Continuous Excitation Research Articles

Radical Afterglow Emission Harnessed by Doping N,N’‐Diaryl‐5,10‐Dihydrophenazines to Epoxy Resins

AbstractDeveloping radical‐induced afterglow emission under ambient conditions is challenging since newly formed radical species are susceptible to air and water. In this work, long afterglow materials (up to 4 s) are realized by doping a series of N,N’‐diaryl‐5,10‐dihydrophenazine (DPP)derivatives into rigid cycloaliphatic epoxy resins (CER). The afterglow is found to result from the interaction between the matrix and the excited states of the dopants through the generation of radical species under continuous UV excitation, which can be regulated by the peripheral functional groups of the N‐phenyl substituents. Density functional theory (DFT) calculations predict that the introduction of electron‐withdrawing groups hinders the afterglow emission, which may be related to the reducing reduction potential and inefficient spin‐orbit coupling (SOC) coefficients. The afterglow emission of the radical‐based systems demonstrates a bright opportunity for information encryption, anti‐counterfeiting, and photolithography.

Bimodal role of Cr3+ ions: the nanoscaled photothermal agent and luminescence thermometry

The development of a photothermal agent and a luminescent thermometer within a single nanoparticle is a challenging task since optical heating is efficient for high concentrations of dopants that limit the intensity of luminescence via concentration quenching. Therefore, in this work, it is proven that the use of a relatively small amount of Cr3+ ions as a dopant in NaGdF4:Yb3+,Nd3+ nanoparticles enables the creation of a photothermal agent with an external light-to-heat conversion efficiency among the highest for luminescent materials described so far. At the same time, the Cr3+→Nd3+→Yb3+ energy transfer enables the development of a lifetime-based luminescent thermometer with sensitivity exceeding SR = 1.78%/K in the physiological temperature range. In addition, the pulsed or continuous excitation mode enables separate activation of thermometry and heating functionalities.

Basal forebrain parvalbumin neurons modulate vigilant attention and rescue deficits produced by sleep deprivation.

Attention is impaired in many neuropsychiatric disorders, as well as by sleep disruption, leading to decreased workplace productivity and increased risk of accidents. Thus, understanding the neural substrates is important. Here we test the hypothesis that basal forebrain neurons that contain the calcium-binding protein parvalbumin modulate vigilant attention in mice. Furthermore, we test whether increasing the activity of basal forebrain parvalbumin neurons can rescue the deleterious effects of sleep deprivation on vigilance. A lever release version of the rodent psychomotor vigilance test was used to assess vigilant attention. Brief and continuous low-power optogenetic excitation (1 s, 473 nm @ 5 mW) or inhibition (1 s, 530 nm @ 10 mW) of basal forebrain parvalbumin neurons was used to test the effect on attention, as measured by reaction time, under control conditions and following 8 hr of sleep deprivation by gentle handling. Optogenetic excitation of basal forebrain parvalbumin neurons that preceded the cue light signal by 0.5 s improved vigilant attention as indicated by quicker reaction times. By contrast, both sleep deprivation and optogenetic inhibition slowed reaction times. Importantly, basal forebrain parvalbumin excitation rescued the reaction time deficits in sleep-deprived mice. Control experiments using a progressive ratio operant task confirmed that optogenetic manipulation of basal forebrain parvalbumin neurons did not alter motivation. These findings reveal for the first time a role for basal forebrain parvalbumin neurons in attention, and show that increasing their activity can compensate for disruptive effects of sleep deprivation.

Combined Polarization/Magnetic Modulation of a Transverse NMR Gyroscope

In this paper, we describe a new approach to the continuous operation of a transverse spin-exchange optically pumped NMR gyroscope that utilizes modulation of both the applied bias field and the optical pumping. We demonstrate the simultaneous, continuous excitation of 131Xe and 129Xe using this hybrid modulation approach and the real-time demodulation of the Xe precession using a custom least-squares fitting algorithm. We present rotation rate measurements with this device, with a common field suppression factor of ∼1400, an angle random walk of 21 μHz/Hz, and a bias instability of ∼480 nHz after ∼1000 s.

Whispering gallery mode micro-lasing in CsPbI3 quantum dots coated on TiO2 microspherical resonating cavities.

