Resonance Peak Position Research Articles

Active near-infrared wavefront engineering employing geometric phase metasurfaces combined with phase-change materials

In recent years, with the remarkable development of micro–nano technology, phase change materials (PCMs) with superior tunable and nonvolatile functionality are integrated into metasurfaces, which has aroused huge interests among scientific communities. However, the imaginary part of refractive index of PCMs in the crystalline phase is large in the near-infrared region (NIR), leading to the strong absorption of device and limiting the development of the PCMs in the NIR. Here, we propose and investigate the hybrid metasurface with asymmetric double-split rings. We use PCM and silica (SiO2) as the composite dielectric layer, which can efficiently reduce the impact of the high imaginary part of the refractive index PCM in the crystalline phase. Moreover, metasurfaces with two types can obtain two different resonances. Furthermore, by inducing the phase change of the PCM, we can move the short-wavelength resonance peak to the position of another long-wavelength resonance peak. Meanwhile, we can add two sets of different phases to two different types of metasurfaces. Thus, the active metasurface based on the PCM can be used to achieve the active wavefront in the NIR. Hence, the proposed metasurface based on the PCM can be applied in tunable beam switching, reconfigurable holography, and other reconfigurable optical components in the NIR.

The influence of confined acoustic phonon on the quantum Peltier effect in doped semiconductor superlattice in the presence of electromagnetic wave

Based on the kinetic equation method, the quantum Peltier effect has been theoretically studied under the influence of confined acoustic phonon in doped semiconductor superlattice in the presence of the electromagnetic wave (laser radiation). There were complicated dependences of the analytical expression of the Peltier coefficient (PC) on quantities such as doped concentration of the superlattice, amplitude of the laser radiation, the cyclotron frequency of electrons and temperature of the system. In detailed consideration, the quantum number m was changed in order to characterize the influence of confined acoustic phonon. When setting the m to zero, we obtained the results that corresponded to the case of unconfined phonon. The theoretical results have been numerically evaluated and discussed for the GaAs:Si/GaAS:Be doped semiconductor superlattice (DSS). We found the oscillation of the PC according to enhancement of cyclotron frequency of electrons. Moreover, position of resonant peaks has shifted under the influence of phonon confinement. In the case of low doped concentration (n D), the PC decreased in non-linear way; then it reached a negative constant in high n D value. The non-linear change of the PC also has been detected when investigating its dependence on the laser amplitude. All numerical results have shown that the magnitude of the PC decreased due to the increase of phonon confinement effect. In short, the confinement of acoustic phonon caused the change of the quantum Peltier effect in DSS of GaAs:Si/GaAS:Be in quantitatively as well as qualitatively.

Multiple adjustable Fano resonance based on double half ring resonator and its application

In this paper, a compact nanostructure is proposed that includes a metal insulator metal (MIM) waveguide with a metal wall and a side-coupled half-ring resonator. The transmission characteristics of the system are studied numerically by using the finite element method (FEM). The simulation results show that double Fano resonances can be produced in the structure, and the two Fano resonances can be controlled independently by two different half rings. The position and intensity of the Fano resonance peaks can be adjusted flexibly and easily by changing the refractive index of the filling medium. The waveguide is sensitive to the refractive index of the filling medium inside the resonator and the maximum sensitivity and figure of merit (FOM) are 1260 nm/RIU and 26,000 respectively. By adding two more half-rings below, four independently adjustable Fano resonances are obtained. The structure of this paper can be used as a sensor which can detect the glucose concentration, so it has a broad application prospect in biomedical and chemical sensing fields.

Interplaying Role of Particle Size and Polymer Layer Thickness on the Large Tunable Optical Response of Polymer-coated Silver Nanostructures

The interplaying role of particle size and polymer layer thickness on the tunable optical response of polymer-coated Ag nanoparticles (NPs) has been studied experimentally and theoretically. A large redshift ( $$\sim$$ 38 nm) of surface plasmon resonance (SPR) peak position has been observed experimentally for Ag NPs of sizes in the range of 8−18 nm synthesized by polyol process with the varying concentration of metal precursor (AgNO $$_{3}$$ ) and using a surfactant (PVP) as a stabilizer. The observed large redshift of the SPR peak position of Ag NPs coated with PVP has been argued due to mainly change of NP size as well as change of local dielectric environment in the vicinity of the Ag NPs. The experimentally observed SPR peak shift has been explained by considering the system as a metal-core polymer-shell nanostructure. The change of local dielectric environment of the surrounding of the NPs is due to the change in the PVP layer on the NPs. Such observation has been confirmed through the theoretical studies considering the changes of NP size as well as the effective thickness of the PVP layers on the NPs. The SPR peak of the system with core-shell nanostructure has been found to vary linearly with the increase in radius of core and thickness of shell together. However, it changes exponentially with particle size alone. It has been found from a detailed study that the change in the ratio of radius of core and thickness of the shell is responsible for the observed redshift. Thus, the redshift of SPR peak position of Ag NPs cannot be justified by only considering the increase in particle size. Rather shell thickness has been found to play a prominent role in the SPR peak shift. This study can be used to understand the optical response of noble metal NPs coated with organic polymers.

