In this study, we demonstrate the ability to exclude the thermal effect and detect the generation of non-thermal hot carriers by surface plasmon using an AlGaN/GaN high-electron-mobility transistor. We will also provide a theoretical model to explain the detecting mechanism. This proposed platform is very sensitive, which is at least two orders of magnitude more sensitive compared to the previous reports, can detect the hot carriers generated from discrete nanostructures illuminated by a continuous wave light. The quantitative measurements of hot carrier generation also open a new way to optimize the plasmonic nanoantenna design in many applications.
In this work, surface plasmons (SPs) on germanium (Ge) thin film that are excited by cyclotron-motion electron bunch are investigated by finite-difference time-domain simulation. The excited SPs propagate along the electron’s circular orbital. (The electron energy is 30 keV. With the magnitude of external magnetic field being 3 T, the Larmor radius and cyclotron frequency are 200 um and 4.93E11 rad/s, respectively. The optical property of Ge is described by Drude model with the high-frequency dielectric constant, plasma frequency and collision frequency to be set as 16.55, 2.1627E13 and 2.746E11, respectively. And the frequency of SPs is 3 THz.) The dispersion relations of the SPs are obtained by simulation. When adding periodic Ge gratings on the Ge thin film along the electron’s circular orbital, the SPs-manipulated Smith-Purcell radiation (SPR) will emit with the frequency of electron excited SPs. Furthermore, the emitted radiation carries optical angular momentum (OAM) due to the propagation of SPs along the circular orbital. The simulated phase distributions of emitted radiations show spiral patterns, which demonstrates they have different topological charges.
An electron beam passing over metallic gratings can emit Smith-Purcell radiations (SPRs). The electron beam can also excite surface plasmons (SPs) on the metallic surface. Recently, the generation of convergent light beam by SP-manipulated SPRs on metallic chirped gratings has been explored. However, for the one-dimensional gratings, only the emission along the direction of gratings (i.e. the direction of electron beam) is convergent. Therefore, the emission pattern is a line instead of a spot. In this work, the electron beam passing through the arrays of Yagi-Uda nanoantenna for generation of convergent light spot based on SP-manipulated SPR is proposed and investigated by FDTD simulation. The convergent spots that are formed directly above the nanoantenna arrays with different wavelengths are demonstrated. The emission angles controlled by the structure parameters and electron beam energy are also examined. This work provides a way toward practical applications in the fields of optical imaging, holography, cryptography and tunable visible light source.
Breaking optical diffraction limit is one of the most important issues needed to be overcome for the demand of high-density optoelectronic components. Here, a multilayered structure which consists of alternating semiconductor and dielectric layers for breaking optical diffraction limitation at THz frequency region are proposed and analyzed. We numerically demonstrate that such multilayered structure not only can act as a hyperbolic metamaterial but also a birefringence material via the control of the external temperature (or magnetic field). A practical approach is provided to control all the diffraction signals toward a specific direction by using transfer matrix method and effective medium theory. Numerical calculations and computer simulation (based on finite element method, FEM) are carried out, which agree well with each other. The temperature (or magnetic field) parameter can be tuned to create an effective material with nearly flat isofrequency feature to transfer (project) all the k-space signals excited from the object to be resolved to the image plane. Furthermore, this multilayered structure can resolve subwavelength structures at various incident THz light sources simultaneously. In addition, the resolution power for a fixed operating frequency also can be tuned by only changing the magnitude of external magnetic field. Such a device provides a practical route for multi-functional material, photolithography and real-time super-resolution image.
The magnetically controlled planar hyperlens which consists of an InSb-PMMA multilayered structure is proposed and analyzed. The ability of the proposed hyperlens to resolve subwavelength structures at THz region is demonstrated by electromagnetic numerical simulation. The asymmetric field pattern in the hyperlens is caused by the surface magnetoplasmon (SMP) propagating in the InSb-PMMA waveguide. By using transfer matrix method and the effective medium approach of the investigated components, the role of SMP played in the super-resolution is elucidated. Furthermore, the super-resolution of the proposed device under various frequencies is accomplished by merely changing the value of external magnetic field. The proposed device would provide a practical route for multi-functional material, real-time super-resolution imaging, photolithography, and THz imaging.
