Off-resonance Conditions Research Articles

Microwave field vector detector based on the off-resonant spin rectification effect

Normal microwave (MW) electromagnetic field detectors convert microwave power into voltages, which results in loss of the vector characteristics of the microwave field. In this work, we developed a MW magnetic field (h-field) vector detector based on the off-resonant spin rectification effect. By measuring and analyzing the angle dependence of the rectification voltages under off-resonant conditions, we can extract the three components of the h-field. As an initial test of this method, we obtained the h-field distributions at 5.4 GHz generated by a coplanar waveguide with sub-wavelength resolution. Compared to methods using ferromagnetic resonance, this technique offers a faster and more convenient way to determine the spatial distribution of the h-field, which can be used for MW integrated circuit optimization and fault diagnosis.

Aggregation of One-Dimensional Wires: The Case of Long Oligoynes.

We show an unexpected aggregation phenomenon of a long oligoyne (Py[16]) with 16 contiguous triple bonds and endcapped with bulky 3,5-bi(3,5-bis-tert-butylphenyl)pyridine groups. Aggregation of 1D π-conjugated oligoyne chains is rare given the minimal π-π intermolecular interactions as well as its flexibility that works against self-assembly. In dilute solutions, the reversible aggregation of Py[16] initiates at low temperature in the range of 140-180 K, and is not observed for shorter oligoynes in this series. Cryogenic UV/Vis electronic absorption spectra and vibrational Raman spectra with different laser wavelength lines tuning from in-resonance to off-resonance conditions have been used to extract the vibrational features characterizing the monomer and aggregate species. Theoretical calculations complement the spectroscopic findings.

Near-field induced local excitation dynamics of Na10 and Na10-N2 from real-time TDDFT.

Electron dynamics of the Na10 chain and the Na10-N2 complex locally excited by an atomistic optical near-field are investigated using real-time time-dependent density functional theory calculations on real-space grids. Ultrafast laser pulses were used to simulate the near-field excitation under on- and off-resonance conditions. Off-resonance excitation did not lead to the propagation of the excitation through the Na10 chain. In contrast, under the resonance conditions, the excited state is delocalized over the entire Na chain. Analysis of the local dipole moment of each atom in Na10 indicates that this behavior is consistent with the transition density. Adding an N2 molecule to the opposite end of the local excitation region results in energy transfer via the Na10 chain. The energy transfer efficiency of the N2 molecule is well correlated with the absorption spectrum of Na10. The present study paves the way for realizing remote excitation and photonic devices at the atomic scale.

Fast entangling quantum gates with almost-resonant modulated driving

Recently, the method of using a special category of synthetic analytical pulses under off-resonant conditions has improved the experimental performance of two- and multi-qubit gates in the cold atom qubit platform. In order to explore more possibilities and wider ranges of options, we design and analyze the method of almost-resonant modulated driving (ARMD) in constructing fast-speed and high-fidelity quantum logic gates. Whilst the modulation forms the key concept of high-fidelity Rydberg blockade gates so far, the on-off resonance condition can lead to nontrivial nuances in the styles of dynamics, and the ARMD gate protocols have its different characteristic mechanisms in quantum physics compared with the off-resonant gate processes. In particular, ARMD gates usually have abrupt phase changes and at certain points during the time evolution. From a more fundamental point of view, both the resonant and off-resonant methods all together belong to the unitary operation family of fast modulated driving with respect to precisely characterized inter-qubit interactions, which usually allows the quantum logic gate to conclude within one continuous pulse. We anticipate the ARMD gates to work well with the Rydberg dipole-dipole interaction and will serve as a helpful tool in the future studies of the cold atom qubit platform.

GaAs-on-insulator ridge waveguide nanobeam cavities with integrated InAs quantum dots

This study investigates nanobeam cavities on a GaAs-on-insulator (GaAsOI) chip with InAs quantum dots (QDs), including design, fabrication, and experimental characterization. The nanobeam cavities are optimized for high photon coupling efficiency and pronounced light-matter interaction. Numerical studies yield Q factors up to about 1400, a coupling efficiency of nearly 70 % and a maximum Purcell factor of approximately 100. Experimentally, these devices have a Q factor of about 1300, and comparing the lifetime of QDs in on-resonance and off-resonance conditions, a Purcell factor of 10.46±0.14 is obtained. Moreover, in the single-emitter regime, we observe strong multiphoton suppression with g(2)(0)=0.297 . Our results demonstrate the high potential of nanobeam cavities on a GaAsOI platform for quantum photonic applications.

