Resonant Excitation Research Articles

Laterally Excited Resonators Based on Single-Crystalline LiTaO3 Thin Film for High-Frequency Applications

High-performance acoustic resonators based on single-crystalline piezoelectric thin films have great potential in wireless communication applications. This paper presents the modeling, fabrication, and characterization of laterally excited bulk resonators (XBARs) utilizing the suspended ultra-thin (~420 nm) LiTaO3 (LT, with 42° YX-cut) film. The finite element analysis (FEA) was performed to model the LT-based XBARs precisely and to gain further insight into the physical behaviors of the acoustic waves and the loss mechanisms. In addition, the temperature response of the devices was numerically calculated, showing relatively low temperature coefficients of frequency (TCF) of ~−38 ppm/K for the primary resonant mode. The LT-based XBARs were fabricated and characterized, which presents a multi-resonant mode over a wide frequency range (0.1~10 GHz). For the primary resonance around 4.1 GHz, the fabricated devices exhibited a high-quality factor (Bode-Q) ~ 600 and piezoelectric coupling (kt2) ~ 2.84%, while the higher-harmonic showed a greater value of kt2 ~ 3.49%. To lower the resonant frequency of the resonator, the thin SiO2 film (~20 nm) was sputtered on the suspended device, which created a frequency offset between the series and shunt resonators. Finally, a ladder-type narrow band filter employing five XBARs was developed and characterized. This work effectively demonstrates the performance and application potential of micro-acoustic resonators employing high-quality LT films.

Fabry-Perot and Tamm modes hybridization in spatially non-homogeneous magneto-photonic crystal

We presented the results of studying the features of various resonant modes excitation in a spatially non-homogeneous magnetophotonic crystal with a plasmonic coating. It has been shown that in a such crystal several resonant Fabry-Perot modes and the Tamm plasmon mode are generated at once, which undergo a spectral shift inside the photonic bandgap when the thicknesses of the optical and magnetic layers of magnetophotonic crystal is change.

Robust single modified divacancy color centers in 4H-SiC under resonant excitation

Color centers in silicon carbide (SiC) offer exciting possibilities for quantum information processing. However, the challenge of ionization during optical manipulation leads to charge variations, hampering the efficacy of spin-photon interfaces. Recent research predicted that modified divacancy color centers can stabilize their charge states, resisting photoionization. This study presents a method for precisely creating single divacancy arrays in 4H-SiC using a focused helium ion beam. Photoluminescence tests reveal consistent emission with minimal linewidth fluctuations (∼50 MHz over 3 h). By measuring the ionization rate for different polytypes of divacancies, we found that the modified divacancies are more robust against resonant excitation. Furthermore, angle-resolved photoluminescence excitation spectra unveil two resonant-transition lines with orthogonal polarizations. Enhanced optical and spin characteristics were notably observed in these color centers compared to those generated through carbon-ion and shallow implantation methods, positioning modified divacancies as promising contenders for advancing quantum networking.

Relaxation Channels of Two Types of Hot Carriers in Gold Nanostructures.

A fundamental understanding of hot carrier relaxation in metal nanostructures is essential for realizing their application potential in energy conversion and photocatalysis. Despite previous investigations of the relaxation of hot carriers generated by surface plasmon resonance (SPR) excitation and interband transitions (IBTs), the hot carrier relaxation lifetimes and their associated mechanisms remain unclear. Herein, we demonstrate two distinct hot carrier relaxation channels in gold plasmonic nanostructures. The experimental observations reveal that the hot carrier relaxation is faster following SPR excitation than that from IBTs in gold nanoparticles and nanorods. The experimental results and theoretical calculations indicate that the numerous plasmon-induced hot carriers undergo surface-mediated carrier-carrier scattering in large gold nanostructures, whereas almost all IBT-induced hot carriers experience bulk carrier-carrier scattering. These findings advance our understanding of hot carrier relaxation and contribute to a clearer microscopic description of scattering channels in plasmonic nanostructures.

