Multistep Excitation Research Articles

General model of nonradiative excitation energy migration on a spherical nanoparticle with attached chromophores

Theory of multistep excitation energy migration within the set of chemically identical chromophores distributed on the surface of a spherical nanoparticle is presented. The Green function solution to the master equation is expanded as a diagrammatic series. Topological reduction of the series leads to the expression for emission anisotropy decay. The solution obtained behaves very well over the whole time range and it remains accurate even for a high number of the attached chromophores. Emission anisotropy decay depends strongly not only on the number of fluorophores linked to the spherical nanoparticle but also on the ratio of critical radius to spherical nanoparticle radius, which may be crucial for optimal design of antenna-like fluorescent nanostructures. The results for mean squared excitation displacement are provided as well. Excellent quantitative agreement between the theoretical model and Monte–Carlo simulation results was found. The current model shows clear advantage over previously elaborated approach based on the Padé approximant.

Multi-step laser excitation of the highly excited 5snf 1F3 states of cadmium

We report excitation energies, term energies and effective quantum numbers n of the 5snf 1F3 Rydberg series of cadmium from n = 14 to 45 using a three-step laser excitation scheme via the 5s5d 1D2 intermediate state. The experiment was performed using three dye lasers simultaneously pumped by the second (532 nm) and third (355 nm) harmonics of a Q-switch Nd: YAG laser in conjunction with an atomic beam setup. A two-parameter fit to the transition energies of the 5snf 1F3 series yields the binding energy of the 5s5d 1D2 level as 13,320.33 ± 0.03 cm−1 and consequently the first ionization potential of cadmium is determined as 72,540.06 ± 0.15 cm−1, which is in good agreement with the previously reported values.

Multistep Coulomb excitation of Ni64 : Shape coexistence and nature of low-spin excitations

The structure of $^{64}\mathrm{Ni}$, the heaviest stable Ni isotope, has been investigated via high-statistics, multistep safe Coulomb excitation to search for shape coexistence, a phenomenon recently observed in neutron-rich $^{66}\mathrm{Ni}$ and $^{70}\mathrm{Ni}$ as well as in doubly magic, $N=40, ^{68}\mathrm{Ni}$. The study was motivated by recent, state-of-the-art Monte Carlo shell-model calculations (MCSM), where a Hamiltonian with effective interactions incorporating the monopole tensor force predicts the existence of shape coexistence, also in the lower-mass $^{62,64}\mathrm{Ni}$ isotopes. A set of transition and static $E2$ matrix elements for both yrast and near-yrast structures was extracted from the differential Coulomb excitation cross sections. From comparisons between the new results and MCSM as well as other shell-model calculations, a clearer picture of the structure of $^{64}\mathrm{Ni}$ emerges. Specifically, the low-spin states are shown to be dominated by proton and neutron excitations mainly within the $fp$ shell, with minimal contribution from the ${g}_{9/2}$ shape-driving neutron orbital. The agreement between experimental data and MCSM results indicates a small oblate deformation for the ${0}_{2}^{+}$ level and a spherical shape for the ${0}_{3}^{+}$ state. In addition, the small upper limit determined for the $B(E2)$ probability of a transition associated with the decay of the recently observed 3463-keV, ${0}_{4}^{+}$ state agrees with its proposed assignment to a prolate shape, herewith providing first evidence for triple shape coexistence in a stable Ni isotope.

E2 rotational invariants of [formula omitted] and [formula omitted] states for 106Cd: The emergence of collective rotation

The collective structure of 106Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/A beam of 106Cd on a 1.1 mg/cm2208Pb target using GRETINA-CHICO2 at ATLAS. Fourteen E2 matrix elements were obtained. The nucleus 106Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of E2 matrix elements. The 〈02+||E2||21+〉 matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, 〈Q2〉, of the first-excited 21+ level relative to the 01+ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in 114Cd by C. Fahlander et al. (1988) [38], which is complicated by low-lying shape coexistence near midshell.

Modeling results on the dust charge distribution in a plasma afterglow

Discharging of dust particles in an argon plasma afterglow is investigated using different approaches. First, the dust charge distribution function (DCDF) is obtained by solving numerically the master equation describing dust discharging as a one-step stochastic process. Second, the DCDF is calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. Additionally, the time-dependencies for the mean dust charge are obtained assuming that the charge changes continuously in the afterglow plasma. Calculation results are compared with available experimental data and are found to be in good qualitative agreement if the dust discharging model accounts for the emission of electrons in the collisions of excited argon atoms with dust particles. This study is carried out taking into account the transition from ambipolar to free diffusion as well as multistep ionization, excitation, and deexcitation of argon atoms in the plasma afterglow.