Consequences of Vibrational Strong Coupling on Supramolecular Polymerization of Porphyrins.

Supramolecular polymers display interesting optoelectronic properties and, thus, deploy multiple applications based on their molecular arrangement. However, controlling supramolecular interactions to achieve a desirable molecular organization is not straightforward. Over the past decade, light-matter strong coupling has emerged as a new tool for modifying chemical and material properties. This novel approach has also been shown to alter the morphology of supramolecular organization by coupling the vibrational bands of solute and solvent to the optical modes of a Fabry-Perot cavity (vibrational strong coupling, VSC). Here, we study the effect of VSC on the supramolecular polymerization of chiral zinc-porphyrins (S-Zn) via a cooperative effect. Electronic circular dichroism (ECD) measurements indicate that the elongation temperature (Te) of the supramolecular polymerization is lowered by ∼10 °C under VSC. We have also generalized this effect by exploring other supramolecular systems under strong coupling conditions. The results indicate that the solute-solvent interactions are modified under VSC, which destabilizes the nuclei of the supramolecular polymer at higher temperatures. These findings demonstrate that the VSC can indeed be used as a tool to control the energy landscape of supramolecular polymerization. Furthermore, we use this unique approach to switch between the states formed under ON- and OFF-resonance conditions, achieved by simply tuning the optical cavity in and out of resonance.

Boosting energy harvesting of fully flexible magnetoelectric composites of PVDF-AlN and NiO-decorated carbon nanofibers

The increasing popularity of wearable electronics has sparked interest in flexible energy harvesters as alternatives to conventional batteries. Flexible magnetoelectric (ME) composites, known for converting ambient magnetic field energy into useable power, are emerging as promising autonomous energy sources for integration into wearable devices. In this study, we prepared flexible (PVDF-AlN)–(NiO–CNF) based ME composites using two different methods: solution-casting and electrospinning techniques. The ME coupling was confirmed by measuring the ferroelectric and magnetic properties of the composite, and it was qualitatively characterized through the ME coupling coefficient. The electrospinning fibers-based ME composite exhibited an optimal value of 10.6 V/cm.Oe, significantly higher than the solution-casting films-based ME composite (1.3 V/cm.Oe) under a 1 kHz AC magnetic field (off-resonance condition). Subsequently, a flexible magneto-mechano-electric (MME) generator was designed using electrospun-derived material, harvesting a sinusoidal wave with a maximum output peak-to-peak voltage of 9.02 V. The generator displayed an optimal DC power density of 97 μW/m2 when exposed to a weak AC magnetic field of 6 Oe at a frequency of 50 Hz. Consequently, it holds great promise as an efficient autonomous power supply for medical sensing and various miniature electronic applications.

Manipulation of photosynthetic energy transfer by vibrational strong coupling.

Uncovering the mystery of efficient and directional energy transfer in photosynthetic organisms remains a critical challenge in quantum biology. Recent experimental evidence and quantum theory developments indicate the significance of quantum features of molecular vibrations in assisting photosynthetic energy transfer, which provides the possibility of manipulating the process by controlling molecular vibrations. Here, we propose and theoretically demonstrate efficient manipulation of photosynthetic energy transfer by using vibrational strong coupling between the vibrational state of a Fenna-Matthews-Olson (FMO) complex and the vacuum state of an optical cavity. Specifically, based on a full-quantum analytical model to describe the strong coupling effect between the optical cavity and molecular vibration, we realize efficient manipulation of energy transfer efficiency (from 58% to 92%) and energy transfer time (from 20 to 500ps) in one branch of FMO complex by actively controlling the coupling strength and the quality factor of the optical cavity under both near-resonant and off-resonant conditions, respectively. Our work provides a practical scenario to manipulate photosynthetic energy transfer by externally interfering molecular vibrations via an optical cavity and a comprehensible conceptual framework for researching other similar systems.

Exploring the impact of vibrational cavity coupling strength on ultrafast CN + c-C6H12 reaction dynamics

Abstract Molecular polaritons, hybrid light-matter states resulting from strong cavity coupling of optical transitions, may provide a new route to guide chemical reactions. However, demonstrations of cavity-modified reactivity in clean benchmark systems are still needed to clarify the mechanisms and scope of polariton chemistry. Here, we use transient absorption to observe the ultrafast dynamics of CN radicals interacting with a cyclohexane (c-C6H12) and chloroform (CHCl3) solvent mixture under vibrational strong coupling of a C–H stretching mode of c-C6H12. By modulating the c-C6H12:CHCl3 ratio, we explore how solvent complexation and hydrogen (H)-abstraction processes proceed under collective cavity coupling strengths ranging from 55 to 85 cm−1. Reaction rates remain unchanged for all extracavity, on-resonance, and off-resonance cavity coupling conditions, regardless of coupling strength. These results suggest that insufficient vibrational cavity coupling strength may not be the determining factor for the negligible cavity effects observed previously in H-abstraction reactions of CN with CHCl3.

