Excitation Intensity Research Articles

Steady-state dynamic response analysis of single-degree-of-freedom dual frame-wall resilient system

A mixed dual frame-wall resilient system, composed of a high-strength moment-resisting steel frame (HS-MRF) and self-centering steel plate shear walls (SC-SPSWs), was proposed to address the issue of frame expansion. To study the steady-state dynamic responses of the structural system, an analytical solution of a single-degree-of-freedom nonlinear oscillator under harmonic excitation was solved using the method of averaging. The steady-state responses of HS-MRF, self-centering frame and steel plate shear wall that are represented by the bilinear, self-centering and pinching hysteresis, respectively, were studied individually, followed by a full system study. A stability analysis was also carried out to evaluate the behaviour of the singular points. The results show that the hysteretic damping in the bilinear system can significantly reduce the resonance, and the responses are always stable. Jump phenomenon occurs in the self-centering system, and increasing the post-yield stiffness can reduce the nonlinearity, thus decreasing the resonance and unstable region. Unbounded resonance responses appear in the pinching system under large excitation but can change to jump behaviour under small excitation. A left-unbounded unstable region was also found when the unloading force is small. In the combined-hysteresis system, increasing the portion of bilinear hysteresis has negligible effects on the resonance but can reduce the nonlinearity under lower excitation intensities. However, under higher intensities, increasing bilinear hysteresis can significantly decrease peak responses and reduce both the jump and unbounded phenomena. The unstable regions also strongly depend on the ratio of hysteretic models. These findings shed light on the inherent dynamic properties of the dual frame-wall system and suggest that a well-design can achieve a favourable seismic performance.

Machine learning based model for plasma prediction in high power pulsed magnetron sputtering processes

The coating development using physical vapor deposition (PVD) is time intensive and expensive. The coating processes are usually developed and improved based on the operator's experience. In order to improve the understanding of the processes during coating deposition, methods of plasma diagnostics can be used. However, this is time intensive and requires the installation of special diagnostics. The aim of the current study is to build a machine learning based model of PVD processes to predict the ionized to excited intensity ratio of the plasma species during the coating process. This enables a knowledge-based, cost-reduced process improvement. Based on measured data of different coating processes, the models were trained and tested in the current study. Therefore, a database was established by measuring process and plasma properties in hybrid processes of direct current magnetron sputtering and high power pulsed magnetron sputtering using an industrial coating unit. Different processes with variations of cathode powers and gas flows of the reactive gases oxygen and nitrogen were processed. The intensities of the ionized and excited species were measured using optical emission spectroscopy with six substrate side positioned collimators for spatial resolution to calculate the intensity ratios. The data was measured time resolved during the coating process. Compared to the measured data, the predictions show similar trends and values for the species within the coating chamber. The model was used to predict the influence of oxygen gas flow for CrAlON coating development. Furthermore, the models can be used for a more targeted process development. This can contribute to the application oriented adjustment of the coating processes and the coating properties.

Photon Upconversion in a Vapor Deposited 2D Inorganic-Organic Semiconductor Heterostructure.

Energy transfer processes may be engineered in van der Waals heterostructures by taking advantage of the atomically abrupt, Å-scale, and topologically tailorable interfaces within them. Here, we prepare heterostructures comprised of 2D WSe2 monolayers interfaced with dibenzotetraphenylperiflanthene (DBP)-doped rubrene, an organic semiconductor capable of triplet fusion. We fabricate these heterostructures entirely through vapor deposition methods. Time-resolved and steady-state photoluminescence measurements reveal rapid subnanosecond quenching of WSe2 emission by rubrene and fluorescence from guest DBP molecules at 612 nm (λexc = 730 nm), thus providing clear evidence of photon upconversion. The dependence of the upconversion emission on excitation intensity is consistent with a triplet fusion mechanism, and maximum efficiency (linear regime) of this process occurs at threshold intensities as low as 110 mW/cm2, which is comparable to the integrated solar irradiance. This study highlights the potential for advanced optoelectronic applications employing vdWHs which leverage strongly bound excitons in monolayer TMDs and organic semiconductors.