The scattering of surface plasmon polariton (SPP) waves can be manipulated by various plasmonic structures. The plasmonic structure composed of arranged subwavelength nanobumps on a gold thin film is the promising structure to manipulation SPP wave. By controlling the geometric shape of the structures, the height, position, and pattern of scattered light from SPP wave can be modulated as desired. A clear single focusing spot can be reconstructed at a specific altitude by a particular curved structure with appropriate curvature and adjacent interspacing of nanobumps. The designed light patterns reconstructed by the focusing spot from the arranged curved structures at a specific observation plane are clearly demonstrated.
KEYWORDS: Nanoparticles, Near field optics, Near field scanning optical microscopy, Gold, Near field, Plasmonics, Surface plasmons, Metals, Particles, Polarization
The near-field distribution of plasmonic coupling effect in gold nanoparticle pairs was directly investigated by a nearfield
scanning optical microscope (NSOM) in the fiber-collection mode. NOSM images show that the localized
plasmonic coupling and the electromagnetic field distribution of nanoparticle pairs are systematically influenced by the
interparticle space and axial direction of incident polarization. This observation can facilitate the understanding of
localized hot spots in surface-enhanced Raman spectroscopy in the near field and can be used as a guideline for
fabricating specific nanostructures in controlling the spatial distribution of surface plasmon (SP) modes for ultrasensitive
sensors or photonic devices.
Dipole and quadrupole surface plasmon polariton (LSPP) resonances of gold nanoparticle array were directly
investigated by a near-field scanning optical microscope (NSOM) in the fiber-collection mode. Separated gold
nanoparticles on the quartz substrate were fabricated by nanosphere lithography. Results demonstrate that controlling the
incident polarization and angle of oblique incidence enables to excite dipolar and quadrupolar LSPP at 633- and 488-nm
excitations. This observation facilitates the understanding of LSPP and interactions with nanostructures in the near field
that can be used as a guideline for fabricating nanostructures in controlling spatial distributions of LSPP for ultra
sensitive bio-/chemo-detectors or plasmonic metamaterials.
Surface plasmon-like (SPL) modes are the electromagnetic surface eigenmodes on structured perfect-conductor
surfaces. The standard eigenvalue-solving method is adopted to solve these modes. The fields of the SPL
modes are maximal on the conductor surface and decay exponentially into both the air and the structured
conductor. On thin structured conductors, the SPL mode splits into a high-frequency anti-symmetric mode and
a low-frequency symmetric mode. The SPL modes are slow-wave modes with the frequencies that approach an
equivalent surface-plasmon frequency at large in-plane wavevectors. However, the interhole interaction
prevents the dispersion relation from being generally described by an analytic equation.
The phenomenon of resonant tunneling through thin metal films with periodic narrow grooves is attributed to excitation of the surface plasmon (SP) via the periodic groove structure coupler at the metal surface. In this paper, we will use the particle-in-cell (PIC) plasma simulation method to study this SP-mediated optical tunneling. The PIC method is a time-domain scheme to calculate self-consistently the interaction between the electromagnetic fields and the plasma particles. At the beginning of simulation, the mobile electrons and immobile positive ions are uniformly distributed in the thin Gaussian-shaped-grooved silver film with the plasma density calculated from silver's plasma frequency. The momentum collision-frequency method is employed to model the collision dissipation. For normally incident TM-polarized wave, the transmission coefficients have the maximum values at the LSP resonant modes, similar to the results predicted by Drude model, except for with lower transmission coefficients. Due to the electron dynamics considered in the PIC method, the plasma energy and the trajectories can be monitored during the simulation. The change of the averaged plasma energy with time exhibits some ripple-like patterns, which comes from various competing processes of heating and cooling. But the temperature of the plasma has little effect on the transmission coefficient and the wave tunneling.
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