Plasmon Amplification Research Articles

Amplification of spoof localized surface plasmons on active plasmonic metamaterials

The amplification of spoof localized surface plasmon (LSP) modes has been explored and experimentally demonstrated for the first time by using a kind of active plasmonic metamaterial, which is composed of grooved ring structures with a sub-wavelength amplifier chip as well as the corresponding bias circuit. We have investigated and explained the physical mechanisms of the manipulation of spoof LSP modes in the grooved ring structures with the presence of the bias circuit, where both the integer modes and the half integer order modes can be supported simultaneously. Experimental results at the microwave frequencies show great agreements with the simulation results. It is believed that the active plasmonic metamaterials can find more applications for the purpose of sensing and integrated circuits in microwave and terahertz frequencies.

Surface plasmon field enhancement: excitation by a short pulse or narrow beam of light

With the advance of laser technology, there are many applications exciting surface plasmons with very short pulses of light. We perform a quantitative study of field amplification of surface plasmons excited by short light pulses. The dependence of the maximum intensity of the electromagnetic fields at the metal–dielectric interface is obtained as a function of the pulse duration. A Gaussian light pulse is used as the excitation source and the propagation of this pulse is computed on an attenuated total reflection system for the Kretschmann geometry. The field enhancement produced by the pulse is about 80% of the steady-state case when the width of the pulse is half the decay time of the surface plasmon, and it gets close to 95% when the width is equal to the time decay. We obtain an approximate expression for the field amplification as a function of the pulse width that is close to the exact calculation. Additionally, an approximate expression is obtained for the enhancement of the fields when surface plasmons are excited with a narrow spatial width beam.

Bioderived Three-Dimensional Hierarchical Nanostructures as Efficient Surface-Enhanced Raman Scattering Substrates for Cell Membrane Probing.

In this work, we propose the use of complex, bioderived nanostructures as efficient surface-enhanced Raman scattering (SERS) substrates for chemical analysis of cellular membranes. These structures were directly obtained from a suitable gold metalization of the Pseudonitzchia multistriata diatom silica shell (the so called frustule), whose grating-like geometry provides large light coupling with external radiation, whereas its extruded, subwavelength lateral edge provides an excellent interaction with cells without steric hindrance. We carried out numerical simulations and experimental characterizations of the supported plasmonic resonances and optical near-field amplification. We thoroughly evaluated the SERS substrate enhancement factor as a function of the metalization parameters and finally applied the nanostrucures for discriminating cell membrane Raman signals. In particular, we considered two cases where the membrane composition plays a fundamental role in the assessment of several pathologies, that is, red blood cells and B-leukemia REH cells.

Plasmonic parametric resonance

We introduce the concept of Plasmonic Parametric Resonance (PPR) as a novel way to amplify high angular momentum plasmonic modes of nanoparticles by means of a simple uniform optical pump. In analogy with parametric resonance in dynamical systems, PPR originates from the temporal modulation of one of the parameters governing the evolution of the state of the system. As opposed to conventional localized surface plasmon resonances, we show that in principle any plasmonic mode of arbitrarily high order is accessible by PPR with a spatially uniform optical pump. Moreover, in contradistinction with other mechanisms of plasmonic amplification, the coherent nature of PPR lends itself to a more straightforward experimental detection approach. The threshold conditions for PPR are analytically derived. Schemes of experimental realization and detection are also discussed.

Giant amplification of terahertz plasmons in a double-layer graphene

The amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. The plasmon wave in a symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that, normalized to the wavelength, the terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by four orders of magnitude.

表面等离激元受激辐射方向性调控研究进展

表面等离激元受激辐射方向性调控研究进展

Open Resonator Electric Spaser.

The inception of the plasmonic laser or spaser (surface plasmon amplification by stimulated emission of radiation) concept in 2003 provides a solution for overcoming the diffraction limit of electromagnetic waves in miniaturization of traditional lasers into the nanoscale. From then on, many spaser designs have been proposed. However, all existing designs use closed resonators. In this work, we use cavity quantum electrodynamics analysis to theoretically demonstrate that it is possible to design an electric spaser with an open resonator or a closed resonator with much weak feedback in the extreme quantum limit in an all-carbon platform. A carbon nanotube quantum dot plays the role of a gain element, and Coulomb blockade is observed. Graphene nanoribbons are used as the resonator, and surface plasmon polariton field distribution with quantum electrodynamics features can be observed. From an engineering perspective, our work makes preparations for integrating spasers into nanocircuits and/or photodynamic therapy applications.

