Cross-section Spectra Research Articles

A Divide-and-Conquer Strategy for Quantification of Light Absorption, Scattering, and Emission Properties of Fluorescent Nanomaterials in Solutions.

Optical properties of fluorescent materials including their UV-vis absorption, scattering, and on-resonance fluorescence activities are strongly wavelength-dependent. Reported herein is a divide-and-conquer strategy for experimental quantification of fundamental optical constants of fluorescent nanomaterials including their UV-vis absorption, scattering, and on-resonance-fluorescence (ORF) cross-section spectra and ORF fluorescence and light scattering depolarization spectra. The fluorophore UV-vis extinction spectrum is first divided into a blue and a red wavelength region. The UV-vis extinction cross-section spectrum in the blue wavelength region is decomposed into its absorption and scattering extinction spectra straightforwardly using the established polarized resonance synchronous spectroscopic technique. In its red wavelength region, however, the fluorophores can be simultaneous photon absorbers, scatterers, and anti-Stokes-shifted, on-resonance, and Stokes-shifted fluorescence emitters under the resonance excitation and detection conditions. A polarized anti-Stokes'-shifted, on-resonance, and Stokes'-shifted spectroscopic method is developed for quantifying fluorophore absorption, scattering, one-resonance fluorescence (ORF) cross-section spectra, and scattering and ORF fluorescence depolarization spectra in this wavelength region. Example applications of the presented techniques were demonstrated with fluorescent polystyrene nanoparticles, fluorescent quantum dots, and molecular fluorophores Rhodamine 6G and Eosin Y.

Tunable dual-wavelength laser based on Nd:YVO4/Nd:GdVO4 combined crystal.

A tunable dual-wavelength laser (DWL) based on Nd:YVO4/Nd:GdVO4 combined crystal is presented. The frequency separation tuning characteristics of the DWL are investigated experimentally. In the experiments, the DWL with tunable frequency separation is obtained with fixed pumping power and controlled heat sink temperature (Tc) of the combined crystal. The frequency separations are measured at 351.11-316.15 GHz by varying Tc from 5.0 °C to 40.0 °C, with a slope of -0.95 GHz/°C. When Tc is kept at 32.3 °C, a 435-mW power-balanced DWL signal is achieved with frequency separation at 324.29 GHz. By analyzing the experimental results from the perspective of thermal-induced emission cross section (ECS) spectra evolution of the combined crystal, it is found the frequency separation tuning of the DWL is caused by the different ECS spectral wavelength shifting rates of the Nd:YVO4 and Nd:GdVO4 crystals with Tc varying. The analysis results are in good agreement with the experimental results.

GPU-Accelerated Computation of Time-Evolving Electromagnetic Backscattering Field From Large Dynamic Sea Surfaces

An efficient facet-based composite scattering model (FBCSM) is developed for calculating the time-evolving electromagnetic (EM) scattering field (TESF) to study the normalized radar cross section and Doppler spectrum characteristics from dynamic sea surfaces. The dynamic sea surface comprises two-scale profiles: small-scale capillary ripples modulated by large-scale gravity waves, which are modeled by millions of small facets. In microwave bands, two scattering mechanisms, quasi-specular scattering with respect to gravity waves and Bragg scattering with respect to ripples, are taken into account in the FBCSM for computation of the time-evolving EM scattering field under diverse polarizations. However, it may be very time-consuming and difficult to calculate the TESF due to the high resolution and dynamic complexity of the large dynamic sea surface. In this paper, the NVIDIA Tesla K80 graphics processing unit (GPU) with the compute unified device architecture is utilized to improve the computational performance of the TESF. The whole GPU-based TESF computation includes the optimal use of temporary variables, shared memory, constant memory and register, fast-math compiler options, asynchronous data transfer, and the most suitable block size and number of registers. By utilizing the proposed five improvement strategies, a significant speedup of $1200 \times $ can be achieved for computation of TESF from large dynamic sea surfaces for microwave bands compared with the single-threaded C program executed on the Intel(R) Core(TM) i5-3450 CPU.

