Surface Plasmon Resonance Conditions Research Articles

Magnetic field enhanced terahertz generation from shape-dependent metallic nanoparticles

Abstract This communication deals with the analytical study of terahertz (THz) generation via frequency-difference mechanism using two circularly symmetric Gaussian laser beams with slightly different frequencies ω1 and ω2 and wave vectors k1 and k2 simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles. The mixture, consisting of spherical and cylindrical nanoparticles, is placed in a host medium under the influence of an externally applied static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on electrons of the nanoparticles, causing them to experience nonlinear oscillatory velocity. Further, the consequent nonlinear current density excites terahertz radiation at the beat frequency (=ω1 - ω2). Magnetic field influences the surface plasmon resonance condition associated with electrons of the nanoparticles due to enhancement in ponderomotive nonlinearities, thereby causing an increment in the amplitude of generated THz field. It is observed that the generated THz radiation has a strong dependence on the shape and size of the nanoparticles in addition to the magnetic field strength. Cylindrical nanoparticles provide greater THz amplitude than spherical nanoparticles due to additional resonance modes, and combining both kinds of nanostructures further enhance the amplitude. THz radiations play an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.

Surface phonon resonance: A new mechanism for enhancing photonic spin Hall effect and refractive index sensor

Abstract Metal-based surface plasmon resonance (SPR) plays an important role in enhancing the photonic spin Hall effect (SHE) and developing sensitive optical sensors. However, the very large negative permittivities of metals limit their applications beyond the near-infrared regime. In this work, we theoretically present a new mechanism to enhance the photonic SHE by taking advantage of SiC-supported surface phonon resonance (SPhR) in the mid-infrared regime. The transverse displacement of photonic SHE is very sensitive to the wavelength of incident light and the thickness of SiC layer. Under the optimal parameter setup, the calculated largest transverse displacement of SiC-based SPhR structure reaches up to 163.8 μm, which is much larger than the condition of SPR. Moreover, a NO2 gas sensor based on the SPhR-enhanced photonic SHE is theoretically proposed with the superior sensing performance. Both the intensity and angle sensitivity of this sensor can be effectively manipulated by varying the damping rate of SiC. The results may provide a promising paradigm to enhance the photonic SHE in the mid-infrared region and open up new opportunity of highly sensitive refractive index sensors.

МОДЕЛЮВАННЯ ПЛАЗМОННИХ ВЛАСТИВОСТЕЙ ЧАСТИНОК МОНОСУЛЬФІДУ МІДІ В БЛИЖНЬОМУ ІЧ ДІАПАЗОНІ

This paper is devoted to the theoretical study of the extinction spectra of copper monosulfide particles under conditions of localized surface plasmon resonance. The study was conducted for plasmonic copper monosulfide particles of spherical and ellipsoidal shapes of variable size in media with different values of the refractive index. The simulation results reveal that increasing the radius of CuS nanoparticles leads to a significant enhancement in the amplitude of the plasmon peak and a shift of the peak towards longer wavelengths. It was investigated how the positions of the extinction peaks on the spectral scale and their amplitudes change when the particles deviate from the spherical shape. Simulations were performed for spherical and elongated ellipsoidal particles with fixed cross-sectional radius and variable length. Specifically, we varied the length of the major axis while keeping the lengths of the minor axes constant. It is shown that the deviation from the sphericity of the particles will affect both the position of the extinction maximum on the spectral scale and the shape of the spectral curve. An increase in the ratio of the ellipsoid semi-axes lengths leads to a significant increase in the amplitude of the extinction peak and its shift to the long-wavelength region. Besides, the position of the plasmonic peak on the spectral scale is influenced not only by the geometric parameters of the particles such as size and shape but also by the dielectric properties of the surrounding medium, including its refractive index. We assess the impact of changing the refractive index of the surrounding medium on the shape, amplitude, and position of the extinction maxima of CuS nanoparticles. It is showed that increasing the refractive index of the surrounding medium leads to a significant shift of the plasmon resonance peak into the long-wavelength region of the spectrum an increase in the peak width, and a decrease in its amplitude. Thus, ellipsoid copper monosulfide particles show improved surface plasmon characteristics compared to spherical ones and can be effectively used in the near-infrared spectral region.