Kiosk 8R-TC-09 - T2* Mapping of Intramyocardial Hemorrhage: Mitigating the Effects of Off-resonant Conditions in Phantoms and Explanted Heart Tissue

Kiosk 8R-TC-09 - T2* Mapping of Intramyocardial Hemorrhage: Mitigating the Effects of Off-resonant Conditions in Phantoms and Explanted Heart Tissue

Gold-coated porous silicon as a SERS substrate for near-infrared excitation: Off- and on-resonant conditions

Porous silicon, being one of the most popular SERS-active substrates, was in this work utilized for near-infrared 1064 nm excitation which minimizes the radiation-induced degradation of molecules. The production of porous silicon photonic crystals and deposition of gold nanoparticles, as the two possible methods for quenching the crystal silicon band-gap photoluminescence, were thoroughly discussed. For the off-resonant laser excitation conditions, gold nanoparticles were grown on porous silicon by the immersion plating procedure. For the on-resonant conditions, gold nanorods with the appropriate aspect ratio were synthesized by a seed-mediated protocol and deposited on the porous silicon surface. The capability of these metal-dielectric substrates toward SERS enhancement was evaluated using crystal violet dye and the advantages and drawbacks of both methods were addressed in detail. The obtained detection limits for the crystal violet dye were in the range between 10−7 and 10−8 M. So far, gold-coated porous silicon SERS-active substrates for near-infrared 1064 nm excitation have not been reported, both for the off- and on-resonant regimes.

Entanglement control in a laser driven single layer graphene system

Abstract In this letter, we have proposed a new model for quantum control of atom photon entanglement in a single layer graphene via von Neumann reduced entropy of entanglement. We consider the effect of terahertz laser field intensity on the degree of entanglement (DEM) in the resonance and off-resonance condition of the applied fields. We also investigate the spatially dependent of the DEM when two applied light becomes standing wave pattern in x and y directions. Our results show that in different parametric conditions, the population of the different states can be controlled and this leads to modifying the DEM of the system.

Development of a novel lead free (CoFe1.9Bi0.1O4/BaTi0.89Sn0.11O3/CoFe1.9Bi0.1O4) magnetoelectric composite via new design strategy

A novel lead free ceramic based magnetoelectric (ME) tri-layered composite with new design strategy has been fabricated by using sol-gel synthesized Bi3+ doped CoFe2O4 and Sn4+ doped BaTiO3. Structural, microstructural, magnetostriction, piezoelectric and magnetoelectric properties of the synthesized materials and developed system have been thoroughly investigated. CoFe1.9Bi0.1O4 have shown the improvement of magnetostriction (∼259 ppm) and strain sensitivity (∼323 ×10−9 Oe−1) compared to those of un-doped CoFe2O4 (magnetostriction ∼163 ppm and strain sensitivity ∼99 ×10−9 Oe−1). On the other hand, the piezoelectricity of BaTi0.89Sn0.11O3 has improved to 424 pC/N from a value of 194 pC/N for un-doped BaTiO3. The unique design strategy (where the output signal has been collected directly from the piezoelectric layer) and the simultaneous improvement of both the magnetostriction and piezoelectricity of the corresponding components have helped in achieving high ME coupling in the final device. The achievement of high values of in-plane ME coupling coefficients (αME) (α31) at off-resonance and zero-bias resonance conditions (αME ∼49 and 750 mV.cm−1. Oe−1, respectively) have proven the ability of the fabricated device in various potential applications related to magnetic field sensing and magnetoelectric effect.