Anisotropic stimulated emission cross-section measurement in Nd:YVO4

As a crucial parameter in the design and analysis of laser performances, stimulated emission (SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention. In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition in Nd:YVO4 are measured in different propagating directions. Based on Fuchtbauer–Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO4 are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.

Er,Yb:Ca3RE2(BO3)4 (RE=Y, Gd) – Novel 1.5 μm Laser Crystals

The search for new crystalline host materials for the usage in lasers emitting in the eye-safe spectral range of 1.5–1.6 µm is an important task. The aim of this work was to study the growth technique, spectroscopic properties and laser characteristics of new active media – crystals Er3+,Yb3+:Ca2RE2(BO3)4(RE=Y, Gd).Calcium-yttrium Er3+,Yb3+:Ca3Y2(BO3)4(CYB) and calcium-gadolinium Er3+,Yb3+: Ca2Gd2(BO3)4 (CGB) oxoborate crystals co-doped with erbium and ytterbium ions were investigated. Polarized absorption and emission cross-section spectra were determined. The lifetimes of4I11/2and4I13/2energy levels of Er3+ions were measured and ytterbium-erbium energy transfer efficiencies were estimated. The calculation of the gain cross-section spectra was performed. By using of Er3+,Yb3+: Ca2RE2(BO3)4 (RE=Y, Gd) crystals the laser performance was realized, for the first time to the best of our knowledge. The laser characteristics were studied in a quasi-CW (QCW) laser operation.The wide band with a peak at the wavelength of 976 nm is observed in the absorption spectra of both crystals. This peak coincides with the emission wavelength of the pump laser diodes for Yb-doped active media. The maximum value of absorption cross-section was 1.7 × 10–20cm2for polarizationE//bfor both crystals. The lifetimes of the upper laser level4I13/2of Er3+ions were 580 ± 30 μs and 550 ± 30 μs for Er,Yb:CYB and Er,Yb:CGB crystals, respectively. The energy transfer efficiencies from ytterbium to erbium ions for an Er,Yb:CYB and Er,Yb:CGB crystals were 94 % and 96 %, respectively. According to gain spectrum of the Er,Yb:CYB crystal the gain band peak is centered at the wavelength of 1530 nm. The maximum QCW output power was 0.5 W with slope efficiency of 13 % regarding to absorbed pump power for an Er,Yb: CYB crystal. The laser beam parameter M2did not exceed < 1.5.Based on the obtained results, it can be concluded that these crystals are promising active media for lasers emitting in the spectral range of 1.5–1.6 μm for the usage in laser rangefinder and laser-induced breakdown spectroscopy systems, and LIDARs.

Cross section spectral distribution of Er3+ electronic transitions in SrGdGa3O7 single-crystal

Abstract Visible and infrared absorption and emission spectra of Er3+-doped strontium gadolinium gallate (SrGdGa3O7) single-crystal were measured at room temperature. From the measured fluorescence spectra, the Er3+ emission cross section spectra were calculated at first. Then, by utilizing McCumber relation, the absorption cross section spectra were further calculated. In parallel, the absorption cross section spectra were also calculated from the measured absorption spectra of the crystal, and compared with those spectra calculated from the McCumber relation. The comparison shows that the absorption cross section spectra obtained using the McCumber relation are in reasonable agreement with those deduced from the measured absorption spectrum.

Correction to "Quantification of Material Fluorescence and Light Scattering Cross Sections Using Ratiometric Bandwidth-Varied Polarized Resonance Synchronous Spectroscopy".

Presented herein is the ratiometric bandwidth-varied polarized resonance synchronous spectroscopy (BVPRS2) method for quantification of material optical activity spectra. These include the sample light absorption and scattering cross-section spectrum, the scattering depolarization spectrum, and the fluorescence emission cross-section and depolarization spectrum in the wavelength region where the sample both absorbs and emits. This ratiometric BVPRS2 spectroscopic method is a self-contained technique capable of quantitatively decoupling material fluorescence and light scattering signal contribution to its ratiometric BVPRS2 spectra through the linear curve-fitting of the ratiometric BVPRS2 signal as a function of the wavelength bandwidth used in the PRS2 measurements. Example applications of this new spectroscopic method are demonstrated with materials that can be approximated as pure scatterers, simultaneous photon absorbers/emitters, simultaneous photon absorbers/scatterers, and finally simultaneous phot...