Al-doped ZnO based long range optical fibre sensor for efficient low refractive index detection

In this article, a simulation of surface plasmon resonance (SPR) based Al-doped ZnO (AZO) coated long-range low refractive index detections in infrared range sensor by the finite element method is presented. Plasmonic material Al-doped ZnO is used for SPR conditions in the desired range. The effects of AZO layer thickness on resonance wavelength, confinement loss, and sensitivity of the proposed sensor are examined for different analyte refractive indices. We have optimized coated AZO layer thickness of 90 nm and width of 124.70 µm in our work. The proposed infrared sensor has achieved refractive index sensitivity 2000–16,000 nm/RIU, and the resolution $$5.00\times {10}^{-5}-6.25\times {10}^{-6}\, \mathrm{RIU}$$ for the analyte’s refractive index range from 1.23 to 1.37. The proposed sensor may be utilized for detecting low refractive index organic chemicals, biomedical, and liquid foods and may also be used in other sensing applications.

Plasmon driven super-high HER activity of electronic structure and lattice strain engineered single atomic layer Pd@Au nanorods

The development of efficient catalysts with low energy consumption has always been a key issue for sustainable hydrogen energy. Here, we report a catalyst comprising a single atomic Pd layer deposited on Au nanorods (ML-Pd@Au NRs) that shows a super-high HER activity and ultra-low overpotential under localized surface plasmon resonance condition. The Au NR plays triple determining roles in HER performance via adjusting the electronic structure and lattice strain of Pd that effectively reduces the adsorption energy of H-adatoms, eliminating the penetration of H adatoms in multilayer Pd crystal that decreases the H adatoms diffusion kinetics, and providing high energetic hot charge carriers under near-IR light irradiation that decreases the activation energy and onset potential of HER. The single atomic Pd layer on Au NRs ensures the hot electron transfer as the main dissipation pathway of the plasmonic hot charge carriers for HER. Thus, under near-IR light irradiation, HER on ML-Pd@Au NRs occurs with a high mass activity of 17.47 mA mg−1 at 100 mV and a very low overpotential of 13 mV at 10 mA cm−2, which are superior to the commercial Pd/C and commercial Pt/C catalysts under the same conditions.

Optical Characterization of Thin Films by Surface Plasmon Resonance Spectroscopy Using an Acousto-Optic Tunable Filter

The paper presents the application of the acousto-optic tunable filter (AOTF) in surface plasmon resonance (SPR) spectroscopy to measure the optical thickness of thin dielectric coatings. The technique presented uses combined angular and spectral interrogation modes to obtain the reflection coefficient under the condition of SPR. Surface electromagnetic waves were excited in the Kretschmann geometry, with the AOTF serving as a monochromator and polarizer of light from a white broadband radiation source. The experiments highlighted the high sensitivity of the method and the lower amount of noise in the resonance curves compared with the laser light source. This optical technique can be implemented for nondestructive testing in the production of thin films in not only the visible, but also the infrared and terahertz ranges.

Interaction of spatial-Gaussian lasers with the magnetized CNTs in the presence of DC electric field and enhanced THz emission

The interaction of spatial-Gaussian lasers with magnetized carbon nanotubes (CNTs) in the presence of a DC electric field is shown to broaden the surface plasmon resonance effectively. The prime feature of the interaction of lasers with magnetized CNTs is that when the electron cylinder of CNT is shifted with respect to the ion cylinder, the space charge electric field is developed in the overlapped region and results in the restoration force of the electrons. The restoration force along with the ponderomotive and magnetic forces assist to increase the nonlinear current which is further enhanced by the drift velocity acquired by the electrons of CNTs due to the applied static electric field. This action is also responsible for the enhanced THz yield at surface plasmon resonance condition where is the polarization coefficient, is the relative permittivity of the dielectric substrate, is the cyclotron frequency of CNT electrons and is the plasma frequency. The study reveals that THz generation from the magnetized CNTs may be a promising source for the detection of dangerous chemicals like royal demolition explosive (RDX), pentaerythritol tetra-nitrate (PETN), trinitrotoluene (TNT), etc.

Luminous, relativistic, directional electron bunches from an intense laser driven grating plasma

Bright, energetic, and directional electron bunches are generated through efficient energy transfer of relativistic intense (~ 1019 W/cm2), 30 femtosecond, 800 nm high contrast laser pulses to grating targets (500 lines/mm and 1000 lines/mm), under surface plasmon resonance (SPR) conditions. Bi-directional relativistic electron bunches (at 40° and 150°) are observed exiting from the 500 lines/mm grating target at the SPR conditions. The surface plasmon excited grating target enhances the electron flux and temperature by factor of 6.0 and 3.6, respectively, compared to that of the plane substrate. Particle-in-Cell simulations indicate that fast electrons are emitted in different directions at different stages of the laser interaction, which are related to the resultant surface magnetic field evolution. This study suggests that the SPR mechanism can be used to generate multiple, bright, ultrafast relativistic electron bunches for a variety of applications.