Whispering gallery mode (WGM) lasing in CsPbI3 quantum dots (QDs) coated on TiO2 spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI3-QDs gain medium strongly couples with a TiO2 microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct threshold point of 708.7 W/cm2. Lasing intensity increases three to four times as the power density increases by one order of magnitude beyond the threshold point when the microcavities are excited with a 632-nm laser. WGM microlasing with quality factors as high as Q∼1195 is demonstrated at room temperature. Quality factors are found to be higher for smaller TiO2 microcavities (∼2 µm). CsPbI3-QDs/TiO2 microcavities are also found to be photostable even after continuous laser excitation for 75 minutes. The CsPbI3-QDs/TiO2 microspheres are promising as WGM-based tunable microlasers.

Voltage Modulation of Nanoplasmonic Metal Luminescence from Nano-Optoelectrodes in Electrolytes.

Metallic nanostructures supporting surface plasmon modes can concentrate optical fields and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nanothermometry and chemical reaction monitoring applications. Although there is growing interest in nanoplasmonic metal luminescence, its dependence on voltage modulation has received limited attention in research investigations. Also, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique typically ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. Here, we report a combined experiment and theory study on dynamic voltage-modulated nanoplasmonic metal luminescence from hotspots at the electrode-electrolyte interface using multiresonant nanolaminate nano-optoelectrode arrays. Our EC-SERS measurements under 785 nm continuous wavelength laser excitation demonstrate that short-wavenumber nanoplasmonic metal luminescence associated with plasmon-enhanced electronic Raman scattering (PE-ERS) exhibits a negative voltage modulation slope (up to ≈30% V-1) in physiological ionic solutions. Furthermore, we have developed a phenomenological model to intuitively capture the plasmonic, electronic, and ionic characteristics at the metal-electrolyte interface to understand the observed dependence of the PE-ERS voltage modulation slope on voltage polarization and ionic strength. The current work represents a critical step toward the general application of nanoplasmonic metal luminescence signals in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial electrochemical monitoring.

Dynamic performance and temperature rising characteristic of a high-speed on/off valve based on pre-excitation control algorithm

High speed on/off valve (HSV) is an essential component in aerospace digital hydraulic systems (ADHS). Dynamic performance and temperature rising characteristic are two important features, which determine the performance of HSV, and affect the response speed and reliability of ADHS. Increasing the driving voltage is an effective method for improving the dynamic performance of HSV. However, continuous high voltage excitation will lead to more wasted energy, higher temperature rising and lower reliability. To solve this problem, a pre-excitation control algorithm (PECA) is proposed in this paper based on the theoretical model of the influence of electrical parameters on dynamic performance and temperature rising characteristics. In PECA, an appropriate initial coil current is generated by pre-excitation instead of increasing driving voltage, which significantly shortens the switching delay time. Then, based on real-time current online calculation and feedback mechanism, the adaptive switching of five equivalent voltages is realized. Consequently, the coil current can be rapidly kept at the expected state without consuming more energy and generating more heat. Results indicate that compared with conventional PWM control algorithm, the PECA can improve dynamic performance of HSV, shorten the total switching time by 71.5%, and increase the maximum operation frequency. Therefore, the linear area of flow characteristic is expended by 80.0%, the adjusting time of HSV-controlled system is reduced by 23%, while shortening steady error by 46.7%. Moreover, the temperature rising characteristics of HSV are better, the maximum operation temperature is reduced by 68.6%, and the time to reach the steady state temperature is shortened by 20%. From the results, it can be concluded that the PECA is not only an effective and practical control algorithm for improving the performance of HSVs and HSV-controlled systems while reducing the heat generation and decreasing the temperature rising of HSV, but also can be a potential solution in ADHS.

An Efficient Broadband Symmetrical Doherty Power Amplifier With Extended Back-Off Range

In this brief, a symmetrical Doherty power amplifier (DPA) which exhibits enhanced efficiency, bandwidth and output power back-off range by phase compensation, is proposed. This proposed architecture compensates the phase deviation between main and auxiliary amplifiers mainly caused by the load modulation circuit and parasitic parameters of transistors. With phase compensation, both saturation efficiency and bandwidth are significantly improved while maintaining an extended output back-off range. For verification, a 2.05–2.8-GHz symmetrical DPA is designed, fabricated and measured. Under continuous wave excitation, measurement results show that the implemented DPA exhibits drain efficiency of 40%–49% at 9 dB output back-off level and 66%–76% at saturation with a maximum output power of 43.9–44.9-dBm over the entire band.

