Highly efficient broadband ultrafast plasmonics.

To date, considerable experimental and theoretical focus has been placed on the spatial control of Surface Plasmon Polaritons (SPPs) using nanostructured surfaces; however, research aimed toward accessing the ultrafast dynamics of SPPs remains vastly unexplored. Despite this, SPPs have the potential to exhibit some of the fastest possible optical processes, while maintaining the advantage of nanoscale spatial manipulation. Here, we present an experimental and computational investigation of a system that provides access to the efficient excitation of broadband, propagating SPP modes. To achieve this, a surface array of tailor designed, reduced symmetry nanostructures has been fabricated to enable the required control of the plasmon dispersion map to match sub 20 fs pulses in the near infra-red. Using a combination of optical spectroscopy and frequency resolved optical gating techniques, complimented by finite element computational analysis, the efficient excitation of propagating broadband plasmonic modes is demonstrated.

Highly ordered Fe-Au heterostructured nanorod arrays and their exceptional near-infrared plasmonic signature.

The potential of highly ordered array nanostructures in sensing applications is well recognized, particularly with the ability to define the structural composition and arrangement of the individual nanorods accurately. The use of heterogeneous nanostructures generates an additional degree of freedom, which can be used to tailor the optical response of such arrays. In this article, we report on the fabrication and characterization of well-defined Fe-Au bisegmented nanorod arrays in a repeating hexagonal arrangement. Through an asymmetric etching method, free-standing Fe-Au nanorod arrays on a gold-coated substrate were produced with an inter-rod spacing of 26 nm. This separation distance renders the array capable of sustaining resonant electromagnetic wave coupling between individual rods. Owing to this coupling, the subwavelength arrangement, and the structural heterogeneity, the nanorod arrays exhibit unique plasmonic responses in the near-infrared (NIR) range. Enhanced sensitivity in this spectral region has not been identified for gold-only nanorods of equivalent dimensions. The NIR response offers confirmation of the potential of these highly ordered, high-density arrays for biomedical relevant applications, such as subcutaneous spectroscopy and biosensing.

Magnetic-plasmonic dual modulated FePt-Au ternary heterostructured nanorods as a promising nano-bioprobe.

Ternary FePt-Au nanorods are synthesized as magnetic-plasmonic 1D nanostructures. Besides their widely tunable magnetic properties, their unique plasmonic response to the illumination polarization provides a powerful tool to optically image these sub-wavelength single nanorods. These nanoparticles also show the potential as a novel nano-bioprobe based on the demonstration of simultaneous magnetic manipulation and optical imaging of single particles inside live cells.

Magnetic manipulation and optical imaging of an active plasmonic single-particle Fe-Au nanorod.

Superparamagnetic microbeads play an important role in a number of scientific and biotechnology applications including single-molecule force measurements, affinity separation, and in vivo and in vitro diagnostics. Magneto-optically active nanorods composed of single-crystalline Au and polycrystalline Fe segments were synthesized with diameters of 60 or 295 nm using templated electrodeposition. The Fe section was magnetically soft and had a saturation magnetization of approximately 200 emu/g, resulting in a 10-fold increase in magnetization relative to that iron oxide nanoparticles. The strong plasmonic response of the Au segment of the rod in both the longitudinal and transverse directions made it possible to detect the orientation of a single rod in a polarized light microscope with nanometer resolution. These nanorods provide significantly improved physical properties over iron oxide superparamagnetic beads, making it possible to simultaneously manipulate and monitor the orientation of biomolecules with well-defined forces at the nanometer scale.

Polarization selective near-field focusing on mesoscopic surface patterns with threefold symmetry measured with PEEM.

Optically active surfaces that can provide strong localization of electromagnetic fields at predefined points are desired for applications that require high spatial resolution and high sensitivity. Here, we examine the geometric influences on, and polarization dependencies of, electromagnetic near fields on the surface of an array of tailor designed, mesoscalic, silver-coated structures with threefold symmetry characteristics. For spatially resolved mapping of the electromagnetic near fields and examining the influence of polarization, we use a photoelectron emission microscope. We find that the investigated structures not only provide an increase of the near-field intensity at their boundaries, but also that the symmetry centers of the structures focus energy in a polarization dependent manner. Changing the polarization of the incident light enables the localization of near-field intensities without displacing the excitation. Hence we show that breaking of symmetry can provide controllable centers of "hot spots" for the basis of an improved design to gain more efficient surface structures.