Optical-chemical sensors based on plasmonic phenomena modulated via micro-holes in plastic optical fibers filled by molecularly imprinted polymers

A novel optical chemical sensing approach is presented and successfully tested in this work. The device is based on modified plastic optical fibers (POFs), with molecularly imprinted polymers (MIPs) inside, coupled with a surface plasmon resonance (SPR) in POFs. The MIP is deposited in a microstructured POF platform which is used to launch the light into the SPR-POF sensor. Therefore, the SPR sensor is not directly in contact neither with the MIP layer, nor to the sample under examination and the sensor system has been made insensitive both to the MIP thickness and refractive index. The chemical sensing platform interacts with the analyte changing the effective refractive index of the POF core, and the SPR conditions at the SPR sensor. As a proof of concept, a MIP receptor specific for furfural (2-FAL) in water is used to realize the proposed sensing principle. A detection limit (LOD) of fractions of μg/l was obtained, about 2 orders of magnitude lower than that obtained with another SPR-POF sensor where the same MIP receptor was directly deposited upon the SPR-sensitive surface to detect 2-FAL in water.

Synthesis of copper nanoparticles on cellulosic fabrics and evaluation of their multifunctional performances

Two different kinds of copper nanoparticles (CuNPs) (brown colour and greenish colour) were synthesised by using simple solution route and applied by exhaust method to achieve multidimensional functionalization on one of the most popular cellulose materials e.g., cotton fabric. The synthesised CuNPs imparted different colours to the said textile due to different conditions of synthesis and localized surface plasmon resonance. Physico-chemical characterizations of the synthesized nanoparticles were performed by using scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis whereas the optical properties of the nanoparticles were studied using UV–visible spectroscopy. The prepared CuNPs of both the types demonstrated very good antimicrobial activity up to 97%. In addition, cotton fabric treated with CuNPs showed very high catalytic activity for reduction of 4-nitroaniline (4-NA) in presence of sodium borohydride to phenylene diamine (4-PD). Washing durability and rubbing fastness of the treated fabric have also been measured by following standard testing methods and found to be very good with a rating 4.Graphical abstract

Signal Amplification of the Transient Response Measured by the Subnanosecond Pump-Probe Method Based on Surface Plasmon Resonance.

A pump-probe system with a subnanosecond pulsed laser is expected to be a compact and inexpensive transient spectroscopic system that enables nondestructive and noncontact evaluations of the physical properties. However, an improvement in the sensitivity and a theoretical model to complement the measurement signal are necessary to obtain the transient signal precisely because of the low sensitivity and large time resolution. We have developed a highly sensitive pump-probe system with a subnanosecond pulsed laser that combines signal amplification based on surface plasmon resonance (SPR) in this study. An integrated theoretical model of the transient response obtained by a subnanosecond pump-probe under the SPR condition was proposed. Our model consisted of the profile descriptions of the used pulse source, temperature change, generated thermoelastic stress, estimated permittivity change in the metal film, and estimated reflectivity change. The theoretical estimations in the time domain and the incident angle dependence were compared with those of the experimental results to verify our theory. As a result, the estimations were well in agreement with the experimental results. Moreover, the signal-amplification mechanism based on SPR was discussed using our theory. The amplification was caused by the broadening of the resonant curve of SPR and the shift of the resonant angle, which seemed to come from the increase in the electron-phonon scattering rate and the thermal expansion of the metal film, respectively. A clear mechanism of SPR-based signal amplification of the subnanosecond pump-probe was identified through experimental and theoretical approaches.

Selective ultrasensitive FBG-SBL chemosensor for detection of copper ions in water resources based on plasmon resonance energy transfer

In this study, the gold (Au) coated fiber Bragg grating (FBG) probe decorated with Schiff base ligands (SBL) with variable denticity is proposed as a susceptible sensor for monitoring the copper ions (Cu2+) concentration in an aqueous solution. The sensing principle can be attributed to the interaction of the SBL coated on Au/FBG, which serves as anionic chelates with Cu2+, altering the environment refractive index and changing the surface plasmon resonance (SPR) condition. The sensitivity and limit of detection (LOD) through a Bragg wavelength shift are measured to be 23.1 pm/µM and 0.07 µM respectively, with a dynamic range of up to 4 µM (µM, 2.5 ppm), which is within the acceptable limit specified by the World Health Organization (WHO) for safe drinking water (1.3 ppm). The probe shows an assertive coordination behaviour towards Cu2+ for selective detection compared to other heavy metals. Excellent reusability (6 trial times) and specificity and portability make FBG-SBL chemosensor suitable for online monitoring of water resources.

