Resonant Excitation Conditions Research Articles

Ecofriendly Filtration of Silver Nanoparticles for Ultrasensitive Surface-Enhanced (Resonance) Raman Spectroscopy-Based Detection.

In this study, a widely used colloid of Creighton AgNPs (ORI, 1-100 nm, mostly ≤ 40 nm, ∼10 μg mL-1) was rapidly manipulated via tangential flow filtration (TFF) for highly reproducible surface-enhanced (resonance) Raman spectroscopy (SE(R)RS) experiments down to the single-molecule (SM) level. The quasi-spherical AgNPs were size-selected, purified, and concentrated in two TFF fractions of a cutoff diameter of ∼40 nm: AgNP ≤ 40 (∼900 μg mL-1) and AgNP ≥ 40 (∼100 μg mL-1). The SE(R)S-based sensing capabilities of the two TFF fractions were then tested under pre-resonance (632.8 nm) and resonance (532.1 nm) excitation conditions for rhodamine 6G (R6G, 10-6-10-15 M). Both TFF isolates, AgNP ≤ 40 and AgNP ≥ 40, were more effective in adsorbing the R6G analyte (≥91%) than the original colloid (≥78%) at submonolayer coverages. Furthermore, the surface enhancement factors (SEF) of the two TFF fractions were markedly superior to those of ORI under all excitation conditions. SERS at 632.8 nm: only AgNP ≥ 40 enabled the detection of R6G at 10-9 M and produced the largest SEF (2.1 × 106). SE(R)RS and SM-SERRS at 532.1 nm: AgNP ≥ 40 gave rise to the largest SEF values (2.5 × 1010) corresponding to the SM regime down to 10-15 M of R6G. Nevertheless, AgNP ≤ 40 compensated for the size-dependence of the electromagnetic enhancements by an increase in the silver concentration, which led to SEF values comparable to those of AgNP ≥ 40 through additional resonance enhancements. TFF resulted into a ∼100-fold increase (AgNP ≤ 40) in the number of negatively charged AgNPs that were available to electrostatically bridge R6G cations and form SERRS "hot-spots" (AgNP-R6G-AgNP) within the focal volume. Evidently, the interplay between AgNP size, AgNP concentration, and excitation wavelength governs the SE(R)RS enhancements. This study demonstrated that TFF can facilitate the ecofriendly isolation of spherical AgNPs of controlled morphological and plasmonic properties for further enhancing their sensing capabilities as SE(R)RS substrates.

Discovering Love numbers through resonance excitation during extreme mass ratio inspirals

General Relativity predicts that black holes (BHs) do not possess an internal structure and consequently cannot be excited. This leads to a specific prediction about the waveform of gravitational waves (GWs) which they emit during a binary BH inspiral and to the vanishing of their Love numbers. However, if astrophysical BHs do possess an internal structure, their Love numbers would no longer vanish, and they could be excited during an inspiral by the transfer of orbital energy. This would affect the orbital period and lead to an observable imprint on the emitted GWs waveform. The effect is enhanced if one of the binary companions is resonantly excited. We discuss the conditions for resonant excitation of a hypothetical internal structure of BHs and calculate the phase change of the GWs waveform that is induced due to such resonant excitation during intermediate- and extreme-mass-ratio inspirals. We then relate the phase change to the electric quadrupolar Love number of the larger companion, which is resonantly excited by its smaller companion. We discuss the statistical error on measuring the Love number by LISA and show that, because of this phase change, the statistical error is small even for values of the Love number as small as 10−4 for moderate values of the spin parameter. Our results indicate that, for extreme-mass-ratio inspirals with moderate spin parameter, the Love number could be detected by LISA with an accuracy which is higher by up to two orders of magnitude than what can be achieved via tidal deformation effects. Thus, our results indicate that resonant excitation of the central BH during an extreme- or intermediate-mass-ratio inspirals is the most promising effect for putting bounds on, or detecting, non-vanishing tidal Love numbers of BHs.

Ion parking in native mass spectrometry.

