Propagating Surface Plasmon Waves Research Articles

Azimuthal Scanning Excitation Surface Plasmon Resonance Holographic Microscopy

AbstractSurface plasmon resonance (SPR) holographic microscopy exploits surface plasmon wave as illumination and acquires both SPR intensity and phase images. It detects extremely tiny variations of weakly interacting objects owing to high sensitivity and has been applied in cell biology, material science, surface chemistry, etc. However, it is very challenging to solve the problem of poor spatial resolution due to the transverse propagation of surface plasmon wave. In this paper, an azimuthal scanning excitation method is proposed in SPR holographic microscopy to improve the spatial resolution by engineering the Fourier spectra of SPR images from dual‐arc to circular shape. The study modulates the light field with spatial position, wavevector, and polarization to realize azimuthal scanning excitation of SPR. Systematic experiments of dielectric spheres, nanowires, two‐dimension materials, and complex nanostructure are conducted to show the resolution improvement with one order of magnitude, the higher detection sensitivity of SPR phase than that of SPR intensity, and the necessities of both of high‐resolution SPR intensity and phase images to retrieve sample information in certain scenarios. Benefiting from the high detection sensitivity and spatial resolution, the proposed microscopy will find wide applications in nanoparticle analysis, low‐dimensional material characterization, and imaging extremely thin or transparent samples.

Digital plasmonic holography with iterative phase retrieval for sensing.

Propagating surface plasmon waves have been used for many applications including imaging and sensing. However, direct in-plane imaging of micro-objects with surface plasmon waves suffers from the lack of simple, two-dimensional lenses, mirrors, and other optical elements. In this paper, we apply lensless digital holographic techniques and leakage radiation microscopy to achieve in-plane surface imaging with propagating surface plasmon waves. As plasmons propagate in two-dimensions and scatter from various objects, a hologram is formed over the surface. Iterative phase retrieval techniques applied to this hologram remove twin image interference for high-resolution in-plane imaging and enable further applications in real-time plasmonic phase sensing.

Propagation of Surface Plasmon Waves along Multi Wall Carbon Nanotube with Gold Core

We have studied the propagation of surface plasmon waves along multiwalled carbon nanotube with gold core. We have modeled the shells of multiwalled carbon nanotube as impedance sheets with axially directed surface conductivity incorporating inter shell coupling in an integral equation approach. We have found that in low frequency regime optical interband transitions did not occur and guided waves propagated with low attenuation in an multiwalled carbon nanotube which has metallic shells. In the same frequency range the axial polarizability of a finite length multiwalled carbon nanotube has a resonant behavior due the antenna length matching effect. The shells with surface conductivity due to interband transitions suppressed guided wave propagation. Surface Plasmon wave propagation in a multiwalled carbon nanotube with gold core showed that in the near infrared and visible regime the shells behaved as lossy dielectric materials and suppressed surface wave propagation along the gold core. The electromagnetic characteristics of carbon nanotube based antennas have been examined in different frequency regime ranging from the microwave to the visible regime. Carbon nanotube has been demonstrated to play a crucial role connected electrically to planner periodic structures of single wall carbon nanotubes, carbon nanotube bundles and carbon nanotube arrays. The inter shells interaction leaded to inter shell electron tunneling or hopping. Fermi momentum of two incommensurable shells do not coincide within the first Brillouin zone and the inter shell tunneling vanished. In the presence of localized defects inter shell conduction increased and defectfree shells were managed by neglecting intershell conduction. We have used microscopic model for multiwalled carbon nanotube and radiation characteristics were determined by its waveguiding properties, the dispersion equation for guided wave propagation on an infinitely long multiwall carbon nanotube. We have found that the guided wave has strong retardation and high attenuation so that the frequency of a geometric resonance is not connected to the free space wave length but to a shorter effective wavelength that depends on the material properties. The obtained results were compared with the previously obtained results and were found in good agreement.

Surface plasmon wave propagation length measurement at a telecom wavelength

In this paper we present the measurements and comparison of surface plasmon wave (SPP) propagation length at the practically important telecom wavelength (1560 nm) as well as in the near infrared and visible spectral ranges. The measurements were carried out for plane SPP waves excited on Ag film surface using optical microscopy of SPP waves in the far field. We also demonstrate the possibility of visualization of a SPP waves propagation using multiphoton induced photoluminescence in silver.