On the quantitative optical properties of Au nanoparticles embedded in biological tissue phantoms

We systematically investigated and quantified how gold (Au) metal nanoparticles (NPs) optical spectra change upon introduction into biological tissue phantoms environment, in which the AuNPs can agglomerate. Quantitative knowledge of how the AuNPs spectra and plasmon resonance wavelength change inside a phantom environment can provide many in-vitro and in-vivo plasmonic NPs-mediated applications. Because the plasmonic properties of metal NPs are dependent on their size, morphology, concentration and local environment, tuning the incident photon wavelength may increase the AuNPs plasmonic properties, on which applications such as plasmonic photothermal therapy and photonic gene circuits are based. Quantitatively analyzing optical absorption and scattering data, we were able to observe changes in the resonance peak positions and breadths, which are related to the distribution of the spherical AuNPs within the chitosan phantoms as a function of the particles size and concentration.

Cross section measurement of neutron capture reaction based on back-streaming white neutron source at China spallation neutron source

The data of neutron capture cross section are very important for the research of nuclear astrophysics, advanced nuclear energy development. Owing to the limitation of neutron source and detector, the experimental data of neutron capture cross section in an energy range of 1 eV–10 keV were almost blank in China. The first Chinese gamma-ray total absorption facility has been constructed in the key laboratory of nuclear data at China institute of atomic energy, which consists of 40 BaF<sub>2</sub> detector units. The BaF<sub>2</sub> crystal shell with a thickness of 15 cm and an inner radius of 10 cm covers 95.2% of the solid angle. On-line measurement method of neutron capture reaction cross section is established on the back-streaming white neutron source of China spallation neutron source by using the upgraded facility. The cross section of <sup>197</sup>Au neutron capture reaction is measured for the first time under the experimental condition of irregular 30 mm neutron beam spot. The measured position of resonance peak is well consistent with the relevant data of ENDF evaluation database, which verifies the reliability of the measurement device and measurement technology, and thus laying the foundation for the acquisition of high precision cross section in future.

Anomalous Characteristics of Ion Emission during Fracture of Polymers

Current–voltage characteristics of ion emission during mechanical fracture of polymer films (polyethylene terephthalate, polyimide, polyphenylene ether) in high vacuum have been studied. Positive ions appear at a pulling potential of 100–200 V, after which their number monotonically increases with potential until saturation. Negative ion emission starts at <<200 V and exhibits resonance behavior within the 0–50 V interval, whereby the resonance peak position depends on the nature of polymer. The resonance character of negative ion emission found corresponds to the proposed physical mechanism of ion formation.

Study on mode shifts of localized surface plasmon cavity in Ag nanowire tetramer

The interaction between noble metal nanowires can induce the local surface plasmonic resonance effect, thereby enhancing the distribution of electric field in the nanostructures, which is of very important significance in improving the fluorescence characteristics and enhancing the sensitivity of sensors. In this study, we design several types of tetramers based on precious metals Ag nanostructures, including cylindrical and prismatic Ag tetramers, and by changing the arrangement and the rotation angle of prism nanowires, we simulate the rotation-angle dependent electric field distribution and electric field intensity of &lt;i&gt;X&lt;/i&gt; component , and also discuss the physical mechanism of the relationship between the resonant peak position of absorption spectrum and the change of mode volume. The results show that in the Ag nanowires tetramer structure, the electric field in the cylindrical structure is not enhanced obviously, but the electric field in the prismatic structure is greatly enhanced, and an electric dipole resonance mode is produced in the gap between tetramers. The polarization of plasma resonant cavity revels that the morphology plays a decisive role in generating the hot spots, After changing both the combination mode of tetramer nanowires and the rotation angle of the four-prism, the local surface exciton resonance of the unrotated asymmetric tetramer structure is most ideal and has resonance intensity higher than the that of symmetrical four-prism structure. Therefore, our results provide a structural model and theoretical parameters for the enhancement of electric field intensity by local surface plasmon resonance effect.