A forced, damped harmonic oscillator model for gas-phase ion parking using single-frequency resonance excitation is described and applied to high-mass ions of relevance to native mass spectrometry. Experimental data are provided to illustrate key findings revealed by the modelling. These include: (i) ion secular frequency spacings between adjacent charge states of a given protein are essentially constant and decrease with the mass of the protein (ii) the mechanism for ion parking of high mass ions is the separation of the ion clouds of the oppositely-charged ions with much less influence from an increase in the relative ion velocity due to resonance excitation, (iii) the size of the parked ion cloud ultimately limits ion parking at high m/z ratio, and (iv) the extent of ion parking of off-target ions is highly sensitive to the bath gas pressure in the ion trap. The model is applied to ions of 17 kDa, 467 kDa, and 2 MDa while experimental data are also provided for ions of horse skeletal muscle myoglobin (≈17 kDa) and β-galactosidase (≈467 kDa). The model predicts and data show that it is possible to effect ion parking on a 17 kDa protein to the 1+ charge state under trapping conditions that are readily accessible with commercially available ion traps. It is also possible to park β-galactosidase efficiently to a roughly equivalent m/z ratio (i.e., the 26+ charge state) under the same trapping conditions. However, as charge states decrease, analyte ion cloud sizes become too large to allow for efficient ion trapping. The model allows for a semi-quantitative prediction of ion trapping performance as a function of ion trapping, resonance excitation, and pressure conditions.

Лабораторная работа «Изучение многофотонной ионизации в условиях резонансного возбуждения атомарных паров»

The developed laboratory work is described, designed to study multiphoton ionization under conditions of resonant excitation of atomic vapors by frequency-tunable laser radiation. Atomic pairs of potassium and rubidium were chosen as objects of study. To demonstrate the resonant nature of multiphoton ionization, the results of studies of the dependence of the magnitude of the ion signal on the frequency of laser radiation causing this signal are presented. Analytical expressions are given to describe the experimentally observed patterns of resonant ionization processes. Laboratory work is part of a set of works on the study of resonant nonlinear optics for students studying physics at universities.

Plasmonically coupled semiconductor quantum dots for efficient hydrogen photoelectrocatalysis

Photocatalytic water splitting has attracted significant attention as a low-cost, clean, and green method for the conversion of solar energy into hydrogen, highlighting its potential to solve energy and environmental problems. In this work, we report the coupling of a plasmonic resonator with semiconductor quantum dots (QDs) for enhancement in photoelectrocatalytic water splitting toward hydrogen (H2) production. Specifically, cadmium selenide (CdSe) QDs were deposited on silver nano-gratings (Ag gratings). Plasmonic enhancement was observed in the absorption/emission of QDs using our angle-resolved steady-state optical spectroscopy. Furthermore, angle-resolved absorption spectra helped us to optimize the illumination conditions for resonant excitation using a setup for photoelectrochemical (PEC) experiments. Under the resonant pump, the emission of the QDs has been plasmonically enhanced with a Purcell factor (FP) of ∼1.5. Our numerical simulation revealed a strong near-field enhancement due to the excitation of surface plasmon resonances, contributing to FP. A similar enhancement order in the PEC experiments was also observed under resonant pump conditions, indicating the contribution of plasmon resonances to the enhanced photoelectrocatalysis. Switching the excitation's polarization further reinforces this, resulting in an enhanced photocurrent under p-polarization. These findings provide a proof of concept, thus laying the foundation for a practical device for efficient solar-to-H2 conversion.

Multi-zone resonance spectrometry of inelastic electron scattering of light and the manifestation of strong spin-orbit interaction in nanostructures with quantum dots