Generation of optical chirality patterns with plane waves, evanescent waves and surface plasmon waves.

We systematically investigate the generation of optical chirality patterns by applying the superposition of two waves in three scenarios, namely free-space plane waves, evanescent waves of totally reflected light at dielectric interface and propagating surface plasmon waves on a metallic surface. In each scenario, the general analytical solution of the optical chirality pattern is derived for different polarization states and propagating directions of the two waves. The analytical solutions are verified by numerical simulations. Spatially structured optical chirality patterns can be generated in all scenarios if the incident polarization states and propagation directions are correctly chosen. Optical chirality enhancement can be obtained from the constructive interference of free-space circularly polarized light or enhanced evanescent waves of totally reflected light. Surface plasmon waves do not provide enhanced optical chirality unless the near-field intensity enhancement is sufficiently high. The structured optical chirality patterns may find applications in chirality sorting, chiral imaging and circular dichroism spectroscopy.

Localization of Surface Plasmon Waves in Hybrid Photodetectors with Subwavelength Metallic Arrays

The spectral characteristics of the hole photocurrent in plasmon photodetectors based on Ge/Si heterostructures with Ge quantum dots combined with regular arrays of subwavelength apertures of various shapes in a gold film on the semiconductor surface are investigated. Dispersion relations characterizing the propagation of surface plasmon waves along the metal–semiconductor interface are determined from the dependences of the photocurrent on the angle of incidence of light. It is established that the plasmonic enhancement of the photocurrent in rectangular aperture array is suppressed as compared to that in circular and square aperture arrays. It is found that, in hybrid structures with rectangular apertures, there exists a range of wave vectors where the energy of surface plasmons is independent of the wave vector of incident radiation. The results are explained by the excitation of dipole modes localized at rectangular apertures with a large aspect ratio by light waves.

Nanomechanical Plasmonic Switch Based on Multimode Interference

We propose and investigate a $2\times2$ optical switch based on multimode interference in Au-Air-Au gap plasmonic waveguide. The propagation of surface plasmon wave in gap plasmonic waveguide could be tuned by changing the size of air gap through a nanomechanical actuator. By tailoring the dispersion of the gap plasmonic waveguide, the multimode region only supports two lowest order modes with the opposite field symmetry. Switching between two states of gap size in the multimode region, the phase difference of two modes at output port could be tuned from 0 to $\pi $ leading to switching plasmonic wave energy between two output ports. The proposed structure is simple in design and compact in size, which may find promising applications in active plasmonic devices.

Mapping of surface plasmon dispersion in thin Ag–Au layered composite films

Propagating surface plasmon polaritons (SPPs) at metal–dielectric interfaces allow extreme light confinement enabling important technologies such as label-free real-time sensing and nanoscale optical wave guiding. In this work, we experimentally and theoretically map the surface plasmon dispersion of thin films of sequentially deposited silver and gold based on the Kretschmann–Raether configuration using spectroscopic ellipsometry. The results show efficient excitation of SPP modes related to the symmetric and antisymmetric modes of an insulator–metal–insulator waveguide. Since the symmetric modes have a larger electric field inside the bimetallic layer than the antisymmetric modes, we show that the dispersion for both modes can be tuned independently by controlling the thickness ratio and deposition order of metals in the film. This behavior is fundamentally different than modes in a single film or a thin film alloy. Results are in agreement with the analytical eigenmode dispersion of these modes and with a full transfer matrix model. Our results provide a complete understanding of surface plasmon modes in thin bilayer or multilayer metallic films and their ability to influence the propagation of surface plasmon waves.

Dipole-induced localized plasmon modes and resonant surface plasmon scattering

A metal film supports the continuum of propagating surface plasmon waves. The interaction of these waves with a dipole (nanoparticle) positioned some distance from the surface of the film can produce well defined localized plasmon modes whose frequency nonetheless resides inside the continuum. This leads to the resonant enhancement of scattering of surface plasmons off the dipole. The maximum of scattering is found to occur when the distance from the dipole to the surface of the film is equal to one half of the film thickness. The possibility of controllable plasmon scattering could be advantageous for the field of nanoplasmonics.