Optically Active Ultrafine Au–Ag Alloy Nanoparticles Used for Colorimetric Chiral Recognition and Circular Dichroism Sensing of Enantiomers

Despite a significant surge in the number of investigations into chirality at the nanoscale, especially thiolated chiral molecules capping gold clusters, only limited knowledge is currently available to elaborate the alloying effect on chiroptical behavior of bimetallic nanoparticles (NPs). Also, few successful cases as to the efforts toward the development of chirality-dependent applications on the optically active nanomaterial have been made. Herein, as a positive test case for chiral alloy nanoparticle synthesis, the stable and large chiroptical ultrafine Au-Ag alloy NPs were prepared by reduction of different molar fractions of HAuCl4 and AgNO3 with NaBH4 in the presence of d/l-penicillamine (d/l-Pen). Compared with those of monometallic Au and Ag counterparts with comparable size, the Au-Ag alloy NPs (Ag mole fraction, 70%) obviously displayed the largest optical activities with the maximum g-factors of ∼1.6 × 10-3. Impressively, the Pen-mediated synthesis of chiral Au-Ag alloy NPs possesses a colorimetric self-recognition function and can be used as an incisive circular dichroism (CD) probe toward d- and l-Pen enantiomers. The plasmonic CD signal amplification (ΔICD) shows good linearity with the amount of Pen over the range of 5.0-80.0 μM with a detection limit (3σ) of 1.7 μM for l-Pen and 1.5 μM for d-Pen, respectively. In addition, the sensing system exhibits good selectivity toward d- and l-Pen in the presence of other enantiomers; therefore, it is highly expected that the approach described here would open new opportunities for design of more novel enantioselective analyses of important species related to biological processes.

Enhanced Second Harmonic Generation by Mode Matching in Gain-assisted Double-plasmonic Resonance Nanostructure

We theoretically study the gain-assisted double plasmonic resonances to enhance second harmonic generation (SHG) in a centrosymmetric multilayered silver-dielectric-gold-dielectric (SDGD) nanostructure. Introducing gain media into the dielectric layers can not only compensate the dissipation and lead to giant amplification of surface plasmons (SPs), but also excite local quadrupolar plasmon which can boost SHG by mode matching. Specifically, as the quadrupolar mode dominates SHG in our nanostructure, under the mode matching condition, the intensity of second harmonic near-field can be enhanced by 4.43 × 102 and 1.21 × 105 times when the super-resonance is matched only at the second harmonic (SH) frequency or fundamental frequency, respectively. Moreover, the intensity of SHG near-field is enhanced by as high as 6.55 × 107 times when the nanostructure is tuned to double super-resonances at both fundamental and SH frequencies. The findings in this work have potential applications in the design of nanosensors and nanolasers.

Plasmonic amplification of terahertz radiation in a periodic graphene structure with the carrier injection

Injection pumping of the pristine graphene is a promising alternative to optical pumping, but it is not obvious how to properly combine electronic and plasmonic features in one and the same device in order to obtain the terahertz plasmon amplification in graphene with injection pumping. This paper shows that an amplified plasmon mode can be effectively excited at the plasmon resonance frequencies in an active ungated region graphene with injecting (absorbing) gated parts of the periodic graphene structure. Necessary conditions for the plasmon lasing in the structure are found.

Manipulable and Hybridized, Ultralow‐Threshold Lasing in a Plasmonic Laser Using Elliptical InGaN/GaN Nanorods

Manipulating stimulated‐emission light in nanophotonic devices on scales smaller than their emission wavelengths to meet the requirements for optoelectronic integrations is a challenging but important step. Surface plasmon polaritons (SPPs) are one of the most promising candidates for sub‐wavelength optical confinement. In this study, based on the principle of surface plasmon amplification by the stimulated emission of radiation (SPASER), III‐Nitride‐based plasmonic nanolaser with hybrid metal–oxide–semiconductor (MOS) structures is designed. Using geometrically elliptical nanostructures fabricated by nanoimprint lithography, elliptical nanolasers able to demonstrate single‐mode and multimode lasing with an optical pumping power density as low as 0.3 kW cm−2 at room temperature and a quality Q factor of up to 123 at a wavelength of ≈490 nm are achieved. The ultralow lasing threshold is attributed to the SPP‐coupling‐induced strong electric‐field‐confinement in the elliptical MOS structures. In accordance with the theoretical and experimental results, the size and shape of the nanorod are the keys for manipulating hybridization of the plasmonic and photonic lasing modes in the SPASER. This finding provides innovative insight that will contribute to realizing a new generation of optoelectronic and information devices.