Nonlinear dynamics analysis of enhancing energy harvesting from intense vibration based on improved asymmetric bistable stochastic resonance model

While the improved bistable energy harvesting (IBEH) system is excellent at harvesting energy from weak excitation signals, it is still inadequate at harvesting energy from intense excitation signals. Due to the strict resonance problem, energy harvesting strategies for intense excitation modes are not yet mature. Stochastic resonance seems to be a suitable solution for intense excitation vibration energy harvesting. An asymmetric improved bistable energy harvesting (AIBEH) system is proposed to address this issue by varying the position of the fixed-end magnet. Combining the AIBEH system with stochastic resonance theory and simulation results demonstrate that by simultaneously moving the fixed-end magnet up or down, the depth of a single potential well can be reduced while maintaining two stable state points, decreasing the slope of the potential wall on one side and increasing the dynamic output of the system under intense excitation signals. The research develops a mathematical model of the AIBEH system and numerically solves the electromechanical coupling control equations. The potential energy of three systems is analyzed: IBEH, AIBEH, and ABEH (asymmetric bistable energy harvesting). The Kramers rate and signal-to-noise ratio are derived for an asymmetric bistable system under a harmonic excitation signal and Gaussian white noise. In addition, the effects of harmonic excitation and additional noise on the AIBEH capture performance are investigated. The simulation results indicate that the harvesting performance of AIBEH is superior to that of IBEH at intense excitation.

The improvement of stochastic averaging method to solve the ship rolling response excited by narrow-band waves

The stochastic averaging method of energy envelope can accurately solve the random motion response under the excitation of white noise. The noise had to fulfill the condition of strong mixing which roughly means that the process has to be broad-band. However, the sea conditions in practical engineering conditions are narrow-band spectra. Research on applicability of the stochastic averaging method of energy envelope shows that for narrow-band excitation, the damping of the system and excitation intensity should be small, and the excitation bandwidth should be large. Based on the above background, the improvement of stochastic averaging method of energy envelope under narrow-band waves is studied. The phase angle θ is introduced to characterize the relationship between kinetic energy and potential energy of the system. The drift coefficients and diffusion coefficients are averaged with respect to the period of θ. When the excitation frequency is in the lock-in field, large parametric rolling appears. The stationary probability density function (PDF) of the roll angle obtained by solving the Fokker-Planck-Kolmogorov (FPK) equation compares well with Monte Carlo simulation in the lock-in field. The improved method can relax the limitation of broad-band excitation required by stochastic averaging method. It can also consider both the nonlinear damping and nonlinear restoring force of roll motion. Therefore, the improved method is an efficient way to calculate the nonlinear roll response of ships in real sea conditions.

Effect of meridian sinew releasing technique on moxibustion sensation of heat-sensitive moxibustion in patients with knee osteoarthritis

To observe the effect of meridian sinew releasing technique on moxibustion sensation of heat-sensitive moxibustion in patients with knee osteoarthritis (KOA).A total of 60 patients with KOA were randomly divided into an observation group and a control group, 30 cases each group. In the observation group, on the basis of the meridian sinew releasing technique, moxibustion sensation exploration method was applied at Dubi (ST 35) area on the affected side. In the control group, moxibustion sensation exploration method was applied at Dubi (ST 35) area on the affected side. The meridian sinew releasing technique was performed for 20 min each time, the moxibustion sensation exploration method was performed for 60 min each time, once a day for 3 days. The excitation rate, latency, duration time and intensity value of moxibustion sensation of heat-sensitive moxibustion were recorded on the 1st, 2nd and 3rd days of exploration in the two groups.The excitation rate on the 3rd day of exploration and total excitation rate in the observation group were higher than the control group (P<0.05). On the 1st, 2nd and 3rd days of exploration, the latency of moxibustion sensation of heat-sensitive moxibustion in the observation group was shorter than the control group (P<0.05), the duration time was longer than the control group (P<0.05), and the intensity value was higher than the control group (P<0.05).Meridian sinew releasing technique could improve the excitation rate of moxibustion sensation of heat-sensitive moxibustion in patients with KOA, shorten the latency, prolong the duration time, and improve the intensity value.目的：观察经筋手法松解术对膝关节骨关节炎（KOA）患者热敏灸感的影响。方法：将60例KOA患者随机分为观察组和对照组，每组30例。观察组在经筋手法松解术的基础上，于患侧犊鼻穴区行灸感探查法；对照组直接于患侧犊鼻穴区行灸感探查法。经筋手法松解术每次20 min，灸感探查法每次60 min，均每日1次，连续3 d。记录两组患者探查第1、2、3天热敏灸感激发率、潜伏期、持续时间、强度值。结果：观察组探查第3天热敏灸感激发率及总激发率高于对照组（P<0.05）。探查第1、2、3天，观察组热敏灸感潜伏期短于对照组（P<0.05），热敏灸感持续时间长于对照组（P<0.05），热敏灸感强度值高于对照组（P<0.05）。结论：经筋手法松解术可提高KOA患者热敏灸感激发率，缩短潜伏期，延长持续时间，提高强度值。.