Focusing Characteristics of a Spiral Plasmonic Lens

A plasmonic lens (PL) is one of the promising photonic devices utilizing the surface plasmon wave. The surface plasmon wave can be focused using a PL structure consisting of only a single annular subwavelength slit milled into a metal film on a glass substrate. Recently, we have evaluated the beam focusing characteristics of a PL for 532 nm wavelength, which consists of a circular slit aperture of 4 µm diameter, using near-field scanning optical microscopy (NSOM), and confirmed that subwavelength focusing was attained at the center axis of the PL in both the near-field and far-field regions. However, for a PL with a circular slit, finite-difference time-domain (FDTD) simulations show that the focusing of the surface plasmon induced electric field into a single solid spot at the center cannot be achieved using circularly or linearly polarized light owing to the destructive interference between counter propagating surface plasmon waves from opposite circle slit points. In this study, we designed and fabricated a new PL with a spiral slit for 405 nm wavelength to produce a single solid focal spot due to the constructive interference at the nominal center of the PL. We measured the focusing characteristics of the PL and attained a tightly focused beam with a subwavelength spot size (∼330 nm) at 3.5 µm above the PL surface.

Investigation of the near field distribution in circular nanostructures using Stokes polarization states

In this paper, the near field distribution patterns formed from nanostripe corral and half spiral are investigated. Various near field distribution patterns are generated owning to the interference of propagating surface plasmon waves that emerged from the nanoslits or nanostripe. The half spiral nanoslits are illuminated with Stokes polarizations. Each polarization state shows a different field pattern at different locations on the surface of metal film. This is due to the excitation of surface plasmon waves at different parts of the nanostructures when illuminated with different types of polarization states. The same Stokes polarization states are also illuminated on a nanostripe corral structure. In this case, dipolar field distributions are observed when illuminated with different linear polarization states, while optical vortices are observed for circular polarization. It is believed that these interesting field patterns due to different arrangements of nanostructures could be used for near field imaging and polarization sensing.

Surface plasmon wave propagation along single metal wire

Recently, the single metal wire (SW) has become attractive for its potential applications in the terahertz and higher frequency range. However, as the most simple and typical surface plasmon polariton (SPP) transmission line, its study seems far from enough. Many important transmission behaviours have not been explained satisfactorily from the viewpoint of physics. In this paper, making use of the modified Drude model (MDM) based on the Sommerfeld theory, the transmission behaviours of SPPs along SW are systemically investigated theoretically. Some important physical phenomena such as the mode transformation, the lifetime of the radiative mode and the resonance frequency are revealed, and their mechanisms are explored. The results obtained in the paper will facilitate a general understanding of the features and the physical essence of the SPP transmission, not only for SW itself but also for other SPP transmission lines.

Nanostructure-Mediated Launching and Detection of 2D Surface Plasmons

Au nanoparticles deposited on a metallic film act as nanoantenna receivers and transmitters for the coupling of free-space radiation into, and out of, 2D surface plasmons. Nanosteps, sub-10-nm gaps between metallic films of differing thickness, can also launch and detect surface plasmons. Here we use both types of structures to locally launch propagating surface plasmon waves and probe their properties. Nanoparticle-launched surface plasmons emerge as two lobes of nominally 90 degree angular width, propagating along the direction of incident polarization. Alternatively, plasmons can be launched unidirectionally, by asymmetric illumination of a nanoparticle receiver.

Theory of Carbon Nanotubes as Optical Nano Waveguides

The propagation of surface plasmon waves in metallic single-walled carbon nanotubes is analyzed within the frame-work of the classical electrodynamics. The conduction electrons of the system are modelled by an in?nitesimally thin layer of free-electron gas which is described by means of the semiclassical kinetic theory of the electron dynamics. The effects of the energy band structure is taken into account and a more accurate dispersion relation for surface plasmon oscillations in the zig-zag and armchair nanotubes of metallic character is obtained.