Bound states in the continuum and Fano resonances in the strong mode coupling regime

The study of resonant dielectric nanostructures with high refractive index is a new research direction in nanoscale optics and metamaterial-inspired nanophotonics. Because of the unique optically-induced electric and magnetic Mie resonances, high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications. Here we study strong coupling between modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator's aspect ratio varies. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich-Wintgen scenario of destructive interference. We explain the physics of these states in terms of multipole decomposition and show that their appearance is accompanied by drastic change of the far-field radiation pattern. We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra. Our theoretical findings are confirmed by microwave experiments for the scattering of a high-index cylindrical resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high quality factor helps to extend substantially functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices.

Effect of scanning speeds on electrochemical corrosion resistance of laser cladding TC4 alloy**Project supported by the National Natural Science Foundation of China (Grant Nos. 61475117 and 51471084), the National Key Research and Development Program of China (Grant No. 2017YFB1103604), and the Tianjin Municipal Special Program of Talents Development for Excellent Youth Scholars, China (Grant No. TJTZJHQNBJRC-2-15).

In order to study the effect of scanning speed on the electrochemical corrosion resistance of laser cladding TC4 alloy in artificial seawater, the x-ray diffraction analysis, microstructure of cross-section, microhardness variation, and impedance spectrum have been studied in comparison with the TC4 titanium alloy. The results show that the main phase of cladding coating is α-Ti, and the change of scanning speed has no obvious effect on it; therefore, the supersaturated α-Ti solid solution is formed, and the acicular martensite is obtained. As the scanning speed increases, the microstructure of cladding coating is orthogonal basket-weave, the crystal surface spacing decreases, and the average microhardness of laser cladding TC4 alloy slightly increases. When the scanning speed increases to 10 mm/s, the microhardness is about 14.71% higher than that of the substrate, and the electrochemical corrosion resistance of laser cladding TC4 alloy is also improved, which is about 2.48 times more than the substrate. Grain refinement has a great effect on enhancing the anti-electrochemical corrosion.

Factor analysis of inelastic electron scattering cross section spectra of FeSi2

Iron disilicide is widely used in creation of such nanotechnology devices as photoelectric converters. The investigation of iron silicide FeSi2 with the method of inelastic electron scattering cross-section spectroscopy was carried out. The decomposition of inelastic electron scattering cross-section spectra of FeSi2 to bulk and surface energy loss components using factor analysis was carried out. The amplitude of energy loss components can be used for identification of their origin.

Orbital angular momentum dichroism in nanoantennas

When light interacts with matter, dichroism with respect to the handedness of circularly polarized light is well established. But what happens if the light further possesses an orbital angular momentum? In this paper, we discuss possible definitions of orbital angular momentum dichroism and define a new type of dichroism, the class dichroism. By numerically calculating the scattering cross-section spectra, we study the dichroism of a plasmonic nanostructure interacting with orbital angular momentum light. By considering the exemplary case of twisted, stacked nanorods, we show that the orbital angular momentum dichroism can be as strong as dichroism induced by circular polarization. We present a detailed classification of the different types of orbital angular momentum dichroism, which paves the way for new chiroptic spectroscopic techniques.

Characterization of core–shell nanostructure consisting Si–Au–SiO2 based on manipulation of optical properties

In this article, we investigated some physical characteristics of core–shell nanostructure in optical regime and perturbation has been also introduced as an effective method in shaping of optical properties. The proposed nanostructures are composed of the selected materials as: Silicon, Silicon Dioxide and Gold. At first, the extinction cross section spectra are calculated for multilayer core–shell nanostructures in optical range and the configuration effect of the constructed materials in a multilayer nanostructure are investigated for determination of Plasmon range. Then, the new structures of core–shell nanoparticles (gold–silicon) are presented, which have an amount of impurity particle in their shells as perturbation and also their extinction cross section spectra are calculated. The obtained results in this article give a proper approach about perturbation effect in broadening, sharpening and shifting of optical response which are decisive factors especially nano-network systems. Indeed, it has been proposed that the impurity particles in the shells can be a mechanism for tuning of optical characteristics of the presented nanoparticles in practical fields and also creation of local oscillations as plasmonic resonances in a considered optical range. Besides, redshift in extinction cross section can be also created by particle perturbation. At the end, the effective permittivity of the perturbed core-shells are extracted. The optional frequency range is selected between 300 and 900 (THz).