Eu3+ doped Ca3LiZnV3O12 phosphors for four-mode optical thermometry

Optical thermometer has brought about the widespread attention on account of non-contact and high-sensitive advantages. In this work, a novel optical thermometry with four modes was designed in Ca3LiZnV3O12:Eu3+ (CLZVO:Eu3+) phosphors. Benefitting from energy transfer of VO43− to Eu3+, CLZVO:Eu3+ phosphors (irradiated by 342 nm light) generate emissions from VO43− and Eu3+ simultaneously. As temperature increases, luminescent intensities of VO43− and Eu3+ show different downward trends, resulting in luminescent color changing with temperature. Besides, the excitation spectra of VO43− show a red shift with temperature boosting. Based on above luminescent characteristics, FI (fluorescence intensity), FIR (fluorescence intensity ratio), CIE (Commission Internationale de L'Eclairage) coordinate, and EIR (excitation intensity ratio) modes of CLZVO:Eu3+ thermometry were obtained. The maximum SR (relative sensitivity) values of each modes attain 2.56 %K−1 (340 K, FI), 2.18 %K−1 (320 K, FIR), 0.492 %K−1 (400 K, CIE coordinate), and 1.60 %K−1 (303 K, EIR). The minimal SR of FI and FIR modes are higher than 1.38 %K−1 and 1.08 %K−1 in 303–513 K temperature range. Above outstanding properties manifest the potentiality of CLZVO:Eu3+ for monitoring temperature.

Component wave calculation and analysis of the acoustic field in a borehole within a three-phase porous medium

The knowledge of acoustic wave propagation in a borehole embedded in gas hydrate-bearing sediments is of great significance for the exploitation of gas hydrate. A gas hydrate-bearing sediment is a typical three-phase porous medium containing two solids and one fluid. However, until now, the borehole acoustic wavefield and its component waves within such a porous medium have never been calculated. In this work, a real-axis integration method is proposed to calculate the borehole acoustic field embedded in a three-phase porous medium based on the Biot-type three-phase theory. Meanwhile, a component wave approach, combined with the branch-cut integral method and the residue theorem, including residues at leaky poles is proposed to study the borehole wave propagation of a three-phase porous medium. The branch points and poles of the potential acoustic wave function are obtained, which correspond to the normal and leaky modes on various Riemann sheets. On this basis, the excitation intensity and waveforms of each component are obtained. The result shows that the waveform summed up from all individual waves agrees well with the full waveform calculated by real-axis integration, which provides a theoretical basis for the subsequent inversion of reservoir parameters by using the information of various mode waves.