Measurement of Photoionization Cross-Section for the Excited States of Atoms: A Review

A review of experimental studies of the measurement of the photoionization cross-section for the excited states of the alkali atoms, alkaline earth atoms, and rare-gas atoms is presented, with emphasis on using multi-step laser excitation, ionization, and the saturation technique. The dependence of the photoionization cross-section from different intermediate states populated in the first step and ionized in the second step are discussed, including results on the photoionization cross-sections measured above the first ionization threshold. Results based on different polarizations of the exciting and the ionizing dye lasers are also discussed. Examples are provided, illustrating the photoionization cross-sections measured using thermionic diode ion detector, atomic beam apparatus in conjunction with a time-of-flight mass spectrometer and DC/RF glow discharge cell as an optogalvanic detection.

Coulomb excitation of Rn222

The nature of quadrupole and octupole collectivity in Rn222 was investigated by determining the electric-quadrupole (E2) and octupole (E3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive Rn222 beam, accelerated to 4.23 MeV/u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball γ-ray spectrometer following the bombardment of two targets, Sn120 and Ni60. Transition E2 matrix elements within the ground-state and octupole bands were measured up to 10ℏ and the results were consistent with a constant intrinsic electric-quadrupole moment, 518(11)efm2. The values of the intrinsic electric-octupole moment for the 0+→3− and 2+→5− transitions were found to be respectively 2360−210+300efm3 and 2300−500+300efm3 while a smaller value, 1200−900+500efm3, was found for the 2+→1− transition. In addition, four excited non-yrast states were identified in this work via γ−γ coincidences.6 MoreReceived 10 December 2021Accepted 8 February 2022DOI:https://doi.org/10.1103/PhysRevC.105.024323Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsNuclear structure & decaysPropertiesA ≥ 220Nuclear Physics

On the population density of the argon excited levels in a high power impulse magnetron sputtering discharge

Population densities of excited states of argon atoms in a high power impulse magnetron sputtering (HiPIMS) discharge are examined using a global discharge model and a collisional-radiative model. Here, the ionization region model (IRM) and the Orsay Boltzmann equation for electrons coupled with ionization and excited states kinetics (OBELIX) model are combined to obtain the population densities of the excited levels of the argon atom in a HiPIMS discharge. The IRM is a global plasma chemistry model based on particle and energy conservation of HiPIMS discharges. OBELIX is a collisional-radiative model where the electron energy distribution is calculated self-consistently from an isotropic Boltzmann equation. The collisional model constitutes 65 individual and effective excited levels of the argon atom. We demonstrate that the reduced population density of high-lying excited argon states scales with (p*)−6, where p* is the effective quantum number, indicating the presence of a multistep ladder-like excitation scheme, also called an excitation saturation. The reason for this is the dominance of electron impact processes in the population and de-population of high-lying argon states in combination with a negligible electron–ion recombination.

Precision measurement of quasi-bound resonances in H2 and the H + H scattering length

Quasi-bound resonances of are produced via two-photon photolysis of S molecules as reactive intermediates or transition states and detected before decay of the parent molecule into three separate atoms. As was previously reported [K. F. Lai et al., Phys. Rev. Lett. 127, 183001 (2021)] four centrifugally bound quantum resonances with lifetimes of multiple μs, lying energetically above the dissociation limit of the electronic ground state of , were observed as , , , and , while also the short-lived ( ns) quasi-bound resonance was probed. The present paper gives a detailed account on the identification of the quasi-bound or shape resonances, based on laser detection via - two-photon transitions, and their strongly enhanced Franck-Condon factors due to the shifting of the wave function density to large internuclear separation. In addition, the assignment of the rotational quantum number is verified by subsequent multi-step laser excitation into autoionisation continuum resonances. Existing frameworks of full-fledged ab initio computations for the bound region in , including Born-Oppenheimer, adiabatic, non-adiabatic, relativistic and quantum-electrodynamic contributions, are extended into the energetic range above the dissociation energy. These comprehensive calculations are compared to the accurate measurements of energies of quasi-bound resonances, finding excellent agreement. They show that the quasi-bound states are in particular sensitive to non-adiabatic contributions to the potential energy. From the potential energy curve and the correction terms, now tested at high accuracy over a wide range of energies and internuclear separations, the s-wave scattering length for singlet H+H scattering is determined at . It is for the first time that such an accurate value for a scattering length is determined based on fully ab initio methods including effects of adiabatic, non-adiabatic, relativistic and QED with contributions up to .

