Ince-Gaussian beam-excited surface plasmon polaritons with Ag surface structure

Owing to the capability of achieving tighter spatial confinement and higher local field intensity, surface plasmon polaritons (SPPs) have been investigated extensively. To excite SPPs with plane wave and conventional Gaussian... [ view full abstract ]

Owing to the capability of achieving tighter spatial confinement and higher local field intensity, surface plasmon polaritons (SPPs) have been investigated extensively. To excite SPPs with plane wave and conventional Gaussian beam have been well-discussed previously. Recently, researchers have great interests in studying the properties of the SPPs that excited by structure lights, such as cogwheel-like structured light beams, optical vortex beams, and etc.. This study made subwavelength-scale Ag structure on the ITO glass with e-beam lithography, and investigated the resulting SPPs that excited by normally incident focusing Ince-Gaussian Beams (IGBs) [Opt. Express 29, 144] of several different modes. Where the IGBs is a third complete family of exact and orthogonal solutions of the paraxial wave equation. The Ag structure this study adopted is composed of two groups of thin periodic Ag bars. The wavelength of the IGB this study used is 1064 nm. Several different widths and periods of the Ag structures have been made and tested in this study. The SPPs that excited by several different IGBs have been measured by scanning near-field optical microscope (SNOM). The figure shows a measured near-field images (|E|^2) detected by SNOM, while the incident IGB is even IGB with mode number: order p=2 and degree m=2. Two yellow dotted lines in the figure indicate the boundaries of two groups of Ag bars. The distance between two boundaries (two yellow dotted lines) is 14 micrometer. In this experiment, the two bright spots of the incident IGB is just hitting on the boundaries of two groups of Ag bars. Several experimental results of this study reveal that while the edge of the IGBs hitting on both boundaries of two group of the Ag bars, the resulting SPPs propagating from the Ag bar along the metal−dielectric interface forms sable subwavelength-scale slit-like interference patterns. The phenomenon is interesting, and the relation between the slit-like interference patterns and Ag structure is worth to be further investigated. Suitable arrangements of the periodic thin Ag bar might achieve more different subwavelength-scale spatial localized interference patterns, which might be useful to nanoimaging, as well as to nanolithography and nanomanipulation.