Plasmon Radiation Research Articles

Plasmonic Radiation from Spin-Momentum Locking.

Chiral light emission plays a key role in sensing, tomography, quantum communication, among others. Whereas, achieving highly pure, tunable chirality emission across a broad spectrum currently presents significant challenges. Free-electron radiation emerges as a promising solution to surpass these barriers, especially in hard-to-reach regimes. Here, chiral free-electron radiation is presented by exploiting the spin-momentum locking (SML) property of spoof surface plasmons (SSPs). When the phase velocity of free electrons matches that of the SSPs, the SSPs can be excited. By implementing wavenumber compensation through perturbations, the confined SSPs are transformed into free-space free-electron radiation. Owing to the law of angular momentum conservation, this process converts the transverse spin angular momentum of SSPs into the longitudinal spin angular momentum of free-electron radiation during the process, producing pure, tunable, and chiral free-electron radiation across a broad spectrum. This method achieves an optimal degree of circular polarization approaching -1. The innovative methodology can be adapted to SML-enabled guided states or silicon photonics platforms, offering new avenues for achieving chiral emission.

Laser-Induced Periodic Surface Structures on Layered GaSe Crystals: Structural Coloring and Infrared Antireflection.

We study structural and morphological transformations caused by multipulse femtosecond-laser exposure of Bridgman-grown ϵ-phase GaSe crystals, a van der Waals semiconductor promising for nonlinear optics and optoelectronics. We unveil, for the first time, the laser-driven self-organization regimes in GaSe allowing the formation of regular laser-induced periodic surface structures (LIPSSs) that originate from interference of the incident radiation and interface surface plasmon waves. LIPSSs formation causes transformation of the near-surface layer to amorphous Ga2Se3 at negligible oxidation levels, evidenced from comprehensive structural characterization. LIPSSs imprinted on both output crystal facets provide a 1.2-fold increase of the near-IR transmittance, while the ability to control local periodicity by processing parameters enables multilevel structural color marking of the crystal surface. Our studies highlight direct fs-laser patterning as a multipurpose application-ready technology for precise nanostructuring of promising van der Waals semiconductors, whose layered structure restricts application of common nanofabrication approaches.

Measurement of dielectric function and bandgap of germanium telluride using monochromated electron energy-loss spectroscopy

Using a monochromator in transmission electron microscopy, a low-energy-loss spectrum can provide inter- and intra-band transition information for nanoscale devices with high energy and spatial resolutions. However, some losses, such as Cherenkov radiation, phonon scattering, and surface plasmon resonance superimposed at zero-loss peak, make it asymmetric. These pose limitations to the direct interpretation of optical properties, such as complex dielectric function and bandgap onset in the raw electron energy-loss spectra. This study demonstrates measuring the dielectric function of germanium telluride using an off-axis electron energy-loss spectroscopy method. The interband transition from the measured complex dielectric function agrees with the calculated band structure of germanium telluride. In addition, we compare the zero-loss subtraction models and propose a reliable routine for bandgap measurement from raw valence electron energy-loss spectra. Using the proposed method, the direct bandgap of germanium telluride thin film was measured from the low-energy-loss spectrum in transmission electron microscopy. The result is in good agreement with the bandgap energy measured using an optical method.

Selectively Exciting and Probing Radiative Plasmon Modes on Short Gold Nanorods by Scanning Tunneling Microscope-Induced Light Emission

We study the plasmon modes of gold nanorods (as short as ∼100 nm) on a nonmetallic conductive substrate using scanning tunneling microscope-induced light emission (STM-LE) with a nonplasmonic tungsten tip at room temperature in high vacuum (10–7 mbar). The far-field light is identified as the radiative decay of plasmon modes on the nanorods excited by inelastic electron tunneling. The spatial intensity distributions of the first three longitudinal multipolar modes on nanorods are spatially resolved on the order of 10–20 nm. These intensity distributions are related to the radiative electromagnetic local density of states and agree very well with numerical simulations. We discover that the presence of the tungsten tip with a high-dielectric constant influences the line shapes of the plasmon spectra and enhances the strength of the plasmon peaks.