Laser spectroscopy of indium Rydberg atom bunches by electric field ionization

This work reports on the application of a novel electric field-ionization setup for high-resolution laser spectroscopy measurements on bunched fast atomic beams in a collinear geometry. In combination with multi-step resonant excitation to Rydberg states using pulsed lasers, the field ionization technique demonstrates increased sensitivity for isotope separation and measurement of atomic parameters over previous non-resonant laser ionization methods. The setup was tested at the Collinear Resonance Ionization Spectroscopy experiment at ISOLDE-CERN to perform high-resolution measurements of transitions in the indium atom from the text {5s}^2text {5d},^2text {D}_{5/2} and text {5s}^2text {5d},^2text {D}_{3/2} states to text {5s}^2np ^2P and text {5s}^2ntext {f},^2F Rydberg states, up to a principal quantum number of n=72. The extracted Rydberg level energies were used to re-evaluate the ionization potential of the indium atom to be 46,670.107(4),hbox {cm}^{-1}. The nuclear magnetic dipole and nuclear electric quadrupole hyperfine structure constants and level isotope shifts of the text {5s}^2text {5d},^2text {D}_{5/2} and text {5s}^2text {5d},^2text {D}_{3/2} states were determined for ^{113,115}In. The results are compared to calculations using relativistic coupled-cluster theory. A good agreement is found with the ionization potential and isotope shifts, while disagreement of hyperfine structure constants indicates an increased importance of electron correlations in these excited atomic states. With the aim of further increasing the detection sensitivity for measurements on exotic isotopes, a systematic study of the field-ionization arrangement implemented in the work was performed at the same time and an improved design was simulated and is presented. The improved design offers increased background suppression independent of the distance from field ionization to ion detection.

Advantage of multi-step vibrational excitation in laser assisted aerodynamic separation of sulfur isotopes and a novel method of estimating the separation efficiency of the process

The advantage of a red-shifted laser source in furthering the obtainable enrichment factor by laser assisted aerodynamic separation process has been reported. The enhancement owes its origin to the efficient multi-photon excitation possible here due to the red-shifted nature of the incident radiation. This has been experimentally validated in sulfur wherein the emission of a line tunable CW-CO2 laser interacted with SF6-Ar binary jet. Anharmonic splitting of the vibrational levels coupled with Coriolis rotational splitting facilitates such multi-photon up-pumping. Further, a novel spectroscopic method for estimation of relative concentration of isotopes following the above route is reported for the first time. The method exploits the resonant nature of the absorption on 10P(36) and 10P(20) lines of the CO2 laser by 34SF6 and 32SF6 isotopomers respectively. This method renders knowledge of absorption cross-sections irrelevant and facilitates precise measurement of separation factor. The details of the methodology are discussed in appendix section.

A Unified Approach for the Identification of Wiener, Hammerstein, and Wiener–Hammerstein Models by Using WH-EA and Multistep Signals

Wiener, Hammerstein, and Wiener–Hammerstein structures are useful for modelling dynamic systems that exhibit a static type nonlinearity. Many methods to identify these systems can be found in the literature; however, choosing a method requires prior knowledge about the location of the static nonlinearity. In addition, existing methods are rigid and exclusive for a single structure. This paper presents a unified approach for the identification of Wiener, Hammerstein, and Wiener–Hammerstein models. This approach is based on the use of multistep excitation signals and WH-EA (an evolutionary algorithm for Wiener–Hammerstein system identification). The use of multistep signals will take advantage of certain properties of the algorithm, allowing it to be used as it is to identify the three types of structures without the need for the user to know a priori the process structure. In addition, since not all processes can be excited with Gaussian signals, the best linear approximation (BLA) will not be required. Performance of the proposed method is analysed using three numerical simulation examples and a real thermal process. Results show that the proposed approach is useful for identifying Wiener, Hammerstein, and Wiener–Hammerstein models, without requiring prior information on the type of structure to be identified.

Evolution of Octupole Deformation in Radium Nuclei from Coulomb Excitation of Radioactive Ra222 and Ra228 Beams

There is sparse direct experimental evidence that atomic nuclei can exhibit stable "pear" shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in ^{222,228}Ra nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing ^{222}Ra as pear shaped with stable octupole deformation, while ^{228}Ra behaves like an octupole vibrator.

Photocatalytic removal of airborne indoor pollutants by IR illuminated silver coated TiO2 catalyst: Advantage of one-dimensional TiO2 nanostructures in IR active photocatalysis

The development of IR sensitive photocatalysts is indispensable for the abatement of indoor pollutants as most of the photocatalysts mainly absorb radiation in the UV region and weakly in the visible region and not responding to indoor conditions. On the other hand, IR photons initiated photochemical reaction needs a highly efficient excited charge separation step as it is a multi-excitation process. In order to enhance the charge separation process in multi-step excitation photocatalytic systems, in this investigation the photocatalytic activities of silver coated 1-D TiO2 nanotubes were employed and the photocatalytic activity of 1-D TiO2nanotubes was compared with the photocatalytic activity of TiO2 nanoparticles. A superior photocatalytic activity was noted with the silver coated 1-D TiO2 nanotubes under IR irradiations than that of silver coated TiO2 nanoparticles. The impedance measurements were conducted by electrochemical impedance spectroscopy to differentiate the transport resistances, electron-hole recombination and electron lifetime of the silver coated 1-D TiO2nanotubes and nanoparticles. The possibility of the use of silver coated 1-D TiO2 nanotubes for the degradation of common airborne pollutants with near IR photons (similar to indoor conditions) was successfully demonstrated.