Quasinormal mode expansion in thin elastic plates

Elastic wave manipulation using large arrays of resonators is driving the need for advanced simulation and optimization methods. To address this we introduce and explore a robust framework for wave control: quasinormal modes (QNMs). Specifically, we consider the problem for thin elastic plates, where the Green's function formalism is well known and readily exploited to solve multiple scattering problems. By studying the associated nonlinear eigenvalue problem we derive a dispersive QNM expansion, providing a reduced-order model for efficient forced response computations which reveals physical insight into the resonant mode excitation. Furthermore, we derive eigenvalue sensitivities with respect to resonator parameters and apply a gradient-based optimization to design quasi-bound states in the continuum and position eigenfrequencies precisely in the complex plane. Scattering simulations validate our approach in structures such as graded line arrays and quasicrystals. Drawing on QNM concepts from electromagnetism we demonstrate significant advances in elastic metamaterials, highlighting their potential for tailored wave manipulation. Published by the American Physical Society 2024

Floquet engineering of anomalous Hall effects in monolayer MoS2

Light-matter interactions have emerged as a new research focus recently offering promises of unveiling novel physics and leading to applications under nonequilibrium conditions. The quantized Hall conductivities predicted by Floquet theory assuming a Fermi-Dirac distribution however deviate from experimental observations. To resolve these puzzles, we consider the effect of nonequilibrium electron occupation to study the anomalous, valley, and spin Hall effects of a prototype monolayer transition metal dichalcogenide MoS2. We find that spin Hall conductivity can be effectively suppressed approaching zero value by linearly polarized light under near resonant excitations. In contrast, it is substantially enhanced by circularly polarized light, originating from optical selection rules and topological phase transitions. Besides, the quantized anomalous Hall conductivity is much reduced if nonequilibrium occupations of Floquet bands are considered. Our study provides a novel avenue for engineering various Hall effects in two-dimensional materials using light, holding great promises for future device applications.

A Laterally Excited Bulk Acoustic Wave Resonator Based on LiNbO3 with Arc-Shaped Electrodes.

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO3 thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO3 thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO3 thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance.

External-cavity diode laser at 2.6 µm and its frequency stabilization with a scanning Fabry-Pérot cavity

We report on the construction of an external cavity diode laser at 2.6 µm wavelength and its frequency stabilization with an external scanning Fabry-Pérot cavity using Pound-Drever-Hall (PDH) frequency stabilization technique. We discuss the frequency noise characteristics of the laser using the PDH residual error signal analysis and the locking performance. We have achieved a 2.5 x 105 suppression factor in the frequency noise power spectral density at Fourier frequencies lower than 100 Hz when the laser is stabilized. The laser is employed to observe resonant excitation on the 5s5p3P0 →5s4d3D1 transition in cold 88Sr atoms trapped in a magneto-optical trap. We have observed an enhancement in the trapped atom number by a factor of 8.3 compared to the case when a single laser at 707 nm is employed for repumping.

Spin-photon entanglement with direct photon emission in the telecom C-band

Quantum networks, relying on the distribution of quantum entanglement between remote locations, have the potential to transform quantum computation and secure long-distance quantum communication. However, a fundamental ingredient for fibre-based implementations of such networks, namely entanglement between a single spin and a photon directly emitted at telecom wavelengths, has been unattainable so far. Here, we use a negatively charged exciton in an InAs/InP quantum dot to implement an optically active spin qubit taking advantage of the lowest-loss transmission window, the telecom C-band. We investigate the coherent interactions of the spin-qubit system under resonant excitation, demonstrating high fidelity spin initialisation and coherent control using picosecond pulses. We further use these tools to measure the coherence of a single, undisturbed electron spin in our system. Finally, we demonstrate spin-photon entanglement in a solid-state system with entanglement fidelity F = 80.07 ± 2.9%, more than 10 standard deviations above the classical limit.

Spectral Flux Enhancement of X Rays for Addressing Ultranarrow Nuclear Transitions.