Highly sensitive methods of inelastic light scattering spectrometry have been developed to detect individual photons in the visible and near-infrared spectral ranges (0.4-1.35) μm. Precision optical measurements of vibrational and electronic states of nanostructures with quantum objects are performed, using the example of quantum-dimensional nanoheterostructures (311)In si-GaAs/InAs with InAs quantum dots. A distinctive attractive feature of such structures with a degenerate valence band of symmetry 8 is the presence of a strong spin-orbit interaction. In this case, the intrinsic moment of the holes can effectively interact with the electric field of the incident light wave. It was found that such interaction causes intense luminescence and inelastic scattering of the light wave in the IR region of the 0.9-1.35 μm spectrum. Effective generation of nonequilibrium electron-hole (e-h) plasma with concentrations n=p=1.0·1017 cm-3 and T_e=T_h=25 K,was revealed under resonant excitation conditions, while the lattice temperature T_L=5.1 K. New mechanisms have been discovered for the formation of an abnormally intense integration spectrum of multiplex inelastic light scattering of a rather complex shape formed by various separable resonant contributions of the processes of quasi-elastic scattering by charge carriers, light scattering by acoustic plasmons of electron-hole plasma, as well as inelastic intra- and inter-band light scattering by heavy holes. It has been established that the anomalous intensity gain of such multi-zone selective resonant light scattering is more than 105 times higher than the intensity of Thomson light scattering on individual charge carriers. There is agreement between the estimated calculated and experimental spectra, and for the most part for the difficult-to-interpret significant width of the observed light scattering line. It is shown that new mechanisms of various contributions to the formation of scattered photon radiation are important diagnostic elements that are clearly manifested in the spectra of the resulting enhanced inelastic light scattering. Keywords: nanostructures, quantum objects, resonant scattering of light by charge carriers, exchange interaction, plasma diagnostics.

Layered topological semimetal GaGeTe: New polytype with non-centrosymmetric structure

GaGeTe is a layered van der Waals material composed of germanene and GaTe sublayers that has been recently predicted to be a basic Z2 topological semimetal. To date, only one polytype of GaGeTe is known with trigonal centrosymmetric structure (α phase, space group R-3m, No. 166). Here we show that as-grown samples of GaGeTe show traces of at least another polytype with hexagonal non-centrosymmetric structure (β phase, space group P63mc, No. 186). Moreover, we suggest that another bulk hexagonal polytype (γ phase, space group P-3m1, No. 164) could also be found near room conditions. Both α and β polytypes have been identified and characterized by means of X-ray diffraction and Raman scattering measurements with the support of ab initio calculations. We provide the vibrational properties of both polytypes and show that the Raman spectrum reported for GaGeTe almost forty years ago and attributed to the α phase, was, in fact, that of the secondary β phase. Additionally, we show that a Fermi resonance occurs in α-GaGeTe under non-resonant excitation conditions, but not under resonant excitation conditions. Theoretical calculations show that bulk β-GaGeTe is a non-centrosymmetric weak topological semimetal with even smaller lattice thermal conductivity than centrosymmetric bulk α-GaGeTe. In perspective, our work paves the way for the control and engineering of GaGeTe polytypes to design and implement complex van der Waals heterostructures formed by a combination of centrosymmetric and non-centrosymmetric layers of up to three different polytypes in a single material, suitable for a number of fundamental studies and technological applications.

Integrating-Sphere-Assisted Resonance Synchronous Spectroscopy for the Quantification of Material Double-Beam UV-Vis Absorption and Scattering Extinction.

Integrating spheres (IS) have been used extensively for the characterization of light absorption in turbid samples. However, converting the IS-based sample absorption coefficient to the UV-vis absorbance quantified with a double-beam UV-vis spectrophotometer is challenging. Herein, we report an integrating-sphere-assisted resonance synchronous (ISARS) spectroscopy method performed with conventional spectrofluorometers equipped with an integrating-sphere accessory. Mathematical models and experimental procedures for quantifying the sample, solvent, and instrument-baseline ISARS intensity spectra were provided. A three-parameter analytical model has been developed for correlating the ISARS-based UV-vis absorbance and the absorbance measured with double-beam instruments. This ISARS method enables the quantitative separation of light absorption and scattering contribution to the sample UV-vis extinction spectrum measured with double-beam UV-vis spectrophotometers. Example applications of this ISARS technique are demonstrated with a series of representative samples differing significantly in their optical complexities, from approximately pure absorbers, pure scatterers, to simultaneous light absorbers, scatterers, and emitters under resonance excitation and detection conditions.

Resonant absorption in an inhomogeneous disordered metamaterial: First-principles simulation

In this study, we perform first-principles simulations of the resonant excitation of plasmalike oscillations in a two-dimensional inhomogeneous disordered metamaterial. The oscillations are initiated by an oblique incidence of a linearly polarized electromagnetic wave. The conditions for resonant excitation are satisfied near the point where the real part of the effective permittivity of the metamaterial changes sign from positive to negative and crosses zero. First, the problem was analyzed in the framework of the effective medium approximation, which predicts a resonant growth of the electric field and associated resonant absorption near the interface between positive and negative permittivity. It was shown that an array of point dipoles can sustain plasmalike waves near the zero of the effective permittivity. In order to trace the appearance of such a mode at the microscopic scale, full-scale first-principles simulations of a two-dimensional metamaterial with a randomly generated distribution and a linearly increasing average concentration of meta-atoms were performed. The results of the simulations were compared to the predictions of the effective medium approximation. The influence of the fluctuations in the meta-atom concentration on the excitation of the field oscillations and the resonant absorption was quantified.

