Plasmon Amplitude Research Articles

The fine spectral tuning of plasmon mode and quantum emitter coupling and itscomparison with the dark-hot resonances

Localization of incident fields into very small volumes (hot-spots) allows strong light-matter interactions at the hot spots. This makes path interference effects, Fano resonances, visible. Fano resonances can appear due to the coupling of a bright plasmon (i) to a longer lifetime dark plasmon mode or (ii) to a quantum object (QO) of a much longer lifetime. The second phenomenon provides a very important utility: the voltage tunability of the linear/nonlinear response. The level-spacing of the QO, such as defect-centers and quantum dots, are voltage-tunable which can make a sharp Fano resonance appear and disappear. Here, we compare the two phenomena by solving the equations of motions for the near-field plasmon amplitudes, derived from two different Hamiltonians. While the two plasmon amplitudes look similar to each other, except for the population inversion parameter `$y$', our results show that quantum emitter enables fine spectral tuning of the plasmon amplitude, thus, providing better enhancement.

Plasmonic emission of hybrid Au/Ag bullseye nanostructures

Bullseye nanostructures with different central disk diameters and numbers of concentric rings have been fabricated in Au/Ag metallic films on glass substrates by focused ion beam milling. The Au/Ag bimetallic nanoresonator is expected to provide chemical stability and outstanding plasmonic property. A novel hybrid plasmonic emission has been observed by cathodoluminescence in the scanning electron microscope. It is found that the hybrid plasmon amplitude of the bullseye structure highly depends on the excitation position. The plasmonic intensity is the maximum when the beam is located at the edge of the central disk, and it can be tuned by selecting the disk size and the number of grooves. Additionally, the finite element simulation reveals that the bimetallic bullseye structure strongly confines the optical radiation, and the electric field distribution directly relates to the emission wavelength.

Intensity of Surface Plasmon-Polaritons at a Photonic Crystal–Gold Interface Depending on the Radiation Wavelength

We calculate the amplitudes of surface plasmon-polaritons (SPP) excited at a photonic-crystal–metal interface. Using a three-wave approximation, we evaluate optical fields in the crystal medium. The generation of plasmons at the boundary between the photonic crystal (PhC) and gold substrate is numerically analyzed in the wavelength range of a plane incident wave 400–1,900 nm. The optimum wavelength corresponding to the maximum plasmon amplitude is determined.

Multimode theory of plasmon excitation at a metal – photonic crystal interface

Surface plasmon excitation at a photonic crystal – metal interface is studied taking into account multiple scattering of an initial light wave on a periodical crystal structure. The analysis is focused on calculating characteristics of the eigenwaves in a one-dimensional crystal, which comprise a set of harmonics with the wavevectors separated from each other by the value of the crystal lattice wavevector. Reflection from the crystal – metal interface binds the amplitudes of propagating and evanescent modes. Calculations show that for the dielectric characteristics of a synthetic opal and a substrate made of a real metal with a ruby laser radiation used as the initial wave, the fulfilment of plasmon resonance conditions leads to a local increase in the surface plasmon amplitude by a factor of 6.4 – 9 as compared to the average amplitude of the initial wave. As a rule, the effect can only be obtained for a single surface wave, all other waves being substantially weaker than the main plasmon. There is a specific case where the resonance condition holds for two modes simultaneously. In this case, two oppositely directed fluxes of equal intensity are generated at the interface. The resonance condition breaks at a small deviation of the incident angle of the initial wave θ from the normal direction (|θ| ⩾ 10−4 rad). In the latter case, the picture is asymmetric: at angles |θ| ⩾ 5 × 10−3 rad, only one plasmon remains intensive. The local density of electromagnetic energy at the photonic crystal – metal interface may exceed the corresponding value of the initial wave by a factor of 40 – 80.

Surface plasmon transmission through discontinuous conducting surfaces: Plasmon amplitude modulation by grazing scattered fields

We have studied numerically the diffraction of a surface plasmon polariton (SPP) when it encounters a wide multi-wavelength slit in conducting films. As a jump process a SPP is excited beyond the slit by wave scattering at the second slit edge. The exciting radiation is produced when the incident SPP collapses at the first slit edge. We have found that the transmitted SPP supports inherent and unavoidable interference with grazing scattered radiation; the spatial modulation extends to the fields in the diffraction region where a series of low intensity spots arises. We demonstrate that the SPP generated on the second slab depends on the frequency but not on the wave vector of the collapsed SPP; a SPP is transmitted even when the two metals forming the slit are different. The numerical results were obtained using the Finite Difference Time Domain (FDTD) method with a grid size λ/100.

Metallic Adhesion Layer Induced Plasmon Damping and Molecular Linker as a Nondamping Alternative

Drastic chemical interface plasmon damping is induced by the ultrathin (∼2 nm) titanium (Ti) adhesion layer; alternatively, molecular adhesion is implemented for lithographic fabrication of plasmonic nanostructures without significant distortion of the plasmonic characteristics. As determined from the homogeneous linewidth of the resonance scattering spectrum of individual gold nanorods, an ultrathin Ti layer reduces the plasmon dephasing time significantly, and it reduces the plasmon scattering amplitude drastically. The increased damping rate and decreased plasmon amplitude are due to the dissipative dielectric function of Ti and the chemical interface plasmon damping where the conduction electrons are transferred across the metal-metal interface. In addition, a pronounced red shift due to the Ti adhesion layer, more than predicted using electromagnetic simulation, suggests the prevalence of interfacial reactions. By extending the experiment to conductively coupled ring-rod nanostructures, it is shown that a sharp Fano-like resonance feature is smeared out due to the Ti layer. Alternatively, vapor deposition of (3-mercaptopropyl)trimethoxysilane on gently cleaned and activated lithographic patterns functionalizes the glass surface sufficiently to link the gold nanostructures to the surface by sulfur-gold chemical bonds without observable plasmon damping effects.