Theory of multiwall carbon nanotubes as waveguides and antennas in the infrared and the visible regimes

The propagation of azimuthally symmetric guided waves in multiwalled carbon nanotubes (MWCNTs) was analyzed theoretically in the midinfrared and the visible regimes. The MWCNTs were modeled as ensembles of concentric, cylindrical, conducting shells. The influence of intershell electron tunneling on the optical properties of MWCNTs was examined by focusing on a double-walled carbon nanotube (DWCNT). Longitudinal electrostatic waves exist in DWCNTs due to intershell tunneling. Conditions for weak influence of intershell tunneling in DWCNTs were identified, and an integral-equation approach for scattering by an MWCNT was formulated when those conditions prevail. Slightly attenuated guided waves and antenna resonances due to the edge effect exist for not-too-thick MWCNTs in the far-infrared and the midinfrared regimes. Interband transitions retard the propagation of guided waves and have a deleterious effect on the performance of a finite-length MWCNT as a nanoantenna. Propagation of surface-plasmon waves along an MWCNT with a gold core was also analyzed. In the near-infrared and the visible regimes, the shells behave effectively as lossy dielectrics to suppress surface-plasmon-wave propagation along the gold core.

Sub-micron resolution surface plasmon resonance imaging enabled by nanohole arrays with surrounding Bragg mirrors for enhanced sensitivity and isolation

We present nanohole arrays in thin gold films as sub-micron resolution surface plasmon resonance (SPR) imaging pixels in a microarray format. With SPR imaging, the resolution is not limited by diffraction, but by the propagation of surface plasmon waves to adjacent sensing areas, or nanohole arrays, causing unwanted interference. For ultimate scalability, several issues need to be addressed, including: (1) as several nanohole arrays are brought close to each other, surface plasmon interference introduces large sources of error; and (2) as the size of the nanohole array is reduced, i.e. fewer holes, detection sensitivity suffers. To address these scalability issues, we surround each biosensing pixel (a 3-by-3 nanohole array) with plasmonic Bragg mirrors, blocking interference between adjacent SPR sensing pixels for high-density packing, while maintaining the sensitivity of a 50 x larger footprint pixel (a 16-by-16 nanohole array). We measure real-time, label-free streptavidin-biotin binding kinetics with a microarray of 600 sub-micron biosensing pixels at a packing density of more than 10(7) per cm(2).

Propagation of surface plasmons on Ag and Cu extended one-dimensional arrays on silicon substrates

Propagating surface plasmon waves can be supported by Cu and Ag periodic array, or grating, structures on silicon substrates. The plasmon dispersion characteristics, such as group velocity and bandgap associated with these structures are measured experimentally. In the infrared region of the spectrum (1.3–1.6μm) the properties of surface plasmons supported by these Ag and Cu periodic structures are virtually indistinguishable. The plasmon dispersion can be modified by varying either the grating period or the plasmon order. The plasmonic bandgap for this array geometry increases with increasing plasmon order.

Electromagnetic response of a point-dipole crystal

We study the electromagnetic response of a cubic array of polarizable and resonant point dipoles. We show, that in addition to the formation of photonic and polaritonic bands and gaps in the dispersion of transverse waves, the array allows for bulk and surface plasmon wave propagation, as well as negative refraction in a polaritonic band, and subwavelength lensing. We suggest experimental arrangements for demonstration of these effects, both at microwave and optical frequencies.

Scattering from metallic and dielectric rough surfaces

Using a generalization of the integral theory of metallic and dielectric gratings developed in our laboratory 15 years ago, we propose a rigorous integral theory of scattering by metallic or dielectric nonperiodic rough surfaces leading to a single integral equation. The numerical implementation has been carried out despite strong difficulties for TM polarization and metallic surfaces because of propagation of surface plasmon waves outside the illuminated region of the rough surface. Numerical results show the influence of the statistical parameters of the asperities on the absorption phenomena for metallic surfaces. Then the influence of asperities on the total transmission around Brewster incidence is studied. Finally numerical results of enhanced backscattering from perfectly conducting, metallic, and dielectric random rough surfaces are given.