Optical properties of a triple AlGaAs/GaAs quantum well purported for quantum cascade laser active region

A theoretical investigation on the conduction electron states in a triple inverse parabolic AlGaAs/GaAs quantum well, designed in the spirit of the active region for a quantum cascade laser, is performed. The study includes the influence of externally applied static electric and magnetic fields. The energy values and corresponding eigenfunctions are determined with the use of the effective mass approximation within the parabolic band description. The information on the allowed states is, then, used to evaluate some coefficients that represent the intraband nonlinear optical response of the structure. Numerical results are presented for the optical absorption and relative refractive index change coefficients as well as for those of nonlinear optical rectification and second harmonic generation. It is discussed that, in general, the amplitude and position of resonant peaks in the calculated quantities can be noticeably affected by the variation in the strength of the applied probe fields. Accordingly, the features of the investigated properties could suitably determine the application of this kind of structures for device proposals, as long as they can affect lasing regime in them.

Anomalous blueshift of aperture resonance enabled by the loss of a thin film

The substrate effects on aperture resonance have been widely studied because the resonance peak position is key for sensing, communications, and field enhancement applications. So far, the theoretical works have focused on the lossless infinite substrate case, which only explains the resonance peak redshift by the substrate index. The loss effect has not been investigated yet because lossy infinite substrate significantly reduces the aperture transmission. Therefore, this work studied the loss effect on aperture resonance via an analytic model of the transmission though slot antennas on a finite substrate. When the substrate thickness was very thin compared to the wavelength, the transmittance remained high even for a large imaginary part of the refractive index; furthermore, the developed model predicted a strong blueshift when this imaginary part exceeds the real part. Besides, the zero of the imaginary part of the coupling strength was crucial in determining the resonance frequency for both infinite and finite substrates. Thus, this study can contribute to the material characterization, label-free detection, and efficient design of active metamaterials.

Femtosecond-Laser-Induced Saturable Absorption and Optical Limiting of Hollow Silver Nanocubes: Implications for Optical Switching and Bioimaging

The effects of shape, size, and surface plasmon resonance (SPR) peak position (λSPR) on nonlinear absorption (NLA) were investigated at 808 nm, using a femtosecond laser. We found that NLA behavior is the result of competition between saturable absorption (SA) and reverse saturable absorption (RSA). SA behavior, i.e., optical transparency in silver nanocrystals, is introduced by the change in shape and structure from solid nanospheres to hollow nanocubes. For the latter, SA behavior dominates at low input irradiance, while RSA dominates at higher laser powers. A series of hollow silver nanocubes (HAgNCs) was synthesized that exhibit SPR peaks at 510, 550, 590, and 630 nm, hence named as HAgNC-510, HAgNC-550, HAgNC-590, and HAgNC-630, respectively. The edge lengths (l) of HAgNC-510, HAgNC-550, HAgNC-590, and HAgNC-630 were determined to be 33 ± 4, 45 ± 8, 70 ± 10, and 100 ± 15 nm. The switching of SA to RSA occurred at lower laser power for larger HAgNCs as compared to the smaller ones. The saturation intensity (Isat) was found to vary linearly with the size of HAgNCs. Moreover, for a four-times rise in input pulse intensity (63 → 252 GW/cm2), a huge increase of 3650% in the NLA coefficient, βeff, was observed for HAgNC-590, whereas merely 19% increase was found for the solid silver nanoparticles (SAgNP-400). The extraordinary enhancement in βeff is attributed to the enhanced electric field at the sharp edges and corners of the nanocubes. The red-tailing of SPR peaks also had a significant effect on the values of βeff. The outcomes, i.e., optical transparency and SA–RSA switching, will open vistas for a variety of diverse applications such as optical switching, limiting, and bioimaging.

Au–Pd core–shell nanoparticle film for optical detection of hydrogen gas

Hydrogen use, as a clean and almost infinite energy source, has an economic impact in many industries. The problem is that this gas cannot be used like any gas because of its explosiveness at 4% in the air, hence the need to know its concentration any time for security reasons. The permanent detection of hydrogen leaks is essential to monitor and to control the hydrogen concentration to prevent any possible risk. In our current research, we have developed hydrogen ultrasensitive sensors by depositing a thin film of Au–Pd core–shell nanoparticles (NPs) on a transparent glass substrate in order to detect hydrogen in its gaseous form. The colloidal Au–Pd core–shell NPs were synthesized according to a multi-reduction step method. The structural characterizations, the nature, and the density of Au–Pd core–shell NPs have been characterized by scanning electron microscopy and transmission electron microscopy. The morphology, size, and structure of Au–Pd core–shell NPs can be controlled under synthesis conditions. The size of the core–shell studied in this work is 13 nm for gold NP diameter and 0 nm–2.3 nm for palladium thicknesses. The physical properties of NPs, such as the optical absorbance response under hydrogen, strongly depend on the nature of the shell and the ratio between the core and the shell. At different hydrogen concentrations ranging from 1% to 4%, the optical response changes in the position of the surface plasmon resonance peak on the absorbance spectrum after the first loading/unloading hydrogen cycle.