Aerial Photoluminescence Imaging of Photovoltaic Modules

On‐site imaging of modules in photovoltaic (PV) systems requires contact‐free techniques with high throughput and low cost for commercial relevance. Photoluminescence imaging satisfies these requirements, but it has so far not been used for aerial imaging. Such a system faces unique engineering and operating challenges, including the need to mount a light source on the drone and identifying module defects from images taken under low‐ and nonuniform irradiance. Herein, in‐house developed photoluminescence aerial imaging (PLAI) setup is presented and it is demonstrated that it can be used to identify defects even with a difference of excitation intensity of up to 50%. The setup consists of a hexacopter aerial drone equipped with an illumination unit and a near‐infrared camera. The unit is capable of partially illuminating full‐sized modules at night and capturing the photoluminescence response. In the maiden flight, a throughput of 13.6 PV modules per minute is achieved, and a throughput of 300 PV modules per minute is feasible. It is shown that the setup can be used to detect and identify cracks and potential induced degradation with high levels of confidence. These findings are verified by cross correlation and comparing captured photoluminescence images to electroluminescence images taken indoors.

Distributed Bragg Reflector–Mediated Excitation of InAs/InP Quantum Dots Emitting in the Telecom C‐Band

Herein, it is demonstrated that optical excitation of InAs quantum dots (QDs) embedded directly in an InP matrix can be mediated via states in a quaternary compound constituting an InP/InGaAlAs bottom distributed Bragg reflector (DBR) and native defects in the InP matrix. It does not only change the carrier relaxation in the structure but could also lead to the imbalanced occupation of QDs with charge carriers, because the band structure favors the transfer of holes. Thermal activation of carrier transfer can be observed as an increase in the emission intensity versus temperature for excitation powers below saturation on the level of both an inhomogeneously broadened QD ensemble and single QD transitions. That increase in the QD emission is accompanied by a decrease in the emission from the InGaAlAs layer at low temperatures. Finally, carrier transfer between the InGaAlAs layer of the DBR and the InAs/InP QDs is directly proven by the photoluminescence excitation spectrum of the QD ensemble. The reported carrier transfer can increase the relaxation time of carriers into the QDs and thus be detrimental to the coherence properties of single and entangled photons. It is important to take it into account while designing QD‐based devices.

Photoinduced Triplet Depletion Allowing Higher-Resolution Afterglow

Afterglow emission allows for imaging that is independent of autofluorescence under ambient conditions. Although higher-resolution afterglow is required for increasing the quality of the autofluorescence-free emission imaging, increasing the excitation intensity to generate brighter afterglow emission decreases the resolution of afterglow images. Therefore, methods and materials that provide afterglow imaging with higher resolution remain to be developed. In this study, we performed photoinduced triplet depletion and demonstrated improved resolution of bright afterglow emission using the depletion. Triplet depletion is related to charge separation via photoionization from a triplet state caused by depletion and subsequent rapid singlet formation. Triplet excitons that accumulated in a solid material by excitation were depleted under irradiation using a depletion beam with a longer wavelength than the absorption wavelength of the material. A higher-resolution afterglow image with an improvement of 25% was obtained by simultaneously focusing a donut-shaped depletion beam and an excitation beam.

Dazzling green luminescent and biocompatible Tb3+ -activated lanthanum tungstate nanophosphors for group-III evaluation of latent fingerprints and anticancer applications

Dazzling green emission exhibiting Tb3+ ions doped lanthanum tungstate (LWO) nanophosphors were synthesized by a facile hydrothermally assisted solid-state reaction method. The nanophosphors were determined to have an orthorhombic structure using XRD analysis. In the optimized Tb3+: LWO nanophosphor, FE-SEM revealed aggregated non-uniform nanorods. TEM, FTIR, and XPS studies were performed to examine the material properties. A predominant excitation band was recorded at 488 nm (7F6→5D4) for the Tb3+ doped LWO nanophosphors, along with a moderately intense excitation band at 378 nm (7F6→5G6). Ravishing green emission at 544 nm (5D4→7F5) was obtained from Tb3+ ions containing LWO nanophosphors under excitation at 378 nm and 488 nm. We improved the green emission intensity by increasing the Tb3+ ion concentration up to 14 mol%, which was reduced after 14 mol% due to concentration quenching. The energy-level diagram shows the green radiative transition pathway. The CIE coordinates and color purity were computed for Tb3+: LWO nanophosphors from their emission profiles, and the evaluated coordinates were centralized in the strong green region. A high color purity of 90.1% was obtained appreciably from the optimized Tb3+: LWO nanophosphor. The lifetime of the green emission transition was systematically evaluated based on decay dynamics. The visualization of fingerprints was examined using the optimized green phosphor with an in-depth analysis of the Group-III level details. The non-cytotoxicity of Tb3+ (14 mol%): LWO nanophosphor was confirmed in normal WI-38 lung fibroblast cells. Moreover, these phosphors exhibited strong cytotoxicity against human breast cancer cells of MCF-7. From these results, the synthesized Tb3+ (14 mol%): LWO non-cytotoxic nanophosphor material is considered the best green luminescent material for latent fingerprints in forensic investigation, photonic and anticancer applications.