Cooper minimum in singly ionized and neutral argon

We present an analysis of the appearance of the Cooper Minimum in singly ionized argon in both the photoionization cross-section (PICS) and high-harmonic generation (HHG) spectrum. We employ two computational approaches based on the same R-matrix technique to provide a coherent description of the atomic structure of the Ar+ system, finding that the PICS and HHG spectrum are affected differently by the inclusion of additional residual ion states and the improved description of correlation effects. Both the PICS and HHG spectrum possess a clear minimum for all atomic structure models used, with the centre of the minimum at 55 eV in the PICS and 60 eV in the HHG spectrum for the most complete description employed. The HHG minimum is systematically shifted to higher energies with respect to the PICS minimum. We also find that the initial magnetic alignment (magnetic quantum number) of the Ar+ system does not affect substantially the position and shape of the HHG minimum (given a sufficiently detailed atomic structure description), but the harmonic yield is enhanced by two-orders of magnitude for M_L = 1 over M_L = 0. We also perform similar calculations for neutral argon, finding that this system is more sensitive to enhancements in the atomic structure description.

Method for estimating the Stark splitting of rare-earth ions from the measured cross-section spectra.

A method to estimate the Stark levels of the rare-earth ions doped in a laser medium from the measured emission and absorption cross-sections is proposed. The method is based on the McCumber theory, which can calculate the emission/absorption cross-sections from the given Stark levels. By fitting the calculated emission/absorption spectra to the measured ones through a numerical optimization process, the Stark levels of the RE ions can be determined. As examples, the Stark levels of the laser-emission-related manifolds of Er3+ and Yb3+ ions in a gain fiber and two doped glasses have been determined by the proposed method. The data were then used to analyze the temperature-dependent population of the Stark levels. This method avoids the difficulties in direct measurement of the Stark levels in a cryogenic temperature environment. It is important to the evaluation of the thermal load, distribution, and design of the thermal management system of high-power fiber lasers and amplifiers.

Coupled Cluster and Time-Dependent Density Functional Theory Description of Inner Shell Photoabsorption Cross Sections of Molecules.

Near K-edge photoabsorption cross section spectra of a number of molecules, namely, water, ammonia, acetone, acetaldehyde, furan, and pyrrole, were obtained at the nitrogen, oxygen, and carbon K-edges with the Coupled Cluster ansatz (CC) and with the Time-Dependent Density Functional Theory (TDDFT) by treating the inner shell excitations as individual channels, separated from the valence part of the spectrum. The discretized electronic pseudospectrum, obtained with quadratically integrable basis sets ( a.k.a. L2) at the CC or TDDFT level, is used to reconstruct the complex dipole polarizability function, from which the photoabsorption cross section near the K-edge is obtained by a continued fraction based analytic continuation procedure. The CC2 and CCSD results are in good agreement with experimental data, while the TDDFT results yield reliable cross sections. Overall, the results obtained in this work indicate that our method can be used for the treatment of the NEXAFS spectra, with the advantage that the electronic excitations in the K-edges can be easily obtained at low computational cost using TDDFT.

Numerical design of Au/Si core-shell nanoparticles

Resonant metal-dielectric nanostructures of the core-shell type can provide unusual optical properties originated from spectral overlapping of electric and magnetic resonances of the nanostructure components. Here we numerically investigate the geometry and scattering cross section spectra of a core-shell nanostructure, where the core is gold, and the shell is crystalline silicon. We study spherical and cylindrical types of the nanostructures and search optimal geometrical parameters in the terms of spectral overlapping of the resonances. The obtained geometry parameters can be utilized for the first experimental realization of the metal-dielectric core-shell nanostructures.