Reverse design of microring resonator channel dropping filters

We present a reverse solving design approach to achieve accurate control over the response shapes and resonant peak positions of channel dropping filters implemented by coupled microring resonators. From performance to geometry, we obtain the geometric parameters based on the layout connecting multiple cells consisting of two straight waveguides and one microring in series to achieve the desired filter performance. We discuss the theoretical limit that the filters can reach and how to obtain the geometric parameters corresponding to the desired response reversely. Finally, the numerical simulations are carried out, and the results agree well with theoretical analysis, verifying the efficacy of our approach.

Relevant issues of periodic vibration monitoring of buildings and structures

Introduction. The author proposes a new universal optimization approach to mechanical safety monitoring of buildings and structures in the process of their operation. The new approach involves periodic monitoring of mechanic vibrations.&#x0D; Materials and methods. The methodology of periodic monitoring performable within the framework of general monitoring is based on the analysis of changes in the first natural frequency of a building or a structure and the logarithmic decrement of its damping along three mutually perpendicular axes. The shape and position of resonance peaks of the amplitude spectrum are employed to analyze resonant frequencies and logarithmic decrements of damping. The analysis of those electronically archived parameters is performed, whose values change over time proportionately with vibrations of a monitored facility. The time dependence of the first resonant frequency of a structure is considered as a generalized characteristic of its mechanical safety.&#x0D; Results. The author has shown that findings of the spectral analysis performed in respect of the vibration process are irrespective of a measurement method, provided that the uniformity of external influences is ensured. The frequency dependence of the structure’s first mode of vibrations on time (per year) has two non-linear sections within the entire term of operation. Following the analysis of measurements taken at construction facilities exposed to wind loads, it’s been found that advanced monitoring instruments can identify changes in the value of the first resonant frequency and the damping decrement with a reasonable degree of accuracy. The author believes that this finding has great practical importance.&#x0D; Conclusions. Identification of a trend towards a change in frequency and damping decrement values for the first mode of natural vibrations can help to schedule actions for the improvement of the mechanical safety of an engineering structure, and in some cases it can prevent an upcoming accident.

Tunable and Reconfigurable Dual-Band Chiral Metamirror

Chiral metasurfaces have recently undergone a dramatic development, due to their important applications in optics, chemistry and biology. However, the tunability and reconfigurability of the chiral metasurfaces remain challenges. Then, we proposed an S-shaped metamirror consisting of a MIM (Au-LiNbO3−Au) structure with a dual-band chiral absorption in the near-infrared range. The proposed structure has two resonant wavelengths with a giant chiro-optical effect. The giant chiro-optical effect originates from the different plasmonic resonances induced by the incident circularly polarized light (CPL) with opposite spin states. By tuning the voltage and thus tuning the refractive index of the lithium niobate (LiNbO3), chiral resonant wavelengths can be dynamically adjusted in a large range as desired. Furthermore, by tuning the refractive index of LiNbO3, we can move the short-wavelength resonance peak to the position of another long-wavelength resonance peak. Therefore, the chiral metamirror can be dynamically reconfigured at the position of the long-wavelength resonance peak. The work offers a further step in developing tunable and reconfigurable chirality for possible applications including reconfigurable chiral hologram, chiral-selective absorber and other chiral components in near-infrared region.

The Ettingshausen effect in doped semiconductor superlattice under the influence of confined optical phonon

The electron – optical phonon scattering is considered in detail to studying the Ettingshausen effect in doped semiconductor superlattice under the influence of phonon confinement and laser radiation. The analytical expressions for tensors and the Ettingshausen coefficient are obtained by using the kinetic equation method. The Ettingshausen coefficient depends on temperature of the sample, amplitude and frequency of laser radiation, magnetic field and the quantum number m specific for the confinement of phonon. The dependences are clearly displayed in the numerical results for GaAs:Be/GaAs:Si doped semiconductor superlattice. The magnetic field makes the Ettingshausen coefficient change in quantitative under the influence of temperature or laser amplitude and change the resonance condition. The numerical results show that both resonance condition and resonance peaks position are affected by the increase of quantum number m. We also get the result corresponding to the unconfined optical phonon case when m is set to zero. Due to the change of the wave function and energy spectrum of electrons, most of results for the Ettingshausen effect in doped semiconductor superlattice obtained are different from the case of bulk semiconductor. Moreover, in comparison with the case of unconfined optical phonon, under the influence of phonon confinement effect, the Ettingshausen coefficient changes in magnitude, the number and position of resonance peaks.

