Self-collimation of surface plasmon beams

Strong beaming of microwave surface waves with complementary split-ring-resonator arrays

A thin copper sheet, populated by an array of complementary split ring resonators, presents strong surface wave beaming in orthogonal directions at two distinct frequencies. This simple array is significantly thinner than existing single frequency beaming surfaces. The observed beaming frequencies are associated with the two lowest resonance modes of the split rings, and the beams are subwavelength in width and approximately non-diverging. The beaming is analysed through comparison of near-field scans of the surface-normal electric fields with numerical simulations.

Broadband self-collimating phenomenon in a low-loss hybrid plasmonic photonic crystal

A 2D planar self-collimating photonic crystal, based on a dielectric square lattice and a hexagonal lattice, is proposed. We demonstrate that the proposed structure can support the propagation of a hybrid surface plasmon polarition (SPP) mode with a loss of -0.017  dB/μm, and the mode size is only 0.33 μm. The defined figure of merit is one order of magnitude higher than that of the dielectric-metal structure. In addition, the self-collimating angle of more than 10° can be tuned with a silica index change of 0.08. The proposed structure possesses broad operation bandwidth of 88 nm and 58 nm for a dielectric square lattice and a hexagonal lattice, respectively. These two kinds of photonic crystals promise potential applications in photonic modulators and SPP photonic devices.

Surface plasmon polariton beams from an electrically excited plasmonic crystal

Surface plasmon polariton (SPP) beams with an in-plane angular spread of 8° are produced by electrically exciting a 2D plasmonic crystal using a scanning tunneling microscope (STM). The plasmonic crystal consists of a gold nanoparticle (NP) array on a thin gold film on a glass substrate and it is the inelastic tunnel electrons (IET) from the STM that provide a localized and spectrally broadband SPP source. Surface waves on the gold film are shown to be essential for the coupling of the local, electrical excitation to the extended NP array, thus leading to the creation of SPP beams. A simple model of the scattering of SPPs by the array is used to explain the origin and direction of the generated SPP beams under certain conditions. In order to take into account the broadband spectrum of the source, calculations realized using finite-difference time-domain (FDTD) methods are obtained, showing that bandgaps for SPP propagation exist for certain wavelengths and indicating how changing the pitch of the NP array may enhance the SPP beaming effect.

Experimental solution for scattered imaging of the interference of plasmonic and photonic mode waves launched by metal nano-slits

Using an L-shaped metal nanoslit to generate waves of the pure photonic and plasmonic modes simultaneously, we perform an experimental solution for the scattered imaging of the interference of the two waves. From the fringe data of interference, the amplitudes and the wavevector components of the two waves are obtained. The initial phases of the two waves are obtained from the phase map reconstructed with the interference of the scattered image and the reference wave in the interferometer. The difference in the wavevector components gives rise to an additional phase delay. We introduce the scattering theory under Kirchhoff's approximation to metal slit regime and explain the wavevector difference reasonably. The solution of the quantities is a comprehensive reflection of excitation, scattering and interference of the two waves. By decomposing the polarized incident field with respect to the slit element, the scattered image produced by slit of arbitrary shape can be solved with the nanoscale Huygens-Fresnel principle. This is demonstrated by the experimental intensity pattern and phase map produced by a ring-slit and its consistency with the calculated results.

Propagation of spoof surface plasmon on metallic square lattice: bending and splitting of self-collimated beams

The propagation characteristics of spoof surface plasmon modes are studied in both real and reciprocal spaces. From the metallic square lattice, we obtain constant frequency contours by directly measuring electric fields in the microwave frequency regime. The anisotropy of the measured constant frequency contour supports the presence of the negative refraction and the self-collimation which are confirmed from measured electric fields. Additionally, we demonstrate the spoof surface plasmon beam splitter in which the splitting ratio of the self-collimated beam is controlled by varying the height of rods.

Launching plasmonic Bloch waves with excited dye molecules

In this paper, we will demonstrate that excited dye molecules can be used to launch the plasmonic Bloch waves (PBWs) propagating at multi-metal-dielectric interfaces. The properties of the PBWs, such as wavevectors, propagating bands, the interface and grating period effect, were characterized by a leakage radiation microscope. Theoretical simulations were also carried out to reveal the properties of the PBWs and were consistent with the experimental results. What is more, experimental results reveal an interesting phenomenon: the PBWs launched by the excited dye molecules present different optical behaviors from those launched by far-field laser beams through attenuated total reflection. The mechanism of this difference was analyzed based on the energy conversion between the optical near-field and far-field. Our work provides a new way to launch the PBWs. Further, the coupling between the dye molecules and PBWs also demonstrates a new method to manipulate the fluorescence emission from random to controllable.