Plasmonic Particles with Unique Optical Interaction and Mechanical Motion Properties

Metal nanoparticles have unique localized surface plasmon resonance (SPR) properties due to the strong interaction of localized surface plasmon polariton (SPP) with incident light. This review will cover some of our recent theoretical and experimental studies on exploring the unique optical interaction and mechanical motion properties of plasmonic particles that originate from SPR enhanced light‐matter interaction. Firstly, the efficient enhancement of both the fluorescence excitation and emission process of dye molecules by the double SPR modes (longitudinal and transverse modes) in gold nanorods, and surface plasmon amplification in metal nanoparticles with gain is discussed. Secondly, it is theoretically demonstrated that two basic physical processes of molecules interacting with light, i.e., the elastic Rayleigh scattering and inelastic Raman scattering, will strongly intertwine and correlate with each other in many plasmonic surface‐enhanced Raman scattering (SERS) and tip‐enhanced Raman scattering (TERS) nanosystems. Thirdly, it is experimentally shown that SPR can enhance the optical force and torque of nanoparticles embedded within non‐intrusive optical tweezers. The work presented in this review shows that plasmonic particles can possess unique optical interaction and mechanical motion properties when their geometries are deliberately controlled.

Theory and technology of SPASERs

Spaser is an acronym for surface plasmon amplification by stimulated emission of radiation. A spaser is effectively a nanoscale laser with subwavelength dimensions and a low-Q plasmonic resonator, which sustains its oscillations using stimulated emission of surface plasmons. The concept of stimulated emission to sustain plasmonic oscillations in a resonator was first described by David Bergman and Mark Stockman in 2003. Using a unified notation, we provide an up-to-date literature review of the major developments and latest advances in spaser theory and carry out a systematic exposition of some of the key results useful to understand the operation of spasers. Our presentation covers both semiclassical and quantum-mechanical formulations of spaser models as well as various designs and technologies demonstrated/suggested to illustrate key aspects of this technology. Even though many advances have already been made in spaser technology, there are many hurdles that need to be overcome to bring this technology up to the level of modern laser technology. We take especially great care to highlight the main challenges facing various spaser designs and the limitations of widely used methods and materials. This review is written for both specialists in the field and a general engineering–physics–chemistry readership.

Tunable random lasing behavior in plasmonic nanostructures

Random lasing is desired in plasmonics nanostructures through surface plasmon amplification. In this study, tunable random lasing behavior was observed in dye molecules attached with Au nanorods (NRs), Au nanoparticles (NPs) and Au@Ag nanorods (NRs) respectively. Our experimental investigations showed that all nanostructures i.e., Au@AgNRs, AuNRs & AuNPs have intensive tunable spectral effects. The random lasing has been observed at excitation wavelength 532 nm and varying pump powers. The best random lasing properties were noticed in Au@AgNRs structure, which exhibits broad absorption spectrum, sufficiently overlapping with that of dye Rhodamine B (RhB). Au@AgNRs significantly enhance the tunable spectral behavior through localized electromagnetic field and scattering. The random lasing in Au@AgNRs provides an efficient coherent feedback for random lasers.

Surface plasmon amplification by stimulated emission of radiation in hyperbolic metamaterials

We study theoretically and numerically spasing conditions and optical dynamics of a composite hyperbolic metamaterial interacting with gain molecules. By combining Maxwell-Bloch equations with Green's function approach, we calculate lasing frequency and threshold population inversion for various gain density in the gain layer. We demonstrate high level of enhancement for photonic density of states in spacious spectral range provided by hyperbolic metastructures. We find that direct dipole-dipole interactions between molecules in the gain layer has a negligible effect on spasing conditions. We identify a region of parameters in which spasing can occur considering these effects.