Evidence for Rigid Triaxial Deformation in Ge76 from a Model-Independent Analysis

An extensive, model-independent analysis of the nature of triaxial deformation in ^{76}Ge, a candidate for neutrinoless double-beta (0νββ) decay, was carried out following multistep Coulomb excitation. Shape parameters deduced on the basis of a rotational-invariant sum-rule analysis provided considerable insight into the underlying collectivity of the ground-state and γ bands. Both sequences were determined to be characterized by the same β and γ deformation parameter values. In addition, compelling evidence for low-spin, rigid triaxial deformation in ^{76}Ge was obtained for the first time from the analysis of the statistical fluctuations of the quadrupole asymmetry deduced from the measured E2 matrix elements. These newly determined shape parameters are important input and constraints for calculations aimed at providing, with suitable accuracy, the nuclear matrix elements relevant to 0νββ.

Dirac Phenomenological Analyses of 1.047-GeV Proton Inelastic Scatterings from 62Ni and 64Ni

Unpolarized 1.047 GeV proton inelastic scatterings from Ni isotopes, $^{62}$Ni and $^{64}$Ni are analyzed phenomenologically employing an optical potential model and the first order collective model in the relativistic Dirac coupled channel formalism. The Dirac equations are reduced to the Schr\"{o}dinger-like second-order differential equations and the effective central and spin-orbit optical potentials are analyzed by considering mass number dependence. The multistep excitation via $2^+$ state is found to be important for the $4^+$ state excitation in the ground state rotational band at the proton inelastic scatterings from the Ni isotopes. The calculated deformation parameters for the 2$^+$, the 4$^+$ states of the ground state rotational band and the first 3$^-$ state are found to agree pretty well with those obtained in the nonrelativistic calculations.

A fast multi-step prediction and rolling optimization excitation control method for multi-machine power system

A fast multi-step prediction and rolling optimization excitation control method for multi-machine power system

Optical characterization of one-step synthesis of ternary nanoalloy by laser ablation of stainless steel target in Hexane

In this work, we ablated stainless steel target in Hexane by 355nm by tuning laser power to synthesize ternary nanoalloys from its constituents. XRD patterns didn't match with any machine code of carbides, carbonyls and oxides of target elements. Also, they didn't match with any of binary alloys, suggesting the formation of carbides or carbonyls of ternary nanoalloys. In addition, the optical properties of nanoalloys confirms the resonance fluorescence and multistep excitation. By tuning laser power, the shape of nanoalloys is controlled.

First measurement with a new setup for low-energy Coulomb excitation studies at INFN LNL

A new segmented particle detector, SPIDER, has been designed to be used as an ancillary device with the GALILEO γ-ray spectrometer, as well as with other multi-detector γ-ray arrays that will be available at LNL in the future (e.g. AGATA). To commission the SPIDER-GALILEO experimental setup, a multi-step Coulomb excitation experiment was carried out with a 240 MeV beam of 66Zn produced by the Tandem-XTU accelerator at INFN Laboratori Nazionali di Legnaro. The measured particle and γ-ray spectra are compared with the results of detailed GEANT4 simulations which used the Coulomb excitation cross sections, estimated with the computer code GOSIA, as an input. The preliminary results indicate that precise transition probabilities will be obtained which are essential for solving discrepancies reported in the literature for this nucleus.

Quantum control and enhancement of multi-color emissions in upconversion nanoparticles

Upconversion luminescence (UCL) of lanthanide-doped nanomaterials is usually a low-efficiency nonlinear process, involving multi-step, multi-channel transitions in a multi-level system. Here, we demonstrate quantum control and enhancement of multi-color (e.g., red and green) UCLs of NaYF4:Yb3+/Er3+ nanoparticles with metallic Fabry-Perot micro-cavities. Besides realization of controlled single-color UCLs, their internal quantum efficiencies are strongly enhanced, up to 3–4 orders of times. Experimental results indicate that the controlled single-color UCLs and enhancements are caused not only by modifications of the spontaneous radiation rates for the red- and green-color transitions but also by influencing the intermediate transitions to result in modified distributions of electrons in each of the multiple Er3+ levels, facilitating emission of either red- or green-color light. This work suggests a way to control photon emissions in systems with multi-channel transitions and/or multi-step excitations.