Observation of coherently coupled cation spin dynamics in an insulating ferrimagnetic oxide

Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni0.65Zn0.35Al0.8Fe1.2O4) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe2+/3+ and Ni2+ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within ≈2°. Moreover, the effective spin relaxation is identical to within <10% for all magnetic cations in the ferrite. Thus, we validate the oft-assumed “ferromagnetic-like” dynamics in the resonantly driven ferrimagnetic oxide: the magnetic moments from different cations precess as a coherent, collective magnetization, despite the high contents of nonmagnetic Zn2+ and Al3+ diluting the exchange interactions.

Confocal LiDAR for remote high-resolution imaging of auto-fluorescence in aquatic media

Spatially resolved in situ monitoring of plankton can provide insights on the impacts of climate change on aquatic ecosystems due to their vital role in the biological carbon pump. However, high-resolution underwater imaging is technically complex and restricted to small close-range volumes with current techniques. Here, we report a novel inelastic scanning confocal light detection and ranging (LiDAR) system for remote underwater volumetric imaging of fluorescent objects. A continuous wave excitation beam is combined with a pinhole in a conjugated detection plane to reject out-of-focus scattering and accomplish near-diffraction limited probe volumes. The combination of bi-directional scanning with remote focusing enables the acquisition of three-dimensional data. We experimentally determine the point spread and axial weighting functions, and demonstrate selective volumetric imaging of obstructed layers through spatial filtering. Finally, we spatially resolve in vivo autofluorescence from sub-millimeter Acocyclops royi copepods to demonstrate the applicability of our novel instrument in non-intrusive morphological and spectroscopic studies of aquatic fauna. The proposed system constitutes a unique tool e.g. for profiling chlorophyll distributions and for quantitative studies of zooplankton with reduced interference from intervening scatterers in the water column that degrade the the performance of conventional imaging systems currently in place.

Energy transfer mechanisms in binary tree-structured oscillator with nonlinear energy sinks

We study a binary tree-structured multi-degree-of-freedom nonlinear oscillator with impulsive and continuous excitations. The response of this model is studied for excitations that are applied to the largest masses. It is shown how choosing the mass of the smallest blocks influences the response of the system regarding the dissipation and how efficient targeted energy transfer is realized in the system. The simplified frequency energy plot is introduced as a means of analyzing the response of multi-degree-of-freedom systems for impulsive excitations. For continuous excitations, it is shown that the smallest masses (nonlinear energy sinks) are active only inside specific nonlinear frequency bands when the excitation amplitude is sufficiently high.

All-Optical Switching Based on Sub-Bandgap Photoactivation of Charge Trapping in Metal Halide Perovskites.

Controllable optical properties are crucial for the application of light-emitting materials in optical devices. In this work, controllable photoluminescence in metal halide perovskite crystals is realized via photoactivation of their defects. It is found that under continuous excitation, the photoluminescence intensity of a CH3 NH3 PbBr3 crystal can be fully controlled by sub-bandgap energy photon illumination. Such optically controllable emission behavior is rather general as it is observed also in CsPbBr3 and other perovskite materials. The switching mechanism is assigned to reversible light-induced activation/deactivation of nonradiative recombination centers, the presence of which relates to an excess of Pb during perovskite synthesis. Given the success of perovskites in photovoltaics and optoelectronics, it is believed that the discovery of green luminescence controlled by red illumination will extend the application scope of perovskites toward optical devices and intelligent control.

Interface versus Bulk Light-Induced Switching in Spin-Crossover Molecular Ultrathin Films Adsorbed on a Metallic Surface.

Spin-crossover molecules present the unique property of having two spin states that can be controlled by light excitation at low temperature. Here, we report on the photoexcitation of [FeII((3, 5-(CH3)2Pz)3BH)2] (Pz = pyrazolyl) ultrathin films, with thicknesses ranging from 0.9 to 5.3 monolayers, adsorbed on Cu(111) substrate. Using X-ray absorption spectroscopy measurements, we confirm the anomalous light-induced spin-state switching observed for sub-monolayer coverage and demonstrate that it is confined to the first molecular layer in contact with the metallic substrate. For higher coverages, the well-known light-induced excited spin-state trapping effect is recovered. Combining continuous light excitation with thermal cycling, we demonstrate that at low temperature light-induced thermal hysteresis is measured for the thicker films, while for sub-monolayer coverage, the light enables extension of the thermal conversion over a large temperature range. Mechanoelastic simulations underline that, due to the intermolecular interactions, opposite behaviors are observed in the different layers composing the films.