Recently, the 1.4 feV ultranarrow nuclear transition at 12.4keV energy in ^{45}Sc was resonantly excited for the first time using radiation from the self-seeded EuXFEL laser [Y. Shvyd'ko et al., Resonant x-ray excitation of the nuclear clock isomer ^{45}Sc, Nature (London) 622, 471 (2023)NATUAS0028-083610.1038/s41586-023-06491-w], establishing ^{45}Sc as a promising candidate for a future Mössbauer nuclear clock. While this experiment demonstrated a high potential of x-ray free-electron laser sources for resonantly exciting nuclear isomers in the hard x-ray range, it also highlighted a severe limitation in the achievable excitation level caused by their extremely large spectral bandwidth ∼1 eV. In this Letter, we propose a method to enhance the spectral flux of x-ray free-electron laser radiation using a resonant absorber with a longitudinal gradient in the nuclear transition frequency. A portion of the incident pulse can be absorbed into a nuclear collective excitation, and converted back into x-ray radiation by reversing the sign of the frequency gradient. Spectral narrowing and flux enhancement of this re-emitted x-ray field is achieved by using a reversed frequency gradient with a smaller magnitude than the initial one. About a hundredfold of such spectral flux enhancement is feasible in ^{45}Sc_{2}O_{3} single crystal, rendering a more efficient source for nuclear excitation and facilitating the experimental observation of resonant fluorescence and coherent forward scattering at the 12.4keV transition, both of which are essential for realizing a nuclear clock.

Resonant Excitation of Kelvin Waves by Interactions of Subtropical Rossby Waves and the Zonal Mean Flow

Abstract Equatorial Kelvin waves can be affected by subtropical Rossby wave dynamics. Previous research has demonstrated the Kelvin wave growth in response to subtropical forcing and the resonant growth due to eddy momentum flux convergence. However, the relative importance of the wave–mean flow and wave–wave interactions for the Kelvin wave growth compared to the direct wave excitation by the external forcing has not been made clear. This study demonstrates the resonant Kelvin wave excitation by interactions of subtropical Rossby waves and the mean flow using a spherical shallow-water model. The use of Hough harmonics as basis functions makes Rossby and Kelvin waves prognostic variables of the model and allows the quantification of terms contributing to their tendencies in physical and wave spaces. The simulations show that Kelvin waves are resonantly excited by interactions of Rossby waves and the balanced zonal mean flow in the subtropics, provided the Rossby and Kelvin wave frequencies, which are modified by the mean flow, match. The resonance mechanism is substantiated by analytical expressions. The Kelvin wave tendencies are caused by velocity and depth tendencies: The velocity tendencies due to the meridional advection of the zonal mean velocity can be outweighed by the zonal advection of the Rossby wave velocity or by the depth tendencies due to Rossby wave divergence. Identifying the resonant excitation mechanism in data should contribute to the quantification of Kelvin wave variability originating in the subtropics. Significance Statement This study seeks to understand how Kelvin waves, which are eastward-propagating disturbances in the tropical atmosphere, are connected to Rossby wave dynamics in the subtropics. Using idealized simulations, the Kelvin wave excitation is explained as a resonance effect due to interactions of Rossby waves and the zonal mean flow. The mechanism contributes to the understanding of atmospheric wave interactions and extratropical effects on the tropics. Further work searching for evidence of the new mechanism in atmospheric data may shed a new light on subseasonal variability in the tropics, such as the Madden–Julian oscillation.

Measurement of temporal evolution of antiferromagnetic domain change in nickel oxide driven by 2TO phonon mode excitation via pump-probe experiment

The temporal evolution of antiferromagnetic domain pattern changes under resonant excitation of the second-order transverse optical phonon mode in nickel oxide was investigated using mid-infrared free electron laser (MIR-FEL) pulses and visible nanosecond probe laser pulses at room temperature. We visualized the domain patterns through magneto-optical polarized microscopy in transmission and observed their temporal variation after the phonon excitation via MIR-FEL. We evaluated the differences throughout the timeline using the structural similarity index measure technique from domain images with and without MIR-FEL irradiation. We found that the MIR-FEL irradiation induces significant structural changes in the domain patterns. The maximum difference was observed at the timing of the MIR-FEL irradiation and exponentially recovered with the time constant of 1.4 ± 0.2 ms. This rather long-time constant could be owing to the spin relaxation, whilst further investigation is needed to confirm the underlying mechanism.

