Resonant Excitation Research Articles

Giant Light Emission Enhancement in Strain-Engineered InSe/MS2 (M = Mo or W) van der Waals Heterostructures.

Two-dimensional (2D) heterostructures (HSs) offer unlimited possibilities for playing with layer number, order, and twist angle. The realization of high-performance optoelectronic devices, however, requires the achievement of specific band alignments, k-space matching between conduction and valence band extrema, and efficient charge transfer between the constituent layers. Fine-tuning mechanisms to design ideal HSs are lacking. Here, we show that layer-selective strain engineering can be exploited as an extra degree of freedom to tailor the band alignment and optical properties of 2D HSs. To that end, strain is selectively applied to MS2 (M = Mo or W) monolayers in InSe/MS2 HSs, triggering a giant photoluminescence enhancement of the highly tunable but weakly emitting InSe of up to >2 orders of magnitude. Resonant excitation measurements, supported by first-principles calculations, provide evidence of a strain-activated charge transfer from the MS2 monolayers toward InSe. The huge emission enhancement of InSe widens its range of applications for optoelectronics.

Evolution characteristics and mechanism of coal fracture under resonance excitation based on computed tomography scanning

AbstractThe resonance of coal reservoir induced by external excitation is a kind of environment‐friendly stimulation technology. In this work, an experimental system was established to carry out the coal resonance fracturing experiments, and the change trend of fracture structure was investigated by computed tomography scanning. The results showed that under the excitation of vibration within the resonance frequency band range, the coal fracture will gradually expand to failure. There are three forms of coal fracture expansion under the condition of resonant, which are the formation of slip zones in coal, the formation of fracture at phase interface and the formation of ‘void’. When the excitation frequency is constant, the natural frequency of coal decreases gradually with the expansion of fractures, resulting in the vibration frequency gradually deviating from the natural frequency of coal, and the fracture propagation behaviour of vibrating coal gradually changes from divergence to convergence.

Resonant excitation of whistler wave via Cherenkov emission by sweeping radio frequency heated hot spot across the equatorial electrojet

A new and efficient scheme of resonant excitation of whistlers via Cherenkov emission in an equatorial electrojet by sweeping the heater in phase with the desired mode is investigated. The equatorial ionosphere around the maximum electron density, at a height of ∼100 km, is a suitable ionosphere duct for guided propagation of very low frequency whistler waves over long distances. This ionosphere duct also has a horizontal electrojet current across the ambient magnetic field. A ground-based high-gain, high-power radio frequency antenna array with a frequency of around 3.7 MHz can locally heat the ionosphere and modify the electrojet, and a hot spot is generated. By sweeping the hot spot along the magnetic field at the phase velocity of a whistler, one can resonantly excite the whistler wave via Cherenkov emission. These whistlers can trap and accelerate the charged particles to very high energies in the ionosphere.

Surface plasmon resonance excitation and imaging in circular gratings: a study of non-polarized, radial and azimuthal polarization effects

Abstract This study explores the effects of various polarization states on Surface Plasmon Resonance (SPR) in circular gratings, emphasizing their potential in sensing technologies. We present a mathematical modeling framework alongside experimental investigations involving the fabrication and characterization of circular gratings using linearly polarized, radially polarized, and non-polarized light. Our findings demonstrate stable SPR responses across multiple polarization angles, with strong signals achievable even with non-polarized light, minimizing reliance on polarizers. Additionally, we analyze spatial intensity responses and the influence of polarization on excitation patterns, enhancing our understanding of plasmonic interactions. Through Surface Plasmon Resonance imaging (SPRi), we highlight the capability to capture topographical information, further contributing to advancements in plasmonics and the development of improved sensing devices.

Photo-induced chirality in a nonchiral crystal.

Chirality, a pervasive form of symmetry, is intimately connected to the physical properties of solids, as well as the chemical and biological activity of molecular systems. However, inducing chirality in a nonchiral material is challenging because this requires that all mirrors and all roto-inversions be simultaneously broken. Here, we show that chirality of either handedness can be induced in the nonchiral piezoelectric material boron phosphate (BPO4) by irradiation with terahertz pulses. Resonant excitation of either one of two orthogonal, degenerate vibrational modes determines the sign of the induced chiral order parameter. The optical activity of the photo-induced phases is comparable to the static value of prototypical chiral α-quartz. Our findings offer new prospects for the control of out-of-equilibrium quantum phenomena in complex materials.

Artificial Fine-Tuned van Hove Singularity in Twisted Bilayer and Double-Twist Trilayer Graphene with Enhanced Absorption for Photodetection and Photoemission in the Near-Infrared II Range.