Achieving geometrical enhancement of fields in chiral nanoplasmonics using fractional calculus

In this paper, an analytical approach has been developed for electromagnetic field enhancement in fractal nanostructure under the quasi-static limit. A metallic fractal embedded in an unbounded, isotropic, and lossless chiral medium has been treated under this approach. In addition, the field enhancement is also noted by imposing surface plasmon resonance condition. To achieve the desired objective, Maxwell divergence equations are considered and written in an appropriate form by mean of fractional calculus.

Spectroscopic ellipsometry methods for brevetoxin detection

The spectroscopic ellipsometry (SE), and attenuated internal reflection spectroscopic ellipsometry (TIRE) are promising methods in label-free biosensing applications. An ellipsometer running under surface plasmon resonance (SPR) conditions has unique advantages over other SPR-based methods in terms of sensitivity and real-time/label-free measurement capability. In this study, both SE and TIRE-based brevetoxin B (BTX) sensors were developed using two anti-BTX aptamers reported before. A new aptamer sequence was also derived from these two antiBTX aptamers using predictive modeling tools and an exclusion method. All three antiBTX aptamers' analytical performances were quite competitive in terms of both detecting range and detection limits. However, the selectivity of the previously reported aptamers against analogs of BTX was poor at low detection ranges, especially for okadaic acid. Furthermore, the selectivity of the derived aptamer was lower than its predecessors. The sensors were capable of detecting BTX in the range of 0.05 nM–1600 nM in the TIRE and 0.5 nM–2000 nM in the SE configuration. The detection limits of the sensors were 1.48 nM (1.32 ng/mL) and 0.80 nM (0.72 ng/mL) for SE and TIRE configurations, respectively. Both configurations have been used successfully to detect BTX standards spiked into real fish and shrimp samples.

Analysis of D-Shaped Optical Fiber based Corrosion Sensor Using LMR and SPR Effects

This article presents the proposed structure and the simulation results from analytical and numerical modeling of two corrosion sensor elements in D-shaped optical fiber: one based on the lossy mode resonance (LMR) effect and the other based on the effect of surface plasmon resonance (SPR). In the first sensor element, a bilayer of titanium dioxide – aluminum (TiO2-Al) is deposited on the D-shaped region, operating in LMR conditions, while, in the second sensor element, an aluminum (Al) monolayer is deposited under D-shaped region, operating in SPR condition. The sensor elements can operate separately, enabling simultaneous two-parameter measurements at two different points, or they can operate in cascade configuration, increasing the operating range and sensitivity of the sensor set. The D-shaped region of the optical fiber is modeled with an analytical model based on the Fresnel formulation, and also with a numerical model, which uses the finite element method with the COMSOL Multiphysics 5.2 software. The transmission of light through the D-shaped region causes peculiar variations in each light polarization in each sensor element, depending on the metal thickness. Both regions are subject to a corrosive environment. The sensor elements are evaluated separately and in cascade configuration, using polarized and nonpolarized light. Finally, the obtained results show two resonance valleys for the same operating wavelength, resulting in a higher operating range with high sensitivity, compared to other corrosion sensor structures found in the literature.

Resonance-enhanced second harmonic generation via quantum dots integrated with Ag nanoarrays

The metal nanoarray can couple the excitation light energy to the surface, resulting in local electromagnetic field enhancement due to the resonance effect. This is beneficial to the generation of nonlinear optical processes which depend on electromagnetic resonance enhancement, taking advantage of the field enhancement properties of metal nanoarray. Here, silver nanoperiodic arrays are integrated with AgInS2 quantum dots (QDs) to enhance the second harmonic generation (SHG) process of QDs. The experimental results show that the enhancement factor of SHG is 8.8-fold in the condition of surface plasmon resonance. In contrast, the second harmonic emission from pure quantum dots is very weak. The simulation reveals that the second harmonic enhancement is caused by the resonance between the incident laser and the Ag nanoarray. The experimental results show that it is feasible to generate a highly efficient nonlinear optical process of QDs assisted by metal nanoarray. This is beneficial for extending the nonlinear applications of quantum dots.