Anomalous power-dependent color tuning of Er upconverting luminescence via 1530 nm excitation

The upconversion color tuning of Lanthanide ions usually requires complex core–shell structures and excitation configurations. This work presents simple Er3+ doped Yttria phosphors capable of color change through the manipulation of 1530 nm excitation intensity. Compared to the reported results of Er3+ color change from green to red with the increase in excitation intensity, the formed color-tunable phosphors show an inverse change of red to green. The color tuning mechanisms are attributed to the competition between the upward absorption and the downward decay at the Er3+ intermediate state. Finally, the potential applications of the formed color-tunable phosphors are demonstrated. This work provides a simple solution for high-performance upconversion color tuning and thus shows wide application prospects.

Facilitation of controllable excitation in Rydberg atomic ensembles

Strongly-interacting Rydberg atomic ensembles have shown intense collective excitation effects due to the inclusion of single Rydberg excitation shared by multiple atoms in the ensemble. In this paper we investigate a counter-intuitive Rydberg excitation facilitation with a strongly-interacting atomic ensemble in the strong probe-field regime, which is enabled by the role of a control atom nearby. Differing from the case of a single ensemble, we show that, the control atom's excitation adds to a second two-photon transition onto the doubly-excited Rydberg state, arising an excitation facilitation for the ensemble atoms. Our numerical studies depending on the method of quantum Monte Carlo wave function, exhibit the observation constraints of this excitation facilitation effect under practical experimental conditions. The results obtained can provide a flexible control for the excitation of Rydberg atomic ensembles and participate further uses in developing mesoscopic Rydberg gates for multiqubit quantum computation.

Single SiGe quantum dot emission deterministically enhanced in a high-Q photonic crystal resonator.

We report the resonantly enhanced radiative emission from a single SiGe quantum dot (QD), which is deterministically embedded into a bichromatic photonic crystal resonator (PhCR) at the position of its largest modal electric field by a scalable method. By optimizing our molecular beam epitaxy (MBE) growth technique, we were able to reduce the amount of Ge within the whole resonator to obtain an absolute minimum of exactly one QD, accurately positioned by lithographic methods relative to the PhCR, and an otherwise flat, a few monolayer thin, Ge wetting layer (WL). With this method, record quality (Q) factors for QD-loaded PhCRs up to Q ∼ 105 are achieved. A comparison with control PhCRs on samples containing a WL but no QDs is presented, as well as a detailed analysis of the dependence of the resonator-coupled emission on temperature, excitation intensity, and emission decay after pulsed excitation. Our findings undoubtedly confirm a single QD in the center of the resonator as a potentially novel photon source in the telecom spectral range.

Complex exciton dynamics with elevated temperature in a GaAsSb/GaAs quantum well heterostructure

Exciton dynamics in a GaAsSb/GaAs quantum well (QW) heterostructure were investigated via both steady state and transient photoluminescence. The measurements at 10 K demonstrated the coexistence of localized excitons (LEs) and free excitons (FEs), while a blue-shift resulting from increased excitation intensity indicated their spatially indirect transition (IT) characteristics due to the type-II band alignment. With increasing temperature from 10 K, the LEs and FEs redistribute, with the LEs becoming less intense at relatively higher temperature. With increasing temperature to above 80 K, electrons in GaAs are able to overcome the small band offset to enter inside GaAsSb and recombine with holes; thus, a spatially direct transition (DT) appeared. Hence, we are able to reveal complex carrier recombination dynamics for the GaAsSb/GaAs QW heterostructure, in which the “S” shape behavior is generated not only by the carrier localization but also by the transformation from IT to DT with elevated temperature.