Optical responses of twisted bilayer graphene at targeted wavelengths can be amplified by leveraging energy levels of van Hove singularities (VHS) via tuning periods of moiré superlattices. Therefore, precise control of twist angles as well as the moiré superlattices is necessary for fabricating integrated optoelectronic devices such as photodetectors and emitters. Although recent advances in twist angle control help the observation of correlated states in twisted magic-angle graphene structures, the impact of such precise control on enhanced optical absorption is still under investigation. Here, we employ a cut and stack method to construct tBLG with twist angles finely tuned between 4.6° and 6.6°, aligning the VHS near the telecom band with optimized optical absorption. The effective enhanced optical absorption and interlayer interaction uniformity are confirmed through Raman and reflection contrast spectroscopy. Additionally, we demonstrate increased photodetection responsivity and broadband upconversion photothermal emission, both enhanced by VHS, under resonant laser excitation. The study further explores a double-twist trilayer graphene configuration, resulting in better enhanced absorption due to the generation of additional VHS points. Our results underscore the potential of precisely engineered twisted structures in advancing the performance of optoelectronic devices.

ANALYSIS METHODS LABORATORY VIBRATION TESTING OF FLIGHT APPARATUS UNMANNED AVIATION COMPLEXES

The work examines the most well-known methods of vibration testing of unmanned aircraft systems. The simplest to implement vibration tests are the methods based on the sinusoidal vibration test method. The method of testing for the influence of broadband random vibration, during which several forms of natural oscillations of the structure are excited at the same time, is considered, which makes it possible to conduct vibration tests closer to the conditions of real operation. In addition, modeling of the statistical nature of vibration provides an opportunity to detect all effects of mechanical interaction of various structural elements and ensures the shortest duration of tests. Disadvantages of broadband random vibration tests include the high cost and complexity of the necessary equipment, as well as the high labor intensity of testing. The variable mode of narrow-band random vibration is considered, which is intermediate between the mode of wide-band random vibration and the mode with a variable sinusoidal signal. Systems that reproduce random narrowband vibration are less expensive and allow to simulate broadband vibration. The main disadvantage of the test when excited by a narrow-band spectrum is a slow change in the average frequency of the spectrum, which leads to the excitation of successive resonances of the tested product, while in the case of excitation by a wide-band spectrum, these resonances occur simultaneously. In addition, the duration of tests increases. The conducted comparative analysis made it possible to find out the conditions for the appropriate use of each considered method. The choice of the optimal method of vibration testing depends on the type of unmanned aircraft systems submitted for testing, the amount of information about it, the conditions of testing and further operation, as well as the possibility of implementing the loads defined in the method on the vibration testing equipment.

Excitation of ULF, ELF, and VLF Resonator and Waveguide Oscillations in the Earth–Atmosphere–Ionosphere System by Lightning Current Sources Connected with Hunga Tonga Volcano Eruption

The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, including ultra low frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) ranges. The electric current source due to lightning near the location of the Hunga Tonga volcano eruption has a wide-band frequency spectrum determined in this paper based on a data-driven approach. The spectrum is monotonous in the VLF range but has many significant details at the lower frequencies (ULF, ELF). The decreasing amplitude tendency is maintained at frequencies exceeding 0.1 Hz. The density of effective lightning current in the ULF range reaches the value of the order of 10−7 A/m2. A combined dynamic/quasi-stationary method has been developed to simulate ULF penetration through the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system. This method is suitable for the ULF range down to 10−4 Hz. The electromagnetic field is determined from the dynamics in the ionosphere and from a quasi-stationary approach in the atmosphere, considering not only the electric component but also the magnetic one. An analytical/numerical method has been developed to investigate the excitation of the global Schumann resonator and the eigenmodes of the coupled Schumann and ionospheric Alfvén resonators in the ELF range and the eigenmodes of the Earth–ionosphere waveguide in the VLF range. A complex dispersion equation for the corresponding disturbances is derived. It is shown that oscillations at the first resonance frequency in the Schumann resonator can simultaneously cause noticeable excitation of the local ionospheric Alfvén resonator, whose parameters depend on the angle between the geomagnetic field and the vertical direction. VLF propagation is possible over distances of 3000–10,000 km in the waveguide Earth–ionosphere. The results of simulations are compared with the published experimental data.

Static and dynamic Raman excitation mapping of chirality-pure carbon nanotube films

Raman spectroscopy is a powerful method for probing electronic and vibrational properties of materials, particularly nanomaterials such as single-wall carbon nanotubes. Typically, Raman spectroscopy is conducted at a single, or few, excitation wavelengths, but that provides limited information about excitation resonance structure, and their dynamical evolution. Here, we extend a sensitive full-spectrum technique to rapidly obtain two-dimensional Raman excitation maps both statically and dynamically for chirality-pure single-wall carbon nanotube films. We demonstrate sensitive evaluation of structured resonance profiles even from weak vibrational modes, and sub-second time resolution of the dynamics of photo-driven defect production. Findings include the direct observation of bands and their profiles – including bands which could be missed in conventional Raman spectroscopy - and demonstration of differences for odd vs. even defect band combinations. This opens up possibilities to investigate the coupling of electronic states with vibrational modes in nanomaterials and track their dynamical evolution subject to intentional modulation.

