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Showing papers on "Doppler broadening published in 2021"


Journal ArticleDOI
TL;DR: In this article, the first order helical Laguerre-Gaussian mode (also called donut mode) is used to improve the energy throughput of nonlinear spectral broadening in gas-filled multipass cells.
Abstract: The first-order helical Laguerre–Gaussian mode (also called donut mode) is used to improve the energy throughput of nonlinear spectral broadening in gas-filled multipass cells. The method proposed in this Letter enables, for the first time to the best of our knowledge, the nonlinear spectral broadening of pulses with energies beyond 100 mJ and is suitable for an average power of more than 500 W while conserving an excellent spatio-spectral homogeneity of ∼98% and a Gaussian-like focus profile. Additionally compressibility from 1.3 ps to 37 fs is demonstrated.

50 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed analysis for the influence of waveguide geometry and GO film thickness on the propagation loss, nonlinear parameter, and nonlinear figure of merit (FOM) is performed.
Abstract: The Kerr nonlinear optical performance of silicon nanowire waveguides integrated with 2D layered graphene oxide (GO) films is theoretically studied and optimized based on experimentally measured linear and nonlinear optical parameters of the GO films. The strong mode overlap between the silicon nanowires and highly nonlinear GO films yields a significantly enhanced Kerr nonlinearity for the hybrid waveguides. A detailed analysis for the influence of waveguide geometry and GO film thickness on the propagation loss, nonlinear parameter, and nonlinear figure of merit (FOM) is performed. The results show that the effective nonlinear parameter and nonlinear FOM can be increased by up to ∼52 and ∼79 times relative to bare silicon nanowires, respectively. Self-phase modulation (SPM)-induced spectral broadening of optical pulses is used as a benchmark to evaluate the nonlinear performance, examining the trade-off between enhancing Kerr nonlinearity and minimizing loss. By optimizing the device parameters to balance this, a high spectral broadening factor of 27.8 can be achieved – more than 6 times that achieved in previous experiments. Finally, the influence of pulse chirp, material anisotropy, and the interplay between saturable absorption and SPM is also discussed, together with the comparison between the spectral broadening after going through GO-coated and graphene-coated silicon waveguides. These results provide useful guidance for optimizing the Kerr nonlinear optical performance of silicon waveguides integrated with 2D layered GO films.

32 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a one-photon optical spectroscopy free of first-order Doppler and transit broadening, which can also be obtained with more easily prepared ensembles of ions, if performed with midinfrared radiation.
Abstract: Optical spectroscopy in the gas phase is a key tool to elucidate the structure of atoms and molecules and of their interaction with external fields. The line resolution is usually limited by a combination of first-order Doppler broadening due to particle thermal motion and of a short transit time through the excitation beam. For trapped particles, suitable laser cooling techniques can lead to strong confinement (Lamb-Dicke regime, LDR) and thus to optical spectroscopy free of these effects. For non-laser coolable spectroscopy ions, this has so far only been achieved when trapping one or two atomic ions, together with a single laser-coolable atomic ion [1,2]. Here we show that one-photon optical spectroscopy free of Doppler and transit broadening can also be obtained with more easily prepared ensembles of ions, if performed with mid-infrared radiation. We demonstrate the method on molecular ions. We trap approximately 100 molecular hydrogen ions (HD$^{+}$) within a Coulomb cluster of a few thousand laser-cooled atomic ions and perform laser spectroscopy of the fundamental vibrational transition. Transition frequencies were determined with lowest uncertainty of 3.3$\times$10$^{-12}$ fractionally. As an application, we determine the proton-electron mass ratio by matching a precise ab initio calculation with the measured vibrational frequency.

29 citations


Journal ArticleDOI
TL;DR: In this article, the authors evaluate various sources of errors that occur when attempting to produce a specified coherent change of a two-state quantum system using six popular coherent control techniques: resonant excitation, adiabatic following, composite adiabel passage, universal composite pulses, shortcut to adiability, and single-shot shaped pulses.
Abstract: We evaluate various sources of errors that occur when attempting to produce a specified coherent change of a two-state quantum system using six popular coherent control techniques: resonant excitation, adiabatic following, composite adiabatic passage, universal composite pulses, shortcut to adiabaticity, and single-shot shaped pulses. As error sources, we consider spatial intensity distribution, transit time variation, inhomogeneous broadening, Doppler broadening, unwanted chirp, and shape errors, as well as errors generated by counter-rotating terms. For the various error types, different techniques emerge as the best performers, but overall we find that universal composite pulses perform most consistently and are most resilient to errors compared to all other procedures.

19 citations


Journal ArticleDOI
TL;DR: Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump-probe experiments.
Abstract: This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas-filled multi-pass cell to generate sub-100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 µJ, respectively, for pump–probe experiments at the free-electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump–probe experiments.