Validity of the McCumber Theory at High Temperatures in Erbium and Ytterbium-Doped Aluminosilicate Fibers

The temperature dependence of the emission and absorption cross sections of Er and Yb ions in rare-earth-doped aluminosilicate optical fibers is experimentally investigated. The obtained results demonstrate that the McCumber theory accurately predicts the temperature-induced changes of the emission cross section spectrum up to 500 °C when the absorption spectra measured at the considered temperature is used for the calculations instead of the one acquired at ambient temperature. Finally, we also demonstrate that the various heating steps up to 500 °C are not affecting the fiber guiding properties and no permanent effect is observed on the emission and absorption cross section spectra measured at room temperature.

Crystal growth, spectroscopy and first laser operation of a novel disordered tetragonal Tm:Na2La4(WO4)7 tungstate crystal

Tm3+:Na2La4(WO4)7, a disordered tetragonal scheelite-type tungstate crystal, is grown by the Czochralski method. The polarized absorption, stimulated-emission and gain cross-section spectra are determined. The maximum σSE is 1.62 × 10–20 cm2 at 1788.6 nm for σ-polarization. The Judd-Ofelt parameters for Tm3+ are Ω2 = 10.321, Ω4 = 0.183 and Ω6 = 2.122 [10–20 cm2]. The radiative lifetime of the 3F4 state is 1.63 ms. Raman spectroscopy reveals a maximum phonon energy of 923 cm−1. Laser operation under diode-pumping is achieved with both a-cut and c-cut Tm:Na2La4(WO4)7 crystals, reaching a maximum output power for the a-cut of 715 mW at ~ 1937 nm with a slope efficiency of 34%. Microchip laser operation using the c-cut crystal yields a slope efficiency of 41%. The Tm:Na2La4(WO4)7 crystal is promising for mode-locked lasers due to its broadband emission.

Quantification of Material Fluorescence and Light Scattering Cross Sections Using Ratiometric Bandwidth-Varied Polarized Resonance Synchronous Spectroscopy.

Presented herein is the ratiometric bandwidth-varied polarized resonance synchronous spectroscopy (BVPRS2) method for quantification of material optical activity spectra. These include the sample light absorption and scattering cross-section spectrum, the scattering depolarization spectrum, and the fluorescence emission cross-section and depolarization spectrum in the wavelength region where the sample both absorbs and emits. This ratiometric BVPRS2 spectroscopic method is a self-contained technique capable of quantitatively decoupling material fluorescence and light scattering signal contribution to its ratiometric BVPRS2 spectra through the linear curve-fitting of the ratiometric BVPRS2 signal as a function of the wavelength bandwidth used in the PRS2 measurements. Example applications of this new spectroscopic method are demonstrated with materials that can be approximated as pure scatterers, simultaneous photon absorbers/emitters, simultaneous photon absorbers/scatterers, and finally simultaneous photon absorbers/scatterers/emitters. Because the only instruments needed for this ratiometric BVPRS2 technique are the conventional UV-vis spectrophotometer and spectrofluorometer, this work should open doors for routine decomposition of material UV-vis extinction spectrum into its absorption and scattering component spectra. The methodology and insights provided in this work should be of broad significance to all chemical research that involves photon/matter interactions.

First-principles spectra of Au nanoparticles: from quantum to classical absorption

ABSTRACTAbsorption cross-section spectra for gold nanoparticles were calculated using fully quantum Stochastic Density Functional Theory and a classical Finite-Difference Time Domain Maxwell solver. Spectral shifts were monitored as a function of size (1.3–) and shape (octahedron, cubeoctahedron and truncated cube). Even though the classical approach is forced to fit the quantum time-dependent density functional theory at , at smaller sizes there is a significant deviation as the classical theory is unable to account for peak splitting and spectral blueshifts even after quantum spectral corrections. We attribute the failure of classical methods at predicting these features to quantum effects and low density of states in small nanoparticles. Classically, plasmon resonances are modelled as collective conduction electron excitations, but at small nanoparticle size these excitations transition to few or even individual conductive electron excitations, as indicated by our results.