Spaser and Optical Amplification Conditions in Gold-Coated Active Nanoparticles

Due to their many potential applications, there is an increasing interest in studying hybrid systems composed of optically active media and plasmonic metamaterials. In this work we focus on a particular system which consists of an optically active silica core covered by a gold shell. We find that the spaser (surface plasmon amplification by stimulated emission of radiation) conditions can be found at the poles of the scattering cross section of the system, a result that remains valid beyond the geometry studied. We explored a wide range of parameters that cover most of the usual experimental conditions in terms of the geometry of the system and the wavelength of excitation. We show that the conditions of spaser generation necessarily require full loss compensation, but the opposite is not necessarily true. Our results, which are independent of the detailed response of the active medium, provide the gain needed and the wavelength of the spasers that can be produced by a particular geometry, discussing also...

Adiabatic Amplification of Plasmons and Demons in 2D Systems.

We theoretically investigate charged collective modes in a two-dimensional conductor with hot electrons where the instantaneous mode frequencies gradually increase or decrease with time. We show that the loss compensation or even amplification of the modes may occur. We apply our theory to two types of collective modes in graphene, the plasmons and the energy waves, which can be probed in optical pump-probe experiments.

Operational Regimes in Picosecond and Femtosecond Pulse-Excited Ultrahigh Vacuum SERS.

We report a systematic study performed in ultrahigh vacuum designed to identify the laser excitation regimes in which plasmonically enhanced ultrashort pulses may be used to nondestructively probe surface-bound molecules. A nondestructive, continuous-wave spectroscopic probe is used to monitor the effects of four different femtosecond- and picosecond-pulsed beams on the SER signals emanating from molecular analytes residing within plasmonically enhanced fields. We identify the roles of plasmonic amplification and alignment with a molecular electronic transition on the observed changes in the SER signals. Our results indicate that overlap of the laser wavelength with the plasmon resonance is the dominant contributor to signal degradation. In addition, signal loss for a given irradiation condition is observed only for molecules residing in hot spots above a threshold enhancement. Identification of suitable laser energy density ranges demonstrates the importance of considering these parameters when implementing SERS in the presence of pulsed irradiation.

Impact of local-field effects on the plasmonic enhancement of vibrational signals by infrared nanoantennas.

We have developed an analytical model that provides a mechanistic description of the plasmonic enhancement of vibrational signals by infrared nanoantennas. Our treatment is based on a coupled-point-dipole model which considers the interaction between a point-like nanoantenna and a single vibrational dipole moment. This idealized model is refined in two consecutive steps. The first step generalizes the model to make the treatment of non-point-like nanoantennas possible. The second step deals with local-field effects originating from the mutual interaction of the molecular vibrations. We have compared the results of our model with finite-difference time-domain simulations, and we find that our model predicts both the lineshapes and the amplitudes of the vibrational signals in a quantitative manner. Our analysis shows that the local-field effects play a surprisingly dominant role in the plasmonic enhancement, and we discuss possibilities of engineering this local field in order to further boost the plasmonic amplification.

Plasmonically amplified bioassay – Total internal reflection fluorescence vs. epifluorescence geometry

This paper investigates plasmonic amplification in two commonly used optical configurations for fluorescence readout of bioassays – epifluorescence (EPF) and total internal reflection fluorescence (TIRF). The plasmonic amplification in the EPF configuration was implemented by using crossed gold diffraction grating and Kretschmann geometry of attenuated total reflection method (ATR) was employed in the TIRF configuration. Identical assay, surface architecture for analyte capture, and optics for the excitation, collection and detection of emitted fluorescence light intensity were used in both TIRF and EPF configurations. Simulations predict that the crossed gold diffraction grating (EPF) can amplify the fluorescence signal by a factor of 102 by the combination of surface plasmon-enhanced excitation and directional surface plasmon-coupled emission in the red part of spectrum. This factor is about order of magnitude higher than that predicted for the Kretschmann geometry (TIRF) which only took advantage of the surface plasmon-enhanced excitation. When applied for the readout of sandwich interleukin 6 (IL-6) immunoassay, the plasmonically amplified EPF geometry designed for Alexa Fluor 647 labels offered 4-times higher fluorescence signal intensity compared to TIRF. Interestingly, both geometries allowed reaching the same detection limit of 0.4pM despite of the difference in the fluorescence signal enhancement. This is attributed to inherently lower background of fluorescence signal for TIRF geometry compared to that for EPF which compensates for the weaker fluorescence signal enhancement. The analysis of the inflammation biomarker IL-6 in serum at medically relevant concentrations and the utilization of plasmonic amplification for the fluorescence measurement of kinetics of surface affinity reactions are demonstrated for both EPF and TIRF readout.