Excitation of high-intensity terahertz surface modes of plasma slab under action of p-polarized two-frequency laser radiation.

The excitation of the terahertz (THz) high-intensity surface modes when the two-frequency p-polarized laser radiation interacts with a plasma slab is studied. It was found that the significant amplification of the laser field in the plasma slab occurs when p-polarized laser radiation is incident at the angle of total reflection. It is shown that, under the action of laser radiation ponderomotive forces, the resonant excitation of the THz mode of the plasma slab occurs if the frequency difference of the laser fields coincides with the eigenfrequency of the surface mode. It is established that the giant increase in the energy flux density of the THz mode occurs when p-polarized laser radiation is incident at the angle of total reflection on the near-critical plasma slab with rare electron collisions if the conditions of resonant excitation are satisfied. It is shown that in this case the energy flux density of THz mode can significantly exceed the laser intensity.

High harmonics generation in gases near the gratings: towards the spectrum enhancement and enrichment

The problem of harmonic generation efficiency (as an example of non-linear optical phenomena) increasing by atomic media near the surface of a one-dimensional metal diffraction grating under conditions of plasmon resonance excitation is considered. The local field enhancement factor dependences on diffraction grating profile are studied. Spatial distribution of the femtosecond pulse electric field strength over the grating surface under conditions of plasmon resonance excitation is simulated. Generated harmonic efficiency enhancement and photoemission spectra enrichment (due to laser field strength amplification near the grating) are discussed.

Low-frequency resonance in laminated FeGa-FeCoGa/Metglas/PZT structures

The paper studies the influence of the composition of a thin-film composite magnetostrictive ferromagnet on the magnetoelectric effect (ME) in ferromagnet/piezoelectric/ferromagnet laminated trilayers at resonant frequencies. The PZT material was used in the piezoelectric layer. The graded composite magnetostrictive ferromagnet with a thickness gradient of the magnetostriction coefficient was obtained by pulsed laser deposition of thin Fe0.72Ga0.28 or Fe0.62Co0.19Ga0.19 films on the surface of Metglas-type 440A amorphous ribbons. The ME was investigated at resonant frequencies of 3 and 9.32 kHz. It is shown that the maximum ME value increases with frequency. The deposition of magnetostrictive thin films decreases the maximum ME value, but increases the Q-factor. The results can be useful for developing sensors of static and low-frequency magnetic fields for magnetic nondestructive testing applications under resonant excitation conditions.

Combining Chemical Knowledge and Quantum Calculation for Interpreting Low-Energy Product Ion Spectra of Metabolite Adduct Ions: Sodiated Diterpene Diester Species as a Case Study.

We investigated the product ion spectra of [M + Na]+ from diterpene diester species and low molecular mass metabolites analyzed by electrospray ionization (ESI). Mainly, the formation of protonated salt structures was proposed to explain the observed neutral losses of carboxylic acids. It also facilitates understanding sodium retention on product ions or on neutral losses. In addition, the occurrence of consecutive carboxylic acid losses is rather unexpected under resonant excitation conditions. Quantum calculation demonstrated that the exothermic character of such neutral losses can represent a relevant explanation. There is no doubt that the formation and role of the protonated salt structures will be helpful for a better understanding and software-assisted interpretation of tandem mass spectra from small molecules, especially in the ever-growing metabolomics field.