Synthesis and Multipole Plasmon Resonances of Spherical Aluminum Nanoparticles.

In comparison to Au and Ag, the high plasma frequency of Al allows multipole plasmon resonances from the ultraviolet to visible (UV-vis) range to be achieved by its nanoparticles with much smaller sizes and even a spherical shape. Herein, we report the high-supersaturation growth of monodisperse spherical Al nanoparticles (Al NPs) from 84 to 200 nm and their distinctive size-dependent multipole plasmon resonance properties in the UV-vis range. Linear relationships between the particle diameter and resonance peak positions of the dipole, quadrupole, and octupole were observed experimentally and confirmed by finite-difference time-domain (FDTD) calculations. FDTD calculations further reveal the high scattering-to-extinction ratio of multipole modes for the particle diameters >100 nm. The extinction coefficients of spherical Al NPs with different diameters were also determined. The excellent matching between the experimental and simulated results in the present work not only offers a standard for the synthesis and characterization of high-quality Al NPs but also provides new insight into the multipole plasmonic properties of Al NPs for advanced optical and sensing applications.

Electron-related nonlinear optical properties of cylindrical quantum dot with the Rosen–Morse axial potential

We present a theoretical study on the effects of intense laser field (ILF) and static electric field on the linear and nonlinear optical properties of a cylindrical quantum dot with Rosen–Morse axial potential under the framework of effective mass and parabolic band approximations. This study also takes into account the effects of the structure parameters (η, V1, and R). The analytical expressions of the linear, third-order nonlinear and total optical absorption coefficients (TOACs) and the relative refractive index changes (RRICs) are obtained by using the compact-density-matrix approach. The results of numerical calculations show that the resonant peak position of the TOACs and RRICs shifts towards lower energies and the magnitude of the peak increases with the effect of the static electric field and ILF. In addition, it is observed that while the resonant energies of the TOACs and RRICs of system shift towards the higher (lower) energies with the enhancement of η, V1, they decrease with the augmentation of R. Thus, the findings of this study show that the optical properties of the structure can be adjusted by changing the magnitude of structure parameters and applied external fields.

Coherent electron quantum transport in hbox {In}_{0.53}hbox {Ga}_{0.47}As/GaAs_{0.51}hbox {Sb}_{0.49} double barrier resonant tunnelling structures

In this work, we have modelled and computed the transport properties of the double-barrier InGaAs/GaAsSb structure from the resonant tunnelling point of view. Based on the classical Tsu-Esaki formula for the tunnelling current, we have calculated the current density-voltage characteristic of a Al-free type-II hbox {In}_{0.53}hbox {Ga}_{0.47}hbox {As/GaAs}_{0.51}hbox {Sb}_{0.49} structure at different cryogenic and elevated temperatures. The tunnelling coefficient has been calculated in the framework of effective mass approximation with nonparabolicity included, using the transfer matrix approach. A good qualitative agreement of the position of resonant current peaks with the existing experimental data was achieved. Our calculation shows a very high sensitivity of the tunnelling current peak on monolayer-scale layer structure fluctuation which strongly affects peak to valley ratio in the resonant tunnelling structure.

Dynamics of instability in plasmonic response of nanostructured gold thin films on ambient ageing

Instability in the plasmonic response of nanostructured gold (Au) thin films on ambient ageing has been investigated. Different types of Au nanostructures (island, percolated, and continuous thin film) are obtained at the early stage of thin film growth by variation in film thickness using sputtering technique. Absorbance spectra of as-deposited island Au film shows a systematic blue-shift in the localized surface plasmon resonance (LSPR) peak position on ageing. The rate of blue-shift in the LSPR peak position is fitted with single-exponential decay function to analyse the dynamics of the plasmonic response. The as-deposited percolated Au film displays a transformation of broadened plasmonic response into a wavelength independent absorbance profile on ageing. The immersion of a new plasmonic band in the absorbance spectra is noted for continuous Au thin film on ageing. The change in plasmonic responses of nanostructured Au thin films on ambient ageing is found to be directly correlated with the re-organization of the surface morphology. Finally, ageing-induced solid-state dewetting and crystallization are found to be the main responsible processes of the underlying mechanism for morphological re-organizations, leading to change in the plasmonic response of the nanostructured Au thin films.