(Invited) Particle Size-Dependent Photoelectron Plasmon Loss Features in Deposited Germanium Nanocrystals

The plasmon loss features of deposited and well-characterized germanium nanocrystals with average sizes of 3.5 and 4.5~nm, respectively, are investigated with photoelectron spectroscopy at the Ge~3d core level. We observe a particle size dependence of the surface plasmon amplitude with respect to the bulk plasmon consistent with the changing surface-to-bulk atom ratio. Additionally, the nanocrystal surface plasmons are redshifted with respect to a bulk reference by up to 0.4~eV for 3.5~nm particles. For the bulk plasmons no significant size dependent energy shifts can be observed for nanoparticle sizes down to 3.5~nm.

Effects of plasmon propagation on the profiles of (3/2) omega 0 emissions from laser-produced plasmas

Accounting phenomenologically for the effects arising from plasmon propagation, the profiles of (3/2) omega 0 emissions from a laser-produced carbon plasma have been analyzed. The effects of plasmon propagation on the shift of the peak and on the line broadening of these emissions have been studied in terms of the change in plasmon wave number and reduction in plasmon amplitude in the process of convection from the region of plasmon production to the region of (3/2) omega 0 harmonic generation. It is observed that these effects significantly modify the earlier results based on neglecting the plasmon propagation. Theoretical estimates of the shifts of the peaks and of the linewidths, based on the present analysis, have been compared with experimental results and are observed to be in reasonably good agreement for a suitable choice of parameters characterizing the effects undergone by plasmons in convection.

Cascade Focusing in the Beat-Wave Accelerator

The 2D wave-envelope equations for the beat-wave-cascade system are studied analytically and numerically. An expression for the mean square width of the cascade envelope is obtained, and is used to predict the long-term behavior of the waves. The amplitude of a resonantly driven plasma wave falls significantly over a stage length because of enhanced diffraction of the cascade envelope. Conversely, detuning the pumps from the plasma frequency can lead to focusing of the envelope and a corresponding increase in plasmon amplitude of up to 200% over the same distance.

Modulational instability and its consequences for the beat-wave accelerator.

The modulation instability caused by the coupling of a Langmuir wave to the ion motion is investigated in the domain of large $\frac{{v}_{\mathrm{L}}}{{v}_{\mathrm{te}}}>1$ ratios, where ${v}_{\mathrm{L}}$ and ${v}_{\mathrm{te}}$ denote the pump Langmuir-wave quiver velocity and the electron thermal velocity, respectively. A convenient approximate expression for the growth rate is given for $\frac{{v}_{\mathrm{L}}}{{v}_{\mathrm{te}}}<50{(\frac{A}{Z})}^{\frac{1}{6}}$. The limitation of the beat plasmon growth due to the modulational instability is studied in the context of plasma beat-wave experiments and the maximum beat plasmon amplitude is determined numerically.

Beat Wave Generation of Plasma Waves for Particle Acceleration

The space-time evolution of beat wave generation is studied analytically and numerically. Electromagnetic cascading, collisional damping and relativistic frequency shift of the beat plasmon are taken into account in the model. In particular, detuning and dispersion effects are investigated. The achievable plasmon amplitude depends strongly on the collisional damping. At low electron temperatures, the induced beat wave follows the laser pulse and decays rapidly behind it. At high electron temperatures, amplitude modulation appears and an intense slowly decaying plasmon wake can be excited. The wake formation is controllable by varying the pulse length or by detuning the driver slightly off resonance. The amount of electromagnetic cascading is proportional to the plasmon amplitude and the propagation distance of the pulse. The EM spectra offer excellent diagnostics for beat wave experiments, because plasmon amplitude variations are directly reflected in them.

Plasmons from a gauge invariant effective action for hot gluons

The one-loop effective action for a gluon plasma is calculated in a general covariant background field gauge. The result is expressed in terms of the dielectric constant and the magnetic permeability, which immediately yields dispersion relations for both longitudinal and transverse plasma waves. The plasma frequency is gauge fixing independent and agrees with earlier calculations, while the plasma damping constant is gauge fixing dependent and negative definite. We argue that the result in Landau gauge is of physical significance, and that the calculated exponential growth of the plasmon amplitude is a signal for the breakdown of perturbation theory at scales of order ∼ g 2 T. The relevance of this for the dynamical description of the quark-gluon plasma is discussed.

Possible Reduction of Laser-Fusion Target Illumination by Enhanced Stimulated Raman Plasmon Scattering

When the input irradiance $I$ exceeds a threshold value, two mechanisms cause the stimulated Raman scattering by a plasma to increase as $\mathrm{exp}({g}_{E}{I}^{2}x)$. One mechanism is a nonlinear increase in the plasmon amplitude, and the other is a second-order process of converting two laser photons into a Stokes photon and anti-Stokes photon. In laser fusion, the enhanced scattering by the residual fusion-chamber gas may greatly reduce the laser irradiance at the target. This theoretical possibility should be investigated experimentally.