In this paper, we address the question of whether it is possible to create self-accelerating surface plasmon beams that propagate along arbitrary curved trajectories.The Airy function is an exact solution of the paraxial Helmholtz equation, or equivalently, of the Schrodinger equation for a free particle [14] which carries infinite energy. An actual Airy beam, however, carries finite energy and is obtained by truncating the infinitely long tail of the Airy function by using an exponential or Gaussian window [15]. The truncated Airy beam preserves its shape and self-accelerates, but only over a finite distance. Recently it was shown [16,17] that free-space non-spreading beams, propagating along arbitrary convex trajectories over finite distances, can be realized. However, the question still remains whether this concept, demonstrated so far only with free-space beams, can be used for the case of surface plasmons waves. If so, several fundamental challenges, owing t...

Dual behavior of caustic optical beams facing obstacles

“…Moreover, an experimental analysis is carried out in order to support the theoretical predictions. The findings of this work can be extended to other reported caustic beams with arbitrary complex trajectories [18][19][20] and other types of selfbending and self-healing beams such as Mathieu and Weber beams [21].…”

Self-Accelerating Beams of Photons and Electrons

“…Since the wave-vector of SPPs is larger than that of free space beams, a special grating should be constructed on the surface in order to excite these beams from free-space and set their required transverse profile. Quite recently we have extended this concept of arbitrary "bending" to the field of SPP waves [6], thereby generating accelerating beams with different polynomial and exponential trajectories. Furthermore, the non-paraxial Mathieu and Weber SPP beams were also realized [7].…”

Curved Surface Plasmon Polariton Excitation With Shaped Beam by Fifth-Power Phase Mask

“…Li et al [18], [19] experimentally realized a plasmonic Airy beam by directly coupling a laser beam, the plane wave incidence and the point source with a carefully designed, nonperiodically arranged sliver nanocave array also fabricated by FIB milling. Epstein and Arie [20] excited self-accelerating plasmonic beams along several different polynomial and exponential trajectories by free-space beams through two-dimensional binary plasmonic silver phase masks fabricated by EBL. Arie et al [21] demonstrated and experimentally converted the free space laser beam to Mathieu and Weber SPP beams by the silver plasmonic holograms written also by using EBL.…”

“…Till now, there are mainly two kinds of methods to form plasmonic curved waves at metallic surface: 1) directly coupling free-space curved beams to surface plasmon polariton (SPP) through a metallic coupler [4] and 2) coupling laser beams to curved SPP with engineered nanoscale specific metallic phase masks [17]- [20]. For the first kind of method, Zhang et al [4] coupled 1-D free-space Airy beams to plasmonic Airy beams through a gold grating fabricated by electron beam lithography (EBL).…”