Correction to: Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source

Correction to: Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source

Surface Plasmon Polaritons in Time-Modulated Metallic Materials for Non-Reciprocal Controllable Leaky-Wave Antennas

In this work, we propose using time-modulation in metallic materials, which can be realized through either optical pumps or electric signals, as a coupling mechanism between radiation and surface plasmon polaritons (SPP) without using any optical component. By applying temporal changes in the permittivity of metallic materials, scattered waves yield different frequencies from incident waves, potentially satisfying the continuous wave vector condition and enabling SPP from radiation. The coupling is observed in finite-difference time-domain simulations, where the dispersive metallic materials are modeled using auxiliary differential equations. Under the same modulation, coupling from radiation to SPP and from SPP to radiation differ strongly, showing clear evidence of the non-reciprocity. In addition, the coupling is also actively controllable via strength and frequency modulation. We also demonstrate the coupling at multiple angles, which is difficult to achieve with common methods such as Kretschmann or Otto configurations. The direct and non-reciprocal coupling between radiation and SPP can be beneficial for the application of telecommunication to form transmitting-only and receiving-only leaky-wave antennas in full-duplex transceivers.

Self-organizing half-wave gratings on the surface of silica glass

The interaction of femtosecond laser pulses with the surface of silica glass has been studied. As a result of interference between the incident radiation and surface plasmon polaritons, the formation of self-organizing subwavelength periodic structures with a period of 250 nm was observed. The minimum pulse energy at which recording occurs without surface ablation has been revealed. Keywords: direct laser recording, femtosecond laser pulses, silica, nanogratings.

Revisiting the plasmon radiation damping of gold nanorods.

Noble metal nanoparticles have been utilized for a vast amount of optical applications. For applications that use metal nanoparticles as nanosensors and for optical labeling, higher radiative efficiency is preferred. To get a deeper knowledge about the radiation damping of noble metal nanoparticles, we used gold nanorods with different geometry factors (aspect ratios) as the model system to study. We investigated theoretically how the radiation damping of a nanorod depends on the material, and shape of the particle. Surprisingly, a simple analytical equation describes radiation damping very accurately and allows the disentanglement of the maximal radiation damping parameter for gold nanorods with resonance energy Eres around 1.81 eV (685 nm). We found very good agreement with theoretical predictions and experimental data obtained by single-particle spectroscopy. Our results and approaches may pave the way for designing and optimizing gold nanostructures with higher optical signal and better sensing performance.

Surface plasmonic Cherenkov radiation and symmetry breaking within a coherent nonlinear nanostructure

Nonlinear conversions within the plasmonic structures are important for ultrafast nanophotonics; however, the impact of higher-order dispersion on nonlinear polaritonic efficiency remains unexplored. In this work, we uncover the role of higher-order dispersion and self-steepening on nonlinear surface-plasmon polaritons (NSPPs) within a coherent plasmonic interface that comprises an atomic medium doped on top of a low-loss negative-index metamaterial (NIMM) layer. This dispersion in the atomic medium--NIMM interface yields nonlinear plasmonic phase match and resonant launching of Cherenkov SPPs. We establish time-reversal and $\mathcal{PT}$ symmetry breaking for propagated NSPPs that yield asymmetric plasmonic comb excitation and anomalous plasmonic phase singularities. Our work thereby suggests a fingerprint for nonlinear plasmonic field evolution through the appearance of a Cherenkov field and develops a framework for designing a frequency selector and nanoscopic pulse shaper, which opens prospects for nonlinear nanophotonic applications.

Theoretical analysis and spatial–temporal dynamic simulation of radiation from graphene

In this paper, the terahertz (THz) radiation based on the graphene is studied by theoretical analysis and particle-in-cell (PIC) simulation. We present the transition radiation (TR) of the charged particle traversing a monoatomic graphene layer under arbitrary incidence. By theoretical analysis, we find strongly tunable effects of the radiation field distribution related to the electron’s incident angle, substrate permittivity and graphene conductivity. In the case of the normal incidence, the transition radiation exhibits strong symmetry and considerably more intensive than that at oblique incidence. Furthermore, the plasmon and radiation are simulated by a PIC code with the method of equivalent permittivity to deal graphene. With the PIC code, we observe the spatial–temporal dynamics of plasmon and transition radiation from graphene. Meanwhile, the PIC simulation results of radiation are in good agreement with those by theoretical analysis.

Photonic and plasmonic transition radiation from graphene

We theoretically study the transition radiation in the framework of full Maxwell equations, when a swift electron crosses a monolayer graphene. Based on the Sommerfeld integration, we demonstrate in the frequency domain the spatial distribution of this free-electron radiation, which clearly shows the broadband excitation of both photons and graphene plasmons. Moreover, the radiation spectra for photons and graphene plasmons are analytically derived. We find that the excitation of photons and graphene plasmons favors different particle velocities. To be specific, a higher particle velocity gives rise to the excitation of photons with better directivity and higher intensity, while a lower particle velocity enables the efficient excitation of graphene plasmons in a broader frequency range. Our work indicates that the interaction between swift charged particles and various 2D materials or van der Waals heterostructures is promising for the design of terahertz on-chip radiation sources.