Track Decay Rate (TDR) Measurement Method for Reactive Damping by Tuned Mass Damper (TMD)

TDR measures the rate of vibration decay along rail in dB/m. Higher TDR leads to lower noise radiation. However, new railways are often having low TDR due to the use of resilient fasteners (to provide vibration isolation between rail and supporting structure for ground borne noise concerns), which leads to high noise radiation. Rail damper is used to increase TDR (thus reduces railway noise), where TMD is an efficient damping mechanism dissipating the vibration energy of the rail. TMD provides reactive damping force, maximised after a few cycles of oscillations. TMD force is stronger with continuous excitation than impulse excitation. For convenient purposes in the industry, TDR measurements are primarily conducted by impulse method, which do not allow sufficient time to include reactive TMD force. Therefore, impulse excitation TDR is smaller than continuous excitation TDR. Continuous excitation TDR is considered to reflect more of the real case of wheel/rail interaction excitation during train running. Besides, TDR in terms of time decay in dB/s is an alternative approach for evaluating noise performance of the rail. This paper presents TDR measurement results under different conditions, e.g., impulse excitation against continuous excitation; freely supported short rail (~6m), short rail (~6m) with resilient fastener support as well as site measurements in continuous welded rails.

Optimization of the Thin Waveguide for Double-Parabolic-Reflectors Ultrasonic Transducers (DPLUS) for Thermal Ablation.

Interstitial and intracavitary ultra- sound applicators had been developed and studied for minimally invasive treatments (MIT). However, the acoustic outputs are limited by the small-size PZT. We therefore studied the acoustic waveguide (AW) applicator which enables the use of a large-size PZT, and we aimed to advance AW applicators towards thermal ablation applications. Double parabolic reflectors wave-guided ultrasonic transducer (DPLUS) was introduced which has two parabolic reflectors for enhancing the acoustic output. Theoretical modeling was conducted for optimizing the DPLUS thin waveguide. Modeling results showed that optimal a/Λ (thin waveguide radius/wavelength) can be found and the optimal a depends on the excitable vibration amplitude in the thin waveguide. A local optimal a/Λ= 0.2392 was considered the best choice, which results in the optimal frequency of 2.2 MHz at the radius a of 0.6 mm. To verify this optimal frequency, experiments under two working frequencies of 1.0282 MHz and 2.2579 MHz were conducted. Temperature rise curves in the chicken breast tissue showed good agreements between experiments and modeling results, which proved the effectiveness of the modeling. In addition, experiments showed an ablated area with a diameter of 1.03±0.12 mm under continuous excitation of 2.2579 MHz and 5 s. The developed DPLUS advanced the AW applicators towards thermal ablation applications. This study provides the evidence for recognizing AW applicators as a technique for thermal ablation.

Numerical simulation and observed rotational relaxation in CW and pulsed HBr-filled hollow-core fiber lasers.

Gas-filled hollow-core fiber (HCF) lasers have emerged as a promising technology for generating mid-infrared lasers. A four-energy level system laser model is presented to predict the performance of optically pumped HBr-filled HCF lasers under continuous wave (CW) and pulsed excitations. The steady state condition is considered in CW pumping and the characteristics of simulated population density and power distribution along HCF are investigated. The finite-difference time-domain method is employed in pulsed pumping and the simulated evolutions of pump pulse and laser pulse at different positions along the HCF are studied. In addition, the phenomena of rotational relaxation in HBr-filled HCF lasers are investigated experimentally for the first time, to the best of our knowledge, showing that using the absorption lines away from the strongest absorption lines and tuning the pump wavelength deviating from the center of the absorption line makes the rotational relaxation occur easily. The demonstration is conductive to reveal the underlying mechanism of such gas-filled HCF lasers.

Combined Fluorescence Fluctuation and Spectrofluorometric Measurements Reveal a Red-Shifted, Near-IR Emissive Photo-Isomerized Form of Cyanine 5.

Cyanine fluorophores are extensively used in fluorescence spectroscopy and imaging. Upon continuous excitation, especially at excitation conditions used in single-molecule and super-resolution experiments, photo-isomerized states of cyanines easily reach population probabilities of around 50%. Still, effects of photo-isomerization are largely ignored in such experiments. Here, we studied the photo-isomerization of the pentamethine cyanine 5 (Cy5) by two similar, yet complementary means to follow fluorophore blinking dynamics: fluorescence correlation spectroscopy (FCS) and transient-state (TRAST) excitation-modulation spectroscopy. Additionally, we combined TRAST and spectrofluorimetry (spectral-TRAST), whereby the emission spectra of Cy5 were recorded upon different rectangular pulse-train excitations. We also developed a framework for analyzing transitions between multiple emissive states in FCS and TRAST experiments, how the brightness of the different states is weighted, and what initial conditions that apply. Our FCS, TRAST, and spectral-TRAST experiments showed significant differences in dark-state relaxation amplitudes for different spectral detection ranges, which we attribute to an additional red-shifted, emissive photo-isomerized state of Cy5, not previously considered in FCS and single-molecule experiments. The photo-isomerization kinetics of this state indicate that it is formed under moderate excitation conditions, and its population and emission may thus deserve also more general consideration in fluorescence imaging and spectroscopy experiments.

Quantum Cutting in KGd(CO3)2:Tb3+ Green Phosphor

Phosphors with a longer excitation wavelength exhibit higher energy conversion efficiency. Herein, quantum cutting KGd(CO3)2:Tb3+ phosphors excited by middle-wave ultraviolet were synthesized via a hydrothermal method. All the KGd(CO3)2:xTb3+ phosphors remain in monoclinic structures in a large Tb3+ doping range. In the KGd(CO3)2 host, 6D3/2 and 6I17/2 of Gd3+ were employed for quantum cutting in sensitizing levels. The excited state electrons could easily transfer from Gd3+ to Tb3+ with high efficiency. There are three efficient excited bands for quantum cutting. The excited wavelengths of 244, 273, and 283 nm correspond to the transition processes of 8S7/2→6D3/2 (Gd3+), 8S7/2→6I17/2 (Gd3+), and 7F6→5F4 (Tb3+), and the maximum quantum yields of KGd(CO3)2:Tb3+ can reach 163.5, 119, and 143%, respectively. The continuous and efficient excitation band of 273-283 nm can well match the commercial 275 nm LED chip to expand the usage of solid-state light sources. Meanwhile, the phosphor also shows good excitation efficiency at 365 nm in a high Tb3+ doping concentration. Therefore, KGd(CO3)2:Tb3+ is an efficient green-emitting phosphor for ultraviolet-excited solid-state light sources.

Multi-color UCNPs/CsPb(Br1-xIx)3 for upconversion luminescence and dual-modal anticounterfeiting.

Advanced hybrid materials have attracted extensive attention in optoelectronics and photonics application due to their unique and excellent properties. Here, the multicolor upconversion luminescence properties of the hybrid materials composed of CsPbX3(X = Br/I) perovskite quantum dots and upconversion nanoparticles (UCNPs, core-shell NaYF4:25%Yb3+,0.5%Tm3+@NaYF4) is reported, achieving the upconversion luminescence with stable and bright of CsPbX3 perovskite quantum dots under 980 nm excitation. Compared with the nonlinear upconversion of multi-photon absorption in perovskite, UCNPs/CsPbX3 achieves lower power density excitationby using theUCNPs as the physical energy transfer level, meeting the demand for multi-color upconversion luminescence in optical applications. Also, the UCNPs/CsPbX3 combined with ultraviolet curable resin (UVCR) shows excellent water and air stability, which can be employed as multicolor fluorescent ink for screen printing security labels. Through the conversion strategy, the message of the security labels can be encrypted and decrypted by using UV light and a 980 nm continuous wave excitation laser as a switch, which greatly improves the difficulty of forgery. These findings provide a general method to stimulate photon upconversion and improve the stability of perovskite nanocrystals, which will be better applied in the field of anti-counterfeiting.

Synthesis of an Ultra-Wideband Pulse by a Log-Periodic Antenna with Continuous Excitation by Harmonic Oscillations

Synthesis of an Ultra-Wideband Pulse by a Log-Periodic Antenna with Continuous Excitation by Harmonic Oscillations