Ultrafast Control of the Optical Transition in Type-II Colloidal Quantum Wells

Manipulating the optical transition in semiconductors at ultrashort timescales is of both fundamental interest and central importance for emerging photonic applications. Traditionally, this manipulation is realized by electrostatic gating via Stark effects or band-gap renormalizations. Here, we report an ultrafast and all-optical route to engineer an indirect transition in core–crown colloidal quantum wells (CQWs), namely, CdSe/CdTe, with a type-II band alignment. Following the intense laser pulse excitation, the indirect band transition energy exhibits a pronounced blueshift–redshift crossover on the picosecond timescale, stemming from the formation and dissipation of the transient electric field (E-field) that forms upon photoexcitation to compensate for the driving force provided by the band offsets. Both the energy shift and dynamics of the transient E-field can be modulated optically by tuning the laser pulse excitation fluence. Our finding demonstrates a strong analogy between the type-II heterojunction and a p–n junction with respect to carrier equilibrium processes, which holds promise to facilitate the integration of CQWs within optical switching networks.

Electronic excitation induced non-thermal phase transition of tungsten

The electronically excited states of tungsten (W) material tuned by ultrafast laser irradiation cause intriguing jumps between different Born-Oppenheimer surfaces. This may give rise to a structural phase transformation of BCC-to-FCC or BCC-to-HCP on a very short time scale, which is still debated. By performing calculations on W with both density functional theory and a tight-binding approach, a martensitic phase transformation from BCC phase to HCP phase in bulk W is predicted at a threshold (15,500 ± 500 K) of electronic temperatures, where the HCP phase is found to be more stable than both BCC and FCC phases under intense electronic excitations. Additionally, it is proposed that the non-thermal phase transition could potentially be probed through experimental measurements of the c/a ratio of system in the future. The mechanism underlying the BCC-to-HCP transformation in the electronically excited bulk W system is analyzed under the level of electronic structure. It is found that the irradiation-induced changes of the density of states at the Fermi level could drive the structural phase transformation. This provides new insight into the atomic-level non-thermal phase transition process of W under intense electronic excitations.

Coulomb enhancement of high harmonic generation in monolayer transition metal dichalcogenides.

High harmonic generation (HHG) in monolayer MoS2 is studied using fully microscopic many-body models based on the semiconductor Bloch equations and density functional theory. It is shown that Coulomb correlations lead to a dramatic enhancement of HHG. In particular, near the bandgap, enhancements of two orders of magnitude or more are observed for a wide range of excitation wavelengths and intensities. For excitation at excitonic resonances, strong absorption leads to spectrally broad sub-floors of the harmonics that is absent without Coulomb interaction. The widths of these sub-floors depend strongly on the dephasing time for polarizations. For times of the order of 10 fs the broadenings are comparable to the Rabi energies and reach one electronvolt at fields of approximately 50 MV/cm. The intensities of these contributions are approximately four to six orders below the peaks of the harmonics.

Observation of Charge Separation Enhancement in Plasmonic Photocatalysts under Coupling Conditions.

Surface plasmon resonance-induced charge separation plays key roles in plasmon-related applications, especially in photocatalysis and photovoltaics. Plasmon coupling nanostructures exhibit extraordinary behaviors in hybrid states, phonon scattering, and ultrafast plasmon dephasing, but plasmon-induced charge separation in these materials remains unknown. Here, we design Schottky-free Au nanoparticle (NP)/NiO/Au nanoparticles-on-a-mirror plasmonic photocatalysts to support plasmon-induced interfacial hole transfer, evidenced by surface photovoltage microscopy at the single-particle level. In particular, we observe a nonlinear increase in charge density and photocatalytic performance with an increase in excitation intensity in plasmonic photocatalysts containing hot spots as a result of varying the geometry. Such charge separation increased the internal quantum efficiency by 14 times at 600 nm in catalytic reactions as compared to that of the Au NP/NiO without a coupling effect. These observations provide an improved understanding of charge transfer management and utilization by geometric engineering and interface electronic structure for plasmonic photocatalysis.