Coaxing unreactive sites

Plasmonic Chemistry Optical excitation of localized surface plasmon resonances can confine light and create electromagnetic (EM) “hotspots” that can increase catalytic reaction rates. Sytwu et al. show how optical excited plasmons can also control the location of the active site. A crossed-bar gold-palladium hydride (Au-PdH x ) plasmonic antenna-reactor system localized EM radiation away from the more reactive PdH x tips. Using in situ environmental transmission electron microscopy, the authors show that changing the illumination wavelength and intensity, along with the surrounding hydrogen gas pressure, could shift dehydrogenation away from the sharp PdH x nanorod tips to the flat middle faces. Science , this issue p. [280][1] [1]: /lookup/doi/10.1126/science.abd2847

ВПЛИВ МАТЕРІАЛУ ПРИЗМИ НА ЧУТЛИВІСТЬ ППР-СЕНСОРІВ

Theoretical analysis of the influence of the sensor prism material on the basis of the phenomenon of surface plasmon resonance (SPR) on its sensitivity and temperature stability of the measurement result is carried out. The analysis was performed for the infrared wavelength range of excitation surface plasmon radiation (980... 1550 nm) using materials for prisms with different refractive indices, namely: glass ceramics Zerodur (n D = 1,5423), optical glasses N-FK51A (n D = 1, 4865) and N-BK7 (n D = 1,5167) with low refractive index, single crystal material CaF 2 (n D = 1.4339), as well as flints N-SF2 (n D = 1,6475) and N-SF11 (n D = 1,7845). The temperature stability of the measurement result was determined for the temperature range from 20 °C to 70 °C, which corresponds to the operating temperature range of most refractometers and commercial SPR sensors. The coefficient of temperature shift of the minimum reflection characteristic for the investigated materials was calculated as the ratio of the magnitude of the angular shift ∆θ to the corresponding change of temperature ∆Т, which caused this shift. The results of the study showed that for all materials, regardless of the refractive index value, the temperature effect decreases with increasing wavelength of radiation. For the material with a lower refractive index (CaF 2 ), the temperature coefficient was 2 times higher than for flint glass (N-SF11). According to the results of the analysis, it was found that the sensitivity of the SPR sensor increases threefold from 52.83 deg./RIU to 173.16 deg./RIU when the refractive index of the prism changes from n D = 1.79 to n D = 1.43. It was also found that increasing the wavelength of the radiation increased both the sensitivity of the SPR sensor and temperature stability regardless of the prism material. The results of the study can be used both to develop new SPR sensors and to optimize the modes of operation of existing ones, in particular the choice of optimal sensitivity at a given range of measurement of the refractive index of the test substance.

Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source

In this work, a graphene-dielectric multilayer hyperbolic metamaterial (GHMM) has been analyzed for the generation of THz Cherenkov radiation (CR) from graphene surface plasmonics (GSP), induced by a moving electron bunch. The structure under analysis consists of a graphene-dielectric multilayer HMM in which the top graphene layer is considered as an interface between air and the underlying multilayer as the substrate. The dispersion analysis of the structure shows the existence of bulk-HMM (BH) and non-bulk HMM (NBH)-region in the $$\omega$$ – $$k$$ space. The structure is found to generate intense CR from the GSP, when the operating point of the electron bunch lies in the BH-region, as the bulk states of the HMM substrate allows the efficient transformation of high-k GSP into THz-CR. The proposed structure can be exploited as a potential candidate for the development of low-voltage, electron beam-driven, ultra-tunable, compact graphene plasmonic Cherenkov THz radiation source. Moreover, the application of the principle of utilizing bulk states of HMM for CR generation has also been discussed for black phosphorous (BP), an emerging 2Dmaterial for the THz to infrared (IR) region.

Theoretical Analysis of a Super-Mode Waveguide and Design of a Complementary Triangular Hybrid Plasmonic Nano-Antenna

The characteristics of a super-mode waveguide-fed nano-antenna composed of a complementary triangular hybrid plasmonic radiation part have been investigated by two methods of finite element and finite-difference time-domain. Also, a symmetric hybrid plasmonic waveguide (SHPW) has been studied theoretically and numerically to analyze short- and long-range fundamental TM super-modes (TMSR and TMLR) that excite the nano-antenna. The obtained propagation length and figure of merit at 193.5 THz are 150.6 μm (1.27 μm) and 691.77 (16.94) for TMLR (TMSR) super-mode, respectively, which confirm the inevitable loss-confinement trade-off of SHPW. These super-modes cause the nano-antenna to have horizontal and bidirectional radiation patterns due to the existence of the in-phase and out-of phase super-modes. The obtained directivities and efficiencies are 9.34 dBi (7.01 dBi) and 96.82% (9.66%) for TMLR (TMSR) super-mode, respectively, at 193.5 THz. Moreover, the horizontal and bidirectional radiation patterns are appropriate for on-chip wireless links with the quality factor of 69.18 and target tracking systems, respectively. The performance of a single row array of nano-antenna on improving the directivity and efficiency has been studied. The proposed SHPW-fed nano-antenna is quite tolerant to practical fabrication errors and compatible with lift-off and electron beam lithography fabrication processes.