Magneto-optical Goos–Hänchen shift in uniaxial anisotropic epsilon-near-zero metamaterials

Abstract We theoretically investigate the enhancement of the magneto-optical Goos-Hänchen (MOGH) shift in multilayer structure combining uniaxially anisotropic epsilon-near-zero (ENZ) metamaterials with magneto-optical (MO) materials. The structure enables the excitation of magneto-optical surface plasmon resonance (MOSPR) without the need for a prism or grating coupler, thereby achieving a significant enhancement of the MOGH shift. The effect of the thickness of the ENZ layer and the type of magnetic metal in this structure on the MOGH shift is also discussed. Based on the above structure, we design a high-sensitivity miniature biosensor that is used for the detection of hemoglobin concentration in human blood. The maximum sensitivity achievable with this sensor is 1.4×106 λ/RIU. The results of this investigation contribute to the development of biosensors towards miniaturization and integration.

Measurement of differential collisional excitation cross sections for the Kα emission of He-like oxygen

We measure the energy-differential cross sections for collisional excitation of the soft x-ray electric-dipole Kα (x+y+w) emission from He-like oxygen (O ), using an electron beam ion trap. Values near their excitation thresholds were extracted from the observed emissivity by rapidly cycling the energy of the exciting electron beam. This allows us to subtract time-dependent contributions of the forbidden z-line emission to the multiplet. We develop a time-dependent collisional-radiative model to further demonstrate the method and predict all spectral features. We then compare the extracted x+y+w cross sections with calculations based on distorted-wave and R-matrix methods from the literature and our own predictions using the . All R-matrix results are validated by our measurements of direct and resonant excitation, supporting the use of such state-of-the-art codes for astrophysical and plasma physics diagnostics. Published by the American Physical Society 2024

Reusable SERS Platform of Femtosecond Laser Processed Substrate for Detection of Malachite Green.

This study presents the development of highly efficient Surface-Enhanced Raman Scattering (SERS) substrates through femtosecond (fs) laser processing of crystalline silicon (Si), resulting in mountain-like microstructures. These microstructures, when decorated with gold nanoparticles (Au NPs), exhibit remarkable SERS performance due to the creation of concentrated hotspots. The enhanced Raman signals originate from the excitation of localized surface plasmon resonance (LSPR) of the Au NPs and the multi-scale rough morphology of the Si substrates. Finite-element method simulations confirm the electromagnetic field enhancement in narrow gaps, supporting the experimental observations. The fabricated substrates show high uniformity, oxidation resistance, long-term stability, and exceptional reproducibility, making them ideal for molecular detection, especially in food safety applications. A remarkable enhancement factor (EF) of 1010 is attained in the detection of Malachite Green (MG), boasting a limit of detection (LoD) as low as 10-14 M. This underscores the immense potential of this technique for achieving highly sensitive and dependable SERS-based sensing capabilities.

Femto-Laser Processed Metasurface With Fano Response: Applications to a High Performance Refractometric Sensor

The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs. We have engraved a split grating geometry on stainless steel using femtosecond laser processing. This structure serves as a template to fabricate efficient plasmonic sensors, where a thick gold layer is grown conformally on it. The scanning electron microscope (SEM) images confirm the generation of the split laser-induced periodic spatial structures. The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances (SPRs) at two different wavelengths. Furthermore, the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance. Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure. The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction. The parameters extracted from the fitting, such as the resonance wavelengths and line widths, are used to evaluate the performance of our device as a refractometric sensor for liquids. The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU−1, respectively. Besides the compact design of our sensing device, its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup.

Control resonant excitation of surface plasmon polariton in quantum-dot molecule system via tunneling induced transparency and Autler–Townes splitting

