Surface Plasmon Polariton Absorption Research Articles

Two-level systems coupled to Graphene plasmons: A Lindblad equation approach

In this paper, we review the theory of open quantum systems and macroscopic quantum electrodynamics, providing a self-contained account of many aspects of these two theories. The former is presented in the context of a qubit coupled to a electromagnetic thermal bath, the latter is presented in the context of a quantization scheme for surface-plasmon polaritons (SPPs) in graphene based on Langevin noise currents. This includes a calculation of the dyadic Green’s function (in the electrostatic limit) for a Graphene sheet between two semi-infinite linear dielectric media, and its subsequent application to the construction of SPP creation and annihilation operators. We then bring the two fields together and discuss the entanglement of two qubits in the vicinity of a graphene sheet which supports SPPs. The two qubits communicate with each other via the emission and absorption of SPPs. We find that a Schrödinger cat state involving the two qubits can be partially protected from decoherence by taking advantage of the dissipative dynamics in graphene. A comparison is also drawn between the dynamics at zero temperature, obtained via Schrödinger’s equation, and at finite temperature, obtained using the Lindblad equation.

Surface plasmon hole burning via doppler broadening

The hole burning phenomenon is investigated in a five-level atomic configuration at the interface of cesium and gold in the presence of Doppler broadening. The group index and refractive index of surface plasmon polaritons (SPPs) becomes equal in the hole burning region, which display that the phase and group velocities of SPPs are matched. The propagation length during absorption of SPPs decreases with the decrease of absorption, while there are increases with amplification of SPPs. This study could have significant applications in optical storage devices, telecommunication, imaging, and enhancement of plasmonster memory.

Incoherent and coherent manipulation of surface plasmon hole burning

We theoretically investigate the spectral hole burning of surface plasmon polaritons (SPPs) at an interface between rubidium (87Rb) atomic medium and silver. A typical Lamb dip can be observed at a certain frequency where the absorption of SPPs is suddenly reduced. By applying Kerr-type nonlinearity to the 87Rb atomic gas, the slope of dispersion becomes more normal and steeper. Under the effect of Doppler broadening, a group index of at the SPPs hole burning region is obtained and is further enhanced to with the application of Kerr-nonlinearity. Similarly, the propagation length of SPPs is increased at the hole burning region and is further enhanced with Kerr-nonlinearity. Further, we show that this nonlinear effect results in the enhancement of the phase shift from 0.02 to 1.5 radian at the hole burning region. These results may find important applications in nano-photonics, optical tweezers, photovoltaic devices and sensing technology.

Insulator to metal transition induced by surface plasmon polaritons in VO2/Au thin films.

We report on a new mechanism capable of inducing the insulator-metal transition (IMT) in VO2 via surface plasmon polaritons (SPP). Our theoretical model predicts that for a bilayer Au-VO2 sample an enhanced electromagnetic energy density at the Au-VO2 interface will occur at 1064nm laser wavelength when SPPs are excited in the Au layer. This effect can assist the IMT in the VO2 layer and at the same time, the SPP absorption can be used to detect it. Changes in the optical properties of the VO2 thin layer in such structure can be observed in the reflected light in Kretschmann configuration, via a shift in the nadir location due to light absorption at resonance. This optical mechanism occurs at 2mW threshold transition energies and fully saturates at 5mW.

Behavior of surface plasmon polaritons at the interface of metal and a non-integer dimensional (NID) dielectric medium

Abstract The behavior of surface plasmon polaritons (SPPs) at a planar non-integer dimensional dielectric-metal interface has been studied for the first time. The dimension of the interface is shown to have a strong effect on the behavior of SPPs. Dimensions of both the half spaces are different from each other which can be used to distinguish between them besides their different wavenumbers. Lossless dielectric medium has non-integer dimensions while metal has integer dimension. Surface plasmon polaritons (SPPs) only exist for p-polarization and no surface modes exist for s-polarization because the partnering non-integer dimensional dielectric material is homogeneous (Polo and Lakhtakia, 2011). Two methods are used in order to verify the proposed idea. First method is named as so-called indirect method, by using this method, it has been observed that SPP waves are excited only at one incident angle [ θ i = 54.87 ° ] for p-polarized incidence. It has been investigated that the behavior of SPPs changes with change in order of non-integer dimension. The absorption of SPPs increases by decreasing dimensionality for p-polarization at the excitation angle. Second method is named as so-called direct method, according to this method, by solving the presented idea directly using SPP waves fields expressions in NID space, it is conceived that SPPs with same polarization state, but with different phase speeds, attenuation rates, along with propagation lengths can be directed by such interface which incorporates metal and a non-integer dimensional dielectric medium. The results achieved by both methods (so-called indirect and direct methods) complement each other tremendously, validating the efficiency of our proposed concept regarding propagation of SPP waves at a planar non-integer dimensional dielectric-metal interface. Furthermore, the effect of relative permittivity of non-integer dimensional dielectric medium on SPPs is also discussed. The conventional results for integer dimensional space can be recovered as a special case.