Radiative and Non-radiative Surface Plasmon Resonance: Comparison of Real-Time Sensing Performance

The work presents a surface plasmon resonance sensor able to operate the non-radiative and radiative surface plasmons simultaneously. The optical coupling between photons and surface plasmons was mediated by a rough surface, allowing the photon emission by radiative plasmons excitation process. Experimental tests with reversible and irreversible binding were performed, and the results were compared. The SPR curve profile indicates normalized values 1 for SP emission. This feature suggests the involvement of localized SP-states that co-exist in the film with delocalized propagating SP state. The data extraction process and the performance of these two excitation forms are also reported. The higher performance of the non-radiative surface plasmons absorption is by a factor of 4.

Plasmonic Emission of Bullseye Nanoemitters on Bi2Te3 Nanoflakes.

Topological insulators, such as Bi2Te3, have been confirmed to exhibit plasmon radiation over the entire visible spectral range. Herein, we fabricate bullseye nanoemitters, consisting of a central disk and concentric gratings, on the Bi2Te3 nanoflake. Due to the existence of edge plasmon modes, Bi2Te3 bullseye nanostructures are possible to converge light towards the central disk. Taking advantage of the excellent spatial resolution of cathodoluminescence (CL) characterization, it has been observed that plasmonic behaviors depend on the excitation location. A stronger plasmonic intensity and a wider CL spectral linewidth can be obtained at the edge of the central disk. In order to further improve the focusing ability, a cylindrical Pt nanostructure has been deposited on the central disk. Additionally, the finite element simulation indicates that the electric-field enhancement originates from the coupling process between the plasmonic emission from the Bi2Te3 bullseye and the Pt nanostructure. Finally, we find that enhancement efficiency depends on the thickness of the Pt nanostructure.

Spontaneous emission by an ensemble of dipoles coupled to a plasmonic nanoresonator

ABSTRACTSpontaneous emission from ensembles of quantum emitters (QEs) such as atoms, molecules or semiconductor quantum dots can be greatly enhanced by cooperative effects arising from electromagnetic correlations. We describe a cooperative mechanism for emission of light by an ensemble of QEs based upon cooperative energy transfer from QEs to localized surface plasmons in metal-dielectric structures followed by plasmon radiation at a rate that scales with the ensemble size. For large QE ensembles saturating the plasmon mode volume, we derive universal, i.e. independent of local field distribution, expression for cooperative Purcell factor that can by far exceed the field enhancement limits for individual QE in a hot spot. We also derive radiated power spectrum that retains the plasmon resonance lineshape and, in contrast to common cooperative mechanisms, is insensitive to natural variations of QEs' emission frequencies.

Excitation of Propagating Plasmons in a Periodic Graphene Structure by Incident Terahertz Waves

Plasmonic transport is considered as a replacement for electronic transport in low-dimensional systems like field-effect transistors, as plasmons are faster than electrons. Plasmons in graphene are promising for use at THz frequencies, but this research is held back by the primitive state of circuitry for plasmonic devices. This study employs an asymmetric periodic grating to solve the problem of effective excitation of propagating plasmons in graphene. The important role of ``dark'' (weakly radiative) plasmon modes in efficient excitation is revealed. The approach outlined here could help to fill the need for THz plasmon sources, for tomorrow's devices.

Regenerated amplification of terahertz spoof surface plasmon radiation

Regenerated amplification induced by a Fabry–Perot (F–P) cavity is introduced to enhance the interaction efficiency of the free-electron-driven spoof surface plasmon. A direct-current electron beam flies above the meta-grating surface and seeds noise-level plasmonic waves. This weak signal experiences multiple back-and-forth regenerated amplifications in the F–P cavity loaded grating system, and the system outputs a pulsed radiation when the signal leaves the cavity. When compared with the condition without the F–P cavity, the equivalent beam-wave interaction length is effectively extended, and the interaction efficiency is improved by orders of magnitude. The proof-of-principle scheme is verified in both backward-wave and forward-wave modes using the particle-in-cell simulation. This scheme is promising for developing high-efficient on-chip terahertz free-electron radiation sources.