Role of dark exciton states in the relaxation dynamics of bright 1s excitons in monolayer WSe2

Monolayer transition metal dichalcogenides (1L-TMDs) are excellent platforms for exciton physics. In tungsten-based 1L-TMDs, the existence of dark excitons at lower energy has important roles for bright exciton relaxation. However, the detailed relaxation dynamics from bright to dark excitons have not been revealed sufficiently. In this paper, we studied the rise dynamics of out-of-plane polarized photoluminescence (PL) from spin-forbidden dark excitons in monolayer WSe2. Under conditions of resonant excitation to the bright 1s excitons, PL from the spin-forbidden dark exciton has a finite rise time of a few tens of picoseconds, which suggests that intermediate states, probably hot indirect dark excitons, should play an important role in the relaxation pathway from the bright to the spin-forbidden dark excitons. The excitation density dependence indicates that exciton–exciton scattering should promote faster relaxation to the spin-forbidden dark excitons.

Broadband SERS Enhancement by DNA Origami Assembled Bimetallic Nanoantennas with Label-Free Single Protein Sensing.

Engineering hotspots in surface-enhanced Raman spectroscopy (SERS) through precisely controlled assembly of plasmonic nanostructures capable of expanding intense field enhancement are highly desirable to enhance the potentiality of SERS as a label-free optical tool for single molecule detection. Inspired by DNA origami technique, we constructed plasmonic dimer nanoantennas with a tunable gap decorated with Ag-coated Au nanostars on origami. Herein, we demonstrate the single-molecule SERS enhancements of three dyes with emission in different spectral regions after incorporation of single dye molecules in between two nanostars. The enhancement factors (EFs) achieved in the range of 109-1010 for all the single dye molecules, under both resonant and nonresonant excitation conditions, would enable enhanced photostability during time-series measurement. We further successfully explored the potential of our designed nanoantennas to accommodate and detect a single thrombin protein molecule after selective placement in the wide nanogap of 10 nm. Our results suggest that such nanoantennas can serve as a broadband SERS enhancer and enable specific detection of target biological molecules with single-molecule sensitivity.

Between plasmonics and surface-enhanced resonant Raman spectroscopy: toward single-molecule strong coupling at a hotspot.

The purpose of this minireview is to build a bridge between two research fields: surface-enhanced resonant Raman spectroscopy (SERRS) under near-single-molecule conditions and the branch of plasmonics treating strong coupling between plasmons and molecular excitons. SERRS enables single-molecule spectroscopy owing to its significant enhancement at SERRS hotspots (HSs), localized at gaps or junctions between plasmonic nanoparticle aggregates. SERRS is SERS (surface enhanced Raman spectroscopy) under a resonant Raman excitation condition. The origin of the Raman enhancement in SERRS is electromagnetic coupling between plasmons and molecular excitons at HSs. It has been reported that the coupling energy at HSs reaches the strong coupling region, meaning that they are potential platforms for applications of single molecular excitons modified by strong coupling. In this review, we discuss recent progress related to electronic strong coupling in near-single-molecule SERRS: collective (e.g., vibrational) strong coupling is out of the scope of this minireview. First, we explain the relationship between the electromagnetic enhancement factor and coupling energy. Second, we introduce three theoretical methods for obtaining evidence of strong coupling at HSs. Third, we discuss a method for reproducing enhanced and modified molecular Raman and fluorescence spectra at HSs using the coupling energy. Finally, we propose the use of two experimental methods of absorption spectroscopy at HSs for modifying molecular electronic dynamics by strong coupling and comment on future applications of SERRS HSs to photophysics and photochemistry.

Direct high-resolution resonant Raman scattering measurements of dynamic nuclear spin polarization states of an InAs quantum dot

We report on the direct measurement of the electron spin splitting and the accompanying nuclear Overhauser (OH) field, and thus the underlying nuclear spin polarization (NSP) and fluctuation bandwidth, in a single InAs quantum dot under resonant excitation conditions with unprecedented spectral resolution. The electron spin splitting is measured directly via resonant spin-flip single photon Raman scattering detected by superconducting nanowires to generate excitation-emission energy maps. The observed two-dimensional maps reveal an OH field that has a non-linear dependence on excitation frequency. This study provides new insight into earlier reports of so-called avoidance and tracking, showing two distinct NSP responses directly by the addition of a emission energy axis. The data show that the polarization processes depend on which electron spin state is optically driven, with surprising differences in the polarization fluctuations for each case: in one case, a stabilized field characterized by a single-peaked distribution shifts monotonically with the laser excitation frequency resulting in a nearly constant optical interaction strength across a wide detuning range, while in the other case the previously reported avoidance behavior is actually the result of a nonlinear dependence on the laser excitation frequency near zero detuning leading to switching between two distinct mesoscopic nuclear spin states. The magnitude of the field, which is as large as 400 mT, is measured with sub-100 nuclear spin sensitivity. Stable/unstable points of the OH field distribution are observed, resulting from the non-linear feedback loop in the electron-trion-nuclear system. Nuclear spin polarization state switching occurs between fields differing by 160 mT at least as fast as 25 ms. Control experiments indicate that the strain-induced quadrupolar interaction may explain the measured OH fields.