17 citations


Journal ArticleDOI
TL;DR: In this paper, temperature tunable spectral broadening using a nonlinear ultra-silicon-rich nitride device consisting of a 3mmlong cladding-modulated Bragg grating and a 7mm-long nonlinear channel waveguide was demonstrated.
Abstract: Spectral tunability methods used in optical communications and signal processing leveraging optical, electrical, and acousto-optic effects typically involve spectral truncation that results in energy loss Here we demonstrate temperature tunable spectral broadening using a nonlinear ultra-silicon-rich nitride device consisting of a 3-mm-long cladding-modulated Bragg grating and a 7-mm-long nonlinear channel waveguide By operating at frequencies close to the grating band edge, in an apodized Bragg grating, we access strong grating-induced dispersion while maintaining low losses and high transmissivity We further exploit the redshift in the Bragg grating stopband due to the thermo-optic effect to achieve tunable dispersion, leading to varying degrees of soliton-effect compression and self-phase-modulation-induced spectral broadening We observe an increase in the bandwidth of the output pulse spectrum from 69 to 106 nm as temperature decreases from 70°C to 25°C, in good agreement with simulated results using the generalized nonlinear Schrodinger equation The demonstrated approach provides a new avenue to achieve on-chip laser spectral tuning without loss in pulse energy

16 citations


Journal ArticleDOI
TL;DR: In this paper, a high spatial resolution coherent Doppler wind lidar (CDWL) incorporating the differential correlation pair (DCP) technique is proposed and demonstrated, and the performance of the new method is validated in the comparison experiment with the CDWLs adopting conventional schemes.
Abstract: A high spatial resolution coherent Doppler wind lidar (CDWL) incorporating the differential correlation pair (DCP) technique is proposed and demonstrated. By employing pulse pair with appropriate window functions, the spatial resolution can be enhanced, as the common parts of the correlation pair can be eliminated in the differential data processing. The performance of the new method is validated in the comparison experiment with the CDWLs adopting conventional schemes. Under a given peak power, the DCP technique provides higher wind velocity accuracy compared with a conventional pulsed CDWL where the laser spectral broadening caused by short pulses can be avoided and the carrier-to-noise ratio is improved. At a laser peak power of 250 W, with a spatial and temporal resolution of 3.3 m and 1 s, continuous radial wind profiling over 700 m is realized with a maximum error of 0.1 m/s.

15 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of varying plasma generation conditions (nanosecond versus femtosecond laser ablation) and ambient environments (argon versus helium gas) on spectral features generated from Zircaloy-4 targets with varying hydrogen isotopic compositions were studied.
Abstract: Laser-induced breakdown spectroscopy is a promising method for rapidly measuring hydrogen and its isotopes, critical to a wide range of disciplines (e.g. nuclear energy, hydrogen storage). However, line broadening can hinder the ability to detect finely spaced isotopic shifts. Here, the effects of varying plasma generation conditions (nanosecond versus femtosecond laser ablation) and ambient environments (argon versus helium gas) on spectral features generated from Zircaloy-4 targets with varying hydrogen isotopic compositions were studied. Time-resolved 2D spectral imaging was employed to detail the spatial distribution of species throughout plasma evolution. Results highlight that hydrogen and deuterium isotopic shifts can be measured with minimal spectral broadening in a ∼ 10 Torr helium gas environment using ultrafast laser-produced plasmas.

14 citations


Journal ArticleDOI
TL;DR: In this article, a detailed analysis for the influence of waveguide geometry and GO film thickness on the propagation loss, nonlinear parameter, and nonlinear figure of merit (FOM) is performed.
Abstract: The Kerr nonlinear optical performance of silicon nanowire waveguides integrated with 2D layered graphene oxide (GO) films is theoretically studied and optimized based on experimentally measured linear and nonlinear optical parameters of the GO films. The strong mode overlap between the silicon nanowires and highly nonlinear GO films yields a significantly enhanced Kerr nonlinearity for the hybrid waveguides. A detailed analysis for the influence of waveguide geometry and GO film thickness on the propagation loss, nonlinear parameter, and nonlinear figure of merit (FOM) is performed. The results show that the effective nonlinear parameter and nonlinear FOM can be increased by up to 52 and 79 times relative to bare silicon nanowires, respectively. Self-phase modulation (SPM)-induced spectral broadening of optical pulses is used as a benchmark to evaluate the nonlinear performance, examining the tradeoff between enhancing Kerr nonlinearity and minimizing loss. By optimizing the device parameters to balance this, a high spectral broadening factor of 27.8 can be achieved, more than 6 times that achieved in previous experiments. Finally, the influence of pulse chirp, material anisotropy, and the interplay between saturable absorption and SPM is also discussed, together with the comparison between the spectral broadening after going through GO-coated and graphene-coated silicon waveguides. These results provide useful guidance for optimizing the Kerr nonlinear optical performance of silicon waveguides integrated with 2D layered GO films.

14 citations


Journal ArticleDOI
TL;DR: In this paper, a study of vacancies in Fex(CoCrMnNi)100-x medium and high-entropy alloys by positron annihilation spectroscopy (PAS) was carried out.