Electromagnetic induced transparency (EIT) and Autler–Townes splitting (ATS) both produce a transparency window in an absorption profile, yet EIT is distinct in that it can create a transparency window for a weak control field. To elucidate the distinct physical mechanisms underlying EIT and ATS effects, we explore the controlled resonant excitation of surface plasmon polaritons (SPPs) within these regimes. Our setup is composed of three layers: a top vacuum or air layer, a central metal film, and a bottom layer of dielectric medium based on the quantum-dot molecules (QDMs) system. Unlike typical systems, that employ prism or grating coupling scheme, our setup takes advantage of the unique features of the QDMs medium to investigate the direct resonance excitation of SPPs. A weak probe and a strong control field are carried through air or vacuum to the top layer. Our results demonstrate that the permittivity of the bottom medium displays tunneling induced transparency (TIT) if the tunneling strength (Te) and the decay rate of the direct exciton (Γ1) follow the condition Te/Γ1⩽0.5; otherwise, it represents the ATS effect. In both instances, the permittivity of the QDMs medium satisfy the low-loss (high transmission) criteria, i.e., Re [ɛd]<1 and Im [ɛd]≪1, providing a framework for exploring the control resonant excitation of SPPs. We simulate the reflection and transmission spectra using the Fresnel’s formula and noticed sharp dips in reflection and peaks in the transmission spectra, which are the signature of coupler free resonance excitation of SPPs. We noticed that the narrow peak in TIT allows for strong light transmission and thus a high peak in SPP resonance excitation, resulting in higher sensitivity in plasmonic sensors. Conversely, the large spacing between the two peaks in the ATS effect broadens the range of effective excitation frequencies for SPPs, increasing the system’s adaptability and efficiency in applications requiring broad spectrum responses.

Observation of molecular resonant double-core excitation driven by intense X-ray pulses

The ultrashort and intense pulses of X-rays produced at X-ray free electron lasers (XFELs) have enabled unique experiments on the atomic level structure and dynamics of matter, with time-resolved studies permitted in the femto- and attosecond regimes. To fully exploit them, it is paramount to obtain a comprehensive understanding of the complex nonlinear interactions that can occur at such extreme X-ray intensities. Herein, we report on the experimental observation of a resonant double-core excitation scheme in N2, where two 1σ core-level electrons are resonantly promoted to unoccupied 1πg*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1{\\pi }_{g}^{* }$$\\end{document} molecular orbitals by a single few-femtosecond broad-bandwidth XFEL pulse. The production of these neutral two-site double core hole states is evidenced through their characteristic decay channels, which are observed in good agreement with high-level theoretical calculations. Such multi-core excitation schemes, benefiting from the high interaction cross sections and state- and site-selective nature of resonant X-ray interactions, should be generally accessible in XFEL irradiated molecules, and provide interesting opportunities for chemical analysis and for monitoring ultrafast dynamic processes.

On the Origin of Signal and Bandwidth of Converse Magnetoelectric Magnetic Field Sensors

AbstractConverse magnetoelectric sensors enable the detection of low‐frequency and low‐amplitude magnetic fields over a bandwidth of several kilohertz by combining the electrical excitation of a magnetoelectric resonator via a piezoelectric layer with an inductive readout. Here, a comprehensive sensor model is presented to further foster the development of this promising sensor concept. The model relates the output signal to the device characteristics, taking into account the magnetoelastic and electromechanical properties, the resonator geometry, and operating conditions. The sensor system is thoroughly experimentally analyzed to validate the model. Based on the analysis, the sensor concept is explained in detail, including the origin of its loss and bandwidth and their connection with the magneto‐mechanical loss in the magnetostrictive layer. Significant advances have been made in the comprehensive understanding of converse magnetoelectric sensors, providing a solid basis for future improvements in magnetoelectric sensor systems.

Impact of block-loading on the high cycle fatigue strength of superalloy 617M at 973 K

The study demonstrates the positive influence of coaxing on the fatigue strength of alloy 617M under high cycle fatigue (HCF) loading at stress ratio (R) − 1, frequency ≈ 85 Hz, and temperature of 973 K. Tests were performed employing resonance excitation in two patterns viz., constant amplitude loading and block loading using a ‘low-to-high’ pattern. The fatigue limit for the constant amplitude loading pattern was determined to be 320 MPa for a runout criterion of 108 cycles. Upon under-stressing the alloy by application of a block loading pattern, the limit increased to 335 MPa. The increase of stiffness and associated resonance frequency during cycling indicated an initial hardening regime brought about by work hardening followed by a period of secondary hardening owing to precipitations occurring in the matrix. In the later stage, the frequency response also indicated the influence of dynamic strain ageing (DSA) on the alloy behaviour. Comparative microstructural characterisation of specimens is conducted to extend the understanding of coaxing and the resulting changes occurring in the work-hardening behaviour of the alloy.