Sensitivity Features of Double-Resonance Plasmonic Sensor

The paper presents the results of a model investigation about the temporal dynamics of changes in the resonance excitation conditions of surface plasmon-polariton waves in a double-resonance plasmonic sensor at different thicknesses of the sensitive ligand layer. It was shown that the maximum sensor reaction rate to the emergence of analyte is observed at a ligand layer with 40–50 nm thickness. When the ligand layer thickness is less than 40 nm, the sensitivity of the sensor decreases sharply, and when the ligand thickness is increase over 60 nm, a delay in the sensor reaction is observed which due to the limited diffusion rate of the analyte into the ligand. The most effective mode of a plasmon sensor operation is the mode in which the angle of the exciting beam incidence is somewhat different from the resonance angle at condition when the analyte is absent.

Biexciton initialization by two-photon excitation in site-controlled quantum dots: The complexity of the antibinding state case

In this work, we present a biexciton state population in (111)B oriented site-controlled InGaAs quantum dots (QDs) by resonant two photon excitation. We show that the excited state recombines emitting highly pure single photon pairs entangled in polarization. The discussed cases herein are compelling due to the specific energetic structure of pyramidal InGaAs QDs—an antibinding biexciton—a state with a positive binding energy. We demonstrate that resonant two-photon excitation of QDs with antibinding biexcitons can lead to a complex excitation-recombination scenario. We systematically observed that the resonant biexciton state population is competing with an acoustic-phonon assisted population of an exciton state. These findings show that under typical two-photon resonant excitation conditions, deterministic biexciton state initialization can be compromised. This complication should be taken into account by the community members aiming to utilize similar epitaxial QDs with an antibinding biexciton.

Quantification of the Optical Properties of Perovskite Nanocrystals Using a Combination of Polarized Resonance Synchronous and Polarized Anti-Stokes, On-Resonance, and Stokes-Shifted Spectroscopy

Reliable quantification of the optical properties of perovskite nanocrystals (PNCs) is necessary for rational PNC design and applications in optoelectronics. Presented herein is the experimental evaluation of the photon scattering, absorption, and on-resonance fluorescence (ORF) cross sections of lead halide PNCs. Four CsPbX3 (X = Cl, Br, or I) PNCs fabricated through anion exchanges with the same parent PNC CsPbCl3 were studied using UV–vis, fluorescence, polarized resonance synchronous spectroscopic (PRS2), and the polarized anti-Stokes-shifted, on-resonance, and Stokes-shifted (PAOS) spectroscopic methods. All of the PNCs exhibit strong ORF in the wavelength region where the PNC absorption and fluorescence spectra overlap. The PNC optical properties under resonance excitation and detection conditions differ in different wavelength regions. They are simultaneous light absorbers and scatterers in the wavelength region shorter than the blue-edge wavelength of the PNC ORF peak; simultaneously, photon absorbers, scatterers, and emitters in the wavelength region where the PNC is ORF active; and light scatterers alone in the wavelength region longer than the red-edge wavelength of the PNC ORF peak. The PNC peak ORF wavelength and absorption extinction cross section increase with increasing fraction of heavy halides. However, the ORF cross section and quantum yield (QY) of the iodide-containing PNCs are several folds lower than those of their counterpart iodide-free PNCs. The effects of sample aging on the PNC optical properties have been quantified in terms of PNC absorption, scattering, and ORF cross sections and ORF QY. In addition to providing a series of quantitative information not accessible before, we anticipate that the devised methodology will be extended to fluorescent nanomaterials for which the existing tools are inadequate for decoupling the complex interplay among light UV–vis absorption, scattering, and fluorescence emission that can concurrently occur under the same excitation and detection conditions.