Research on coupling excitation and detection of capillary microcavity resonance

Research on coupling excitation and detection of capillary microcavity resonance

K-Resolved Ultrafast Light-Induced Band Renormalization in Monolayer WS2 on Graphene.

Understanding and controlling the electronic properties of two-dimensional materials are crucial for their potential applications in nano- and optoelectronics. Monolayer transition metal dichalcogenides have garnered significant interest due to their strong light-matter interaction and extreme sensitivity of the band structure to the presence of photogenerated electron-hole pairs. In this study, we investigate the transient electronic structure of monolayer WS2 on a graphene substrate after resonant excitation of the A-exciton using time- and angle-resolved photoemission spectroscopy. We observe a pronounced band structure renormalization, including a substantial reduction of the transient band gap in good quantitative agreement with our ab initio theory, revealing the importance of both intrinsic WS2 and extrinsic substrate contributions. Our findings deepen the fundamental understanding of band structure dynamics in two-dimensional materials and offer valuable insights for the development of novel electronic and optoelectronic devices based on monolayer TMDs and their heterostructures with graphene.

Terahertz wave generation via difference frequency mixing under nearly resonant exciton excitation with 1.5 μm band laser light in GaSb/AlGaSb multiple quantum wells

Abstract Direct conversion of 1.5-µm band light to terahertz wave is significant for ultrafast telecommunication and safer spectroscopy. This study reports generating terahertz waves via difference frequency mixing by exciting strained semiconductor quantum wells with a 1.5-µm band laser emitting two wavelengths. The excitation power dependence demonstrates a clear square dependence of the intensity, and the well-width dependence suggests the possibility creating nonlinear polarization by localized excitons.

Comparative study of electron transport through aromatic molecules on gold nanoparticles: insights from soft X-ray spectroscopy of condensed nanoparticle films versus flat monolayer films.

Understanding electron transport in self-assembled monolayers on metal nanoparticles (NPs) is crucial for developing NP-based nanodevices. This study investigates ultrafast electron transport through aromatic molecules on NP surfaces via resonant Auger electron spectroscopy (RAES) with a core-hole-clock (CHC) approach. Aromatic molecule-coated Au NPs are deposited to form condensed NP films, and flat monolayers are prepared for comparison. Soft X-ray techniques, including X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy, confirm oriented monolayers in both NP and flat films. The nuclear dynamics is studied via ion yield measurements. After subtracting secondary processes, the ion yield spectra of the condensed NP films reveal site-selective desorption of the methyl ester group by resonant core excitation. The ultrafast electron transport time from the carbonyl group through the phenyl rings to the metal surfaces in the condensed NP films is successfully determined via the RAES-CHC approach by subtracting inelastic scattering components. The chain length of the aromatic molecules influence the electron transport time in the NP films, reflecting the trends observed in the flat films. This evidence supports ultrafast electron transport via the through-bond model, independent of interactions between the molecules adsorbed on an NP itself or adjacent NPs. Identifying and subtracting background spectral components of the condensed NP films allows accurate analysis of the ultrafast dynamics. This study suggests that insights gained from electron transport processes in the flat monolayer films can be extrapolated to practical NP-molecule interfaces, providing valuable insights for the molecular design of NP-based devices.

The Impact of Silver Codoping on Tb3+ Luminescence in Lithium Tetraborate Glasses.

Spectroscopic properties of Tb-doped and Tb-Ag codoped lithium tetraborate (LTB) glasses with Li2B4O7 (or Li2O-2B2O3) composition are investigated and analysed using electron paramagnetic resonance (EPR), optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectra, PL decay kinetics and absolute quantum yield (QY) measurements. PL spectra of the investigated glasses show numerous narrow emission bands corresponding to the 5D4 → 7FJ (J = 6-0) and 5D3 → 7FJ (J = 5-3) transitions of Tb3+ (4f8) ions. The most intense PL band of Tb3+ ions at 541 nm (5D4 → 7F5 transition) is characterised by a lifetime slightly exceeding 2.6 ms. PL spectra of the Ag-containing glass show two broad weakly resolved emission bands in the violet-green spectral range attributed to Ag+ ions and nonplasmonic Ag nanoclusters. Decay kinetics of these bands are nonmonoexponential, characterised by an average lifetime in the microsecond range. A significant enhancement of the PL intensity and PL QY of Tb3+ ions was observed in Tb-Ag codoped LTB glass in comparison with Tb-doped LTB glass. The excitation energy transfer (EET) mechanisms from Ag+ ions and Ag nanoclusters to Tb3+ ions were explored.