12 citations


Journal ArticleDOI
TL;DR: In this article, a positron annihilation study using state-of-the-art experimental and theoretical methods in n-type and semi-insulating β - Ga 2 O 3 was performed.
Abstract: We report a positron annihilation study using state-of-the-art experimental and theoretical methods in n-type and semi-insulating β - Ga 2 O 3. We utilize the recently discovered unusually strong Doppler broadening signal anisotropy of β - Ga 2 O 3 in orientation-dependent Doppler broadening measurements, complemented by temperature-dependent positron lifetime experiments and first principles calculations of positron–electron annihilation signals. We find that split Ga vacancies dominate the positron trapping in β - Ga 2 O 3 single crystals irrespective of the type of dopant or conductivity, implying concentrations of at least 1 × 1 0 18 c m − 3.

Journal ArticleDOI
TL;DR: In this paper, the authors used time and spectrally resolved pump-probe spectroscopy to investigate ultrafast exciton dynamics in bilayer 2D rhenium dichalcogenides.
Abstract: The optical and optoelectronic properties of two-dimensional (2D) semiconductors are dominated by excitons, which usually appear as well-defined peaks in the spectral domain. Thus, detailed behaviors of excitons can be understood by tracking transient changes of the fundamental spectral observables, i.e., the resonance energy and the spectral linewidth. Rhenium disulfide ($\mathrm{Re}{\mathrm{S}}_{2}$) is a 2D semiconductor that has recently attracted attention due to its excellent exciton properties, such as light-polarization selectivity and anisotropic coherent effects. However, an understanding of exciton dynamics and spectral behavior of excitons in $\mathrm{Re}{\mathrm{S}}_{2}$ is lacking. Here, we used time- and spectrally resolved pump-probe spectroscopy to investigate ultrafast exciton dynamics in bilayer $\mathrm{Re}{\mathrm{S}}_{2}$. Upon photoexcitation, the exciton resonance undergoes linewidth broadening and redshift, but they exhibit different dynamics, and an opposite pump fluence dependence on the approximately hundreds of picoseconds timescale. This is because the spectral broadening and the red-shift both have different origins (the exciton-carrier scattering and exciton-exciton attractive interaction, respectively) and different decay mechanisms (the trapping of carriers and exciton-exciton annihilation, respectively). On a longer timescale of \ensuremath{\sim}100 ps, both the spectral broadening and the redshift are well explained by the indirect recombination of carriers and lattice heating. This work provides in-depth insight into exciton dynamics in 2D rhenium dichalcogenides.

Journal ArticleDOI
TL;DR: In this article, the authors proposed to avoid ponderomotive broadening in harmonics by using the polarization gating technique, which is a well-known method to construct a laser pulse with temporally varying polarization.
Abstract: Nonlinear Compton scattering is a promising source of bright gamma rays. Using readily available intense laser pulses to scatter off the energetic electrons, on the one hand, allows us to significantly increase the total photon yield, but on the other hand, leads to a dramatic spectral broadening of the fundamental emission line as well as its harmonics due to the laser pulse shape induced ponderomotive effects. In this Letter we propose to avoid ponderomotive broadening in harmonics by using the polarization gating technique---a well-known method to construct a laser pulse with temporally varying polarization. We show that by restricting harmonic emission only to the region near the peak of the pulse, where the polarization is linear, it is possible to generate a bright narrow bandwidth comb in the gamma region.

Journal ArticleDOI
TL;DR: In this article, the authors presented an optical picture of linear-optics superradiance, based on a single scattering event embedded in a dispersive effective medium composed by the other atoms.
Abstract: We present an optical picture of linear-optics superradiance, based on a single scattering event embedded in a dispersive effective medium composed by the other atoms. This linear-dispersion theory is valid at low density and in the single-scattering regime, i.e., when the exciting field is largely detuned. The comparison with the coupled-dipole model shows a perfect agreement for the superradiant decay rate. Then we use two advantages of this approach. First we make a direct comparison with experimental data, without any free parameter, and show a good quantitative agreement. Second, we address the problem of moving atoms, which can be efficiently simulated by adding the Doppler broadening to the theory. In particular, we discuss how to recover superradiance at high temperature.

Journal ArticleDOI
TL;DR: The windowed multipole representation of nuclear cross sections has been proposed in this paper to generate Doppler broadening for low-energy nuclear cross-sections on-the-fly.
Abstract: Nuclear cross sections are basic inputs to any nuclear computation. Campaigns of experiments are fitted with the parametric $R$-matrix model of quantum nuclear interactions, and the resulting cross sections are documented---both pointwise and as resonance parameters (with uncertainties)---in standard evaluated nuclear data libraries (ENDF, JEFF, BROND, JENDL, CENDL, TENDL): these constitute our common knowledge of fundamental low-energy nuclear cross sections. In the past decade, a collaborative effort has been deployed to establish a new nuclear cross-section library format---the Windowed Multipole Library---with the goal of considerably reducing the computational cost of cross-section calculations in nuclear transport simulations. This paper lays the theoretical foundations underpinning these efforts. From general $R$-matrix scattering theory, we derive the windowed multipole representation of nuclear cross sections. Though physically and mathematically equivalent to $R$-matrix cross sections, the windowed multipole representation is particularly well suited for subsequent temperature treatment of angle-integrated cross sections, in particular Doppler broadening, which is the averaging of cross sections over the thermal motion of the target atoms. Doppler broadening is