New features in the surface plasmon induced photon drag effect in noble metal thin films

We study light–matter interactions leading to the generation of photon drag voltage under surface plasmon resonance conditions in noble metal thin films and observe important effects, which provide opportunity for condensed matter theorists to critically evaluate theoretical models. The drag voltage originates from a force that arises because of the transfer of momentum from incident light to electrons. This transfer of photon momentum leads to an electric current, which in turn results in the generation of drag voltage. The effect is particularly enhanced under surface plasmon resonance conditions and thereby reinforces the interaction between light and collective oscillations of the surface charges. We observe relatively high voltages with a nonlinear dependence on laser intensity. In disagreement with previous results, we do not observe a reversal in the sign of the voltage when the direction of the incident laser momentum is reversed. Qualitative analyses of the data show that the hydrodynamic model of laser-induced drag voltage does not work: the hydrodynamic model predicts voltages that are nine orders of magnitude lower than our measurements. However, there is reasonable consistency between the results of the measurements and numerical simulations.

Kinetic theory of electroconductivity of metal nanoparticles in the condition of surface plasmon resonance

In recent years, there has been increasing interest in the study of the optical properties of metallic nanostructures. This interest is primarily related to the practical application of such nanostructures in quantum optical computers, micro- and nanosensors. These applications are based on the fundamental optical effect of excitation of surface plasmons. Surface plasmons are electromagnetic excitations of electron plasma of metals at the metal-dielectric interface, which are accompanied by fluctuations in the surface charge density. The consequence of this phenomenon is surface plasmon resonance (SPR) – an increase in the energy absorption cross-section of a metal nanoparticle as the light frequency (laser irradiation) approaches to the frequency of the nanoparticle SPR. The SPR frequency for metallic nanoparticles in a dielectric matrix is found. Using the kinetic subdivision, the components of the optical power tensor for ellipsoidal metal nanoparticles were developed.

In Ukrainian

In recent years, interest in studying the optical properties of metallic nanostructures has grown. This interest is primarily related to the possibility of practical application of such nanostructures in quantum optical computers, micro- and nanosensors. These applications are based on the fundamental optical effect of surface plasmon excitation. The consequence of this phenomenon is surface plasmon resonance (SPR) - an increase in the cross section of energy absorption by a metal nanoparticle as the frequency of incident light (laser radiation) approaches the SPR frequency of the nanoparticle. Plasmon structures are used to improve the efficiency of thin-film SC. In such structures, metal nanoparticles can primarily act as additional scattering elements for the long-wavelength component of sunlight illuminating SC. As a collective phenomenon, SPR can be described using kinetic approaches, ie using the Boltzmann kinetic equation for the conduction electrons of metal nanoparticles. In this work, the theory of SPR based on the kinetic equation for the conduction electrons of nanoparticles is constructed. to the well-known results derived from the Drude-Sommerfeld theory. Second, the kinetic method makes it possible to study metal nanoparticles with sizes larger or ptical conductivity tensor for spheroidal metal nanoparticles. It is shown that the effect of nanoparticle asymmetry on the ratio of the components of the optical conductivity tensor differs not only smaller than the average electron free path length. The developed theory is used to calculate the oquantitatively but also qualitatively in high-frequency and low-frequency surface scattering. It was found that in metal nanoparticles in a dielectric matrix, under SPR conditions, the full width of the SPR line in a spherical metal nanoparticle depends on both the radius of the particle and the frequency of the electromagnetic (laser) radiation exciting this SPR. It is shown that oscillations of the SPR line width with a change in the dielectric constant of the medium in which they are located can be observed in metal nanoparticles. The magnitude of these oscillations is greater the smaller the size of the nanoparticle and increases significantly with increase. As the radius of the spherical nanoparticle increases, the width of the SPR line decreases significantly and prevails around a certain constant value in media with a higher value of dielectric constant.

Saxitoxin aptasensor based on attenuated internal reflection ellipsometry for seafood

In this study, we proposed label-free saxitoxin (STX) sensor using STX specific aptamer in combination with spectroscopic ellipsometry (SE) and attenuated internal reflection (AIR) spectroscopic ellipsometry method which is operated under surface plasmon resonance (SPR) conditions. Besides the other surface plasmon resonance-based applications, AIR-SE applications have unique advantages in terms of sensitivity and it was used herein for real-time detection of STX in real samples. Another method, SE, was also used and compared with AIR-SE. Analytical performances were satisfactory with low detection limits and a wide detection range. Limit of detection was 0.01 ng/mL for AIR-SE and 0.11 ng/mL for SE. Both proposed sensors were operable in 0.01 nM–1000 nM STX range. These methods were also used for the accurate, selective, and sensitive detection of STX from fish and shrimp samples.