Measurement of the multi-frequency resonator of a Coriolis vibration gyroscope using the standing wave rotation method

The possibility of determining the frequency split of a resonator in a Coriolis vibratory gyroscope by altering the position of the standing wave is considered. This method is proposed for diagnosing frequency split at various stages of gyroscope production and operation. The effect of stepwise changes in the standing wave angle and it continuous standing wave rotation on the resonator's excitation frequency are demonstrated. The examples of frequency split calculation based on measurements are presented. The advantages of the proposed frequency split measurement method are highlighted.

Revealing Single-Molecule Photocurrent Generation Mechanisms under On- and Off-Resonance Excitation.

We investigate photocurrent generation mechanisms in a pentacene single-molecule junction using subnanometer resolved photocurrent imaging under both on- and off-resonance laser excitation. By employing a wavelength-tunable laser combined with a lock-in technique, net photocurrent signals are extracted to elucidate photoinduced electron tunneling processes. Under off-resonance excitation, photocurrents are found to arise from photon-assisted tunneling, with contributions from three distinct frontier molecular orbitals at different bias voltages. In contrast, under resonance excitation, photocurrents are found to be significantly enhanced at negative bias voltages, exhibiting a spatial distribution linked to molecular electronic transitions and associated transition dipoles. This study reveals the contributions of different frontier molecular orbitals in the photon-assisted tunneling processes under off-resonance excitation, while molecular optical transitions are also found to be important at negative bias under resonance excitation. These findings could be instructive to the design and optimization of advanced optoelectronic devices.

Mirror resonances in Be9 and B9 within an α+α+N model

Using an α+α+N three-body model, we describe the ground and excited unbound states above the three-body threshold of A=9 mirror nuclei. We investigate the energy levels of low-lying and highly excited resonances below ≈10MeV excitation energy of Be9 and B9 mirror nuclei with the complex-scaling method. The same number of solutions are found for both mirror nuclei, namely, thirteen resonances, 3/21−4−, 5/21−3−, 1/21−3−, 7/21,2−, and 9/2−, including the ground state for odd parity states, and eight resonances 5/21,2+, 3/21,2+, 7/21,2+, and 9/21,2+, for even-parity states with the exception of the low-lying 1/2+ state. These results are compared with experimentally observed and other theoretically calculated results. The band structures of odd and even parity states for both Be9 and B9 mirror nuclei are discussed in relation to the effect of the Coulomb energy difference. Published by the American Physical Society 2024

Gallium nitride ultra-wideband terahertz absorber based on periodic pyramidal array

Abstract Gallium nitride (GaN) has garnered significant attention due to its unique properties. Here, we present, for the first time, a polarization-independent ultra-wideband absorber in the terahertz band, consisting of a pyramidal GaN array and a GaN substrate. Numerical simulation results indicate that the designed absorber exhibits excellent absorption performance in the range of 0.39 to 1.98 THz, with a center frequency of 1.185 THz. The relative bandwidth ratio is 134.2%, and the absorption exceeds 90%. The equivalent circuit model (ECM) further illustrates the ultra-wideband strong absorption characteristics of the proposed absorber. The simulated electromagnetic field distribution indicates that the perfect absorption of the designed absorber is attributed to the excitation of electromagnetic resonance. Additionally, due to the high structural symmetry, the absorber exhibits polarization-independent properties and maintains high absorption performance at large incidence angles. In the future, this holds great promise for optical applications, including detector devices, photo detection equipment, and solar energy collection systems.

Stability and dynamic behavior of in-plane transporting plates under internal resonance and two-frequency parametric excitation

Stability and dynamic behavior of in-plane transporting plates under internal resonance and two-frequency parametric excitation

Electronic Spectroscopy of the Halogenated Criegee Intermediate, ClCHOO: Experiment and Theory.

A chlorine-substituted Criegee intermediate, ClCHOO, is photolytically generated using a diiodo precursor, detected by VUV photoionization at 118 nm, and spectroscopically characterized via ultraviolet-visible (UV-vis)-induced depletion of m/z = 80 under jet cooled conditions. UV-vis excitation resonant with a π* ← π transition yields a significant ground state depletion, indicating a strong electronic transition and rapid photodissociation. The broad absorption spectrum peaks at 350 nm and is attributed to contributions from both syn (∼70%) and anti (∼30%) conformers of ClCHOO based on spectral simulations using a nuclear ensemble method. Electronic structure theory shows significant differences in the vertical excitation energies of the two conformers (330 and 371 nm, respectively) as well as their relative stabilities in the ground and excited electronic states associated with the π* ← π transition. Natural bond orbital analysis reveals significant and nonintuitive nonbonding contributions to the relative stabilities of the syn and anti conformers.