Design of efficient surface plasmon polariton modulators using graphene

We design surface plasmon polariton (SPP) absorption modulators using monolayer graphene as the active layer in the 1.5 µm telecommunication wavelength window. Modulation is achieved by electrically modulating the Fermi energy level in the graphene layer. We investigated a silver slab SPP waveguide on graphene and found that there are limitations on the modulation performance as the guided mode only weakly interacts with the graphene layer. To overcome these limitations, we propose a silver–air–silver SPP waveguide on graphene configuration. We show that the latter design can achieve a two times improvement in the figure of merit, defined by the ratio of the extinction ratio to the voltage-off propagation loss, compared to previous indium–tin oxide based SPP absorption modulators.

Coupling between a Molecular Charge-Transfer Exciton and Surface Plasmons in a Nanostructured Metal Grating

The interaction of molecular excitons in organic thin films with surface plasmon polaritons (SPPs) in nanostructured metal electrodes represents a unique opportunity for enhancing the properties of the active layer of a photoconversion device. We present evidence of hybridization between charge-transfer excitons (CTEs) in 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and SPP modes in silver grating nanostructures. Molecular and SPP absorption peaks exhibit avoided crossings in angle-dependent reflectivity experiments, which are verified by electromagnetic-field simulations of the PTCDA-grating structure. Photoluminescence measurements indicate that the radiative decay of the CTE is enhanced. Besides energetic resonance, selective coupling between the SPP and the exciton in this unique case may be aided by the oriented nature of PTCDA into 1-D “molecular stacks” as well as the delocalized nature of the CTE.

Study of coupling efficiency of molecules to surface plasmon polaritons in surface-enhanced Raman scattering (SERS)

Studying the interaction between molecules and surface plasmon polaritons (SPPs) is of great important in understanding surface-enhanced Raman scattering (SERS). While it is known that SERS consists of excitation and emission enhancements, each of them is manifested by several sub-steps which individually also deserve attention. For example, for emission enhancement, the energy from the excited molecules is first coupled to SPPs, which then radiatively scatter to far-field. To understand these two sequential processes completely, differentiating them one by one is necessary. Here, we decouple them and determine the coupling efficiency of molecules to SPPs by using a phenomenological rate equation model. We find the coupling efficiency, defined as the ratio of the coupling rate from molecules to SPPs to the direct Raman decay rate, can be expressed as the SERS intensity ratio and the SPP absorption and radiative decay rates, which all can be determined by polarization- and angle-dependent Raman and reflectivity spectroscopy. As a demonstration, the coupling efficiencies of 6-mercaptopurine to SPPs propagating in Γ-X direction on Ag nanohole array are measured for several Raman emission wavelengths.

A quantitative theory and the generalized Bragg condition for surface plasmon Bragg reflectors

We proposed a quantitative theory based on the surface plasmon polariton (SPP) coupled-mode model for SPP-Bragg reflectors composed of N periodic defects of any geometry and any refractive index profile. A SPP coupled-mode model and its recursive form were developed and shown to be equivalent. The SPP absorption loss, as well as high-order modes in each defect and possible radiation loss, is incorporated without effort. The simple recursive equations derived from the recursive model bridge the reflectance and the transmittance of N periodic defects to those of a single one, resulting in that the computational cost of the geometry optimization or the spectra calculation for N periodic defects is reduced into that for a single one. The model predictions show good agreement with fully vectorial computation data on the reflectance and the transmittance. From the recursive model, the generalized Bragg condition is proposed, which is verified by SPP-Bragg reflectors of various structures. The quantitative theory and the generalized Bragg condition proposed will greatly simplify the design of SPP-Bragg reflectors.

In the diffraction shadow: Norton waves versus surface plasmon polaritons in the optical region

Surface electromagnetic modes supported by metal surfaces have a great potential for use in miniaturized detectors and optical circuits. For many applications, these modes are excited locally. In the optical regime, surface plasmon polaritons (SPPs) have been thought to dominate the fields at the surface, beyond a transition region comprising 3–4 wavelengths from the source. In this work, we demonstrate that at sufficiently long distances SPPs are not the main contribution to the field. Instead, for all metals, a different type of wave prevails, which we term Norton waves (NWs) for their resemblance to those found in the radio-wave regime at the surface of the Earth. Our results show that NWs are stronger at the surface than SPPs at distances larger than 6–9 SPP absorption lengths, the precise value depending on wavelength and metal. Moreover, NWs decay more slowly than SPPs in the direction normal to the surface.