Off-Resonant Dicke Quantum Battery: Charging by Virtual Photons

We investigate a Dicke quantum battery in the dispersive regime, where the photons trapped in a resonant cavity are much more energetic with respect to the two-level systems embedded into it. Under such off-resonant conditions, even an empty cavity can lead to the charging of the quantum battery through a proper modulation of the matter–radiation coupling. This counterintuitive behaviour has its roots in the effective interaction between two-level systems mediated by virtual photons emerging from the fluctuations of the quantum electromagnetic field. In order to properly characterize it, we address relevant figures of merit such as the stored energy, the time required to reach the maximum charging, and the averaged charging power. Moreover, the possibility of efficiently extracting energy in various ranges of parameters is discussed. The scaling of stored energy and power as a function of the number N of two-level systems and for different values of the matter–radiation coupling is also discussed, showing, in the strong coupling regime, performances in line with what is reported for the Dicke quantum battery in the resonant regime.

Synergy between plasmonic nanocavities and random lasing modes: a tool to dequench plasmon quenched fluorophore emission.

Metal nanoparticles (NPs) can be employed to modify the emission level of a dye emitter by tailoring the spectral overlap of the optical gain and localized surface plasmon resonance (LSPR). In the case of plasmonic random lasers, tuning the spectral overlap by manipulating metal NPs changes the scattering properties of the system, which is crucial in random lasers (RLs). In order to overcome this drawback, the emitter gain spectrum across the LSPR is tuned by appropriately choosing various dye emitters. A system with Au nanoislands (NIs) randomly distributed on the surface of vertically aligned ZnO nanorods on a glass substrate coated with three different dye emitters has been employed to study the metal-gain interaction as a function of spectral overlap. It is observed that the photoluminescence is quenched in the presence of Au NIs for all the three dye emitters; however, the degree of quenching is found to be directly proportional to the extent of spectral overlap of the LSPR and the fluorophore emission spectrum, with the resonantly coupled systems exhibiting higher random lasing thresholds. However, a dequenching of the emission is observed under spectrally off-resonant conditions, leading to a lower threshold RL. The effect of tailoring of the metal-gain interaction on the coherent and incoherent intensity components of RL emission is studied to elucidate the contrasting results of photoluminescence and RL emission. As the optical gain shifts away from the LSPR peak, the RL emission is dominated by the coherent intensity. The speckle-like field distributions of the RL modes couple to the plasmonic nanocavities along with a reduced absorption loss for the off-resonant case, leading to an enhanced stimulated emission. Hence, a synergy between random laser modes, plasmonic nanocavities and optimum spectral overlap has been utilized as a tool to dequench the plasmon quenched fluorophore emission.

Plasmonic quantum nonlinear Hall effect in noncentrosymmetric two-dimensional materials

We investigate an interplay between quantum geometrical effects and surface plasmons through surface plasmonic structures, based on an electron hydrodynamic theory. First we demonstrate that the quantum nonlinear Hall effect can be dramatically enhanced over a very broad range of frequency by utilizing plasmonic resonances and near-field effects of grating gates. Under the resonant condition, the enhancement becomes several orders of magnitude larger than the case without the nanostructures, while the peaks of high-harmonic plasmons expand broadly and emerge under the off-resonant condition, leading to a remarkably broad spectrum. Furthermore, we clarify a universal relation between the photocurrent induced by the Berry curvature dipole and the optical absorption, which is essential for computational material design of long-wavelength photodetectors. Next we discuss a novel mechanism of geometrical photocurrent, which originates from an anomalous force induced by oscillating magnetic fields and is described by the dipole moment of orbital magnetic moments of Bloch electrons in the momentum space. Our theory is relevant to 2D quantum materials such as layered WTe${}_2$ and twisted bilayer graphene, thereby providing a promising route toward a novel type of highly sensitive, broadband terahertz photodetectors.

Driving Third-Order Optical Nonlinearities in Photoluminescent Si Nanoparticles by Nitrogen Co-Implantation in a Silica Matrix.

The photoluminescence and third-order nonlinear optical effects of co-implanted silicon nanoparticles and nitrogen ions in a silica matrix were studied. Experimental evidence shows the potential of nitrogen ions for changing optical properties exhibited by silicon nanoparticles implanted in an integrated system. The modification of the optical bandgap and photoluminescent intensity in the studied nanomaterials by the incorporation of nitrogen was analyzed. Standard two−wave mixing experiments were conducted using nanosecond and picosecond laser pulses at 532 nm wavelength. At this off-resonance condition, only multiphoton excitation can promote electrons at energies above the optical bandgap of the silicon nanoparticles. The picosecond results show that the co-implanted sample with nitrogen exhibits a three-fold enhancement of the nonlinear Kerr response. Femtosecond z-scan measurements were undertaken at 800 nm in order to explore the modification of the ultrafast nonlinear response of the samples that revealed a purely electronic Kerr nonlinearity together to saturable absorption of the SiNPs in the near-infrared. Remarkably, femtosecond results reveal that nitrogen co-implantation in the SiNPs system derives from the quenching of the third-order nonlinear optical behavior. These findings pointed out a simple approach for engineering the optical bandgap of nanocomposites, which can be controlled by a doping process based on ion-implanted nitrogen. It is highlighted that the enhanced light-matter interactions induced by nitrogen implantation can be useful for developing nonlinear integrated silicon photonics nanodevices with low power excitation.

Gold nanoparticles with helical surface structure transformed from chiral molecules for SERS-active substrates preparation

Surface-enhanced Raman scattering (SERS) technique has enlarged the application of Raman spectroscopy, and the most crucial problem is the exploration of SERS-active materials. In the paper, a SERS substrate made of helical gold nanoparticles by the directed synthesis of L-glutathione (L-GSH) was proposed. Because of the large surface specific area and the uneven conduction electrons distribution for sharp tips resulted from the complex concave surface and the symmetry breaking structure, The nanostructure has shown an impressive average enhancement factor (EF) of 2.95 × 105 under off-resonant condition. This phenomenon was explained by the experimental results and finite difference time domain (FDTD) method. Finally, the SERS substrates were used to detect thiram on pear with a limit of detection (LOD) of 0.62 mg/kg and R2 of 0.9772. The proposed SERS substrates suggest the potential application of chiral molecules such as amino acids, peptides et al. in the SERS-active materials fabrication.

Applicability of the Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders in Cross-Flow

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each fin type, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

Synthesis, characterization and nonlinear optical properties of polylactide and PMMA based azophloxine nanocomposites for optical limiting applications

The widespread usage of harmful pulsed laser sources emitting brief but intense radiations implies to search for appropriate and convenient forms of protection. Nonlinear optical nanomaterials can serve this purpose when properly embedded in a solid medium, resulting in nanocomposite passive optical limiting filters.This article focuses on the optical limiting behavior of a series of polymer-dye nonlinear nanocomposites, for which we combined azophloxine, a red azo dye, with two polymer hosts, namely polymethyl methacrylate (PMMA) and polylactide (PLA). In this work, optical filters were produced by chemical synthesis from the bulk. Their linear absorption and transmittance were measured by UV–VIS-NIR spectrophotometry and their thermal examination was done via TGA measurements. The optical limiting properties were characterized using an appropriate custom-made optical setup and the nonlinear absorption coefficients and refractive indices were measured by the Z-scan method. Optical measurements in the nonlinear regime were performed at the wavelength of 1064 nm with nanosecond pulses at a low pulse repetition rate. The nonlinear optical properties resulting from energy dependent transmittance assessments reveal that the dye concentration is of major relevance regarding the PMMA nanocomposites, and to a lesser extend for the PLA based systems. The PLA synthesis concept described in this study offers an easy way to directly attach the dye covalently to the polymer chain. The originality and novelty of this synthesis technique is to be pointed out since it has never been mentioned elsewhere to date. For the various types of nanocomposites investigated, significant differences in the optical limiting response were observed. For instance, it is averred that a significantly higher optical limiting effect results in the systems with the less azo dye concentration and the best optical limiting performance corresponding to a laser protection level of OD = 3.3 was measured for the PLA based system. Besides, the PMMA nanocomposite system exhibits an optical limiting level of OD = 1.9. A molecular model claiming for the dye aggregation in the PMMA nanocomposites is discussed. Two different absorption regimes responsible for the optical limiting action have been identified to be reverse saturable (RSA) – excited state absorption (ESA) on the one hand and multi-photons absorption (MPA) on the other hand. By means of transmittance investigations in an open Z-scan configuration, one could observe the sudden and remarkable changeover from a saturable absorption (SA) regime to a reverse saturable absorption one for high azo dye loads in PMMA. Such transition from SA to RSA has been basically revealed for materials and experimental conditions close to or centered on the resonance of absorption (i.e. around 532 nm). To the author’s knowledge, a study in off-resonant conditions (i.e. 1064 nm) was never reported elsewhere to date. Also tracked out by open Z-scan measurements, significantly higher nonlinear absorption coefficients βresulted for the PLA based systems. Similar experiments in a close aperture Z-scan scheme revealed nonlinear refractive indexes in the order of n2=-2.0X10-15cm2/W for the PMMA nanocomposites and n2=-3.0X10-15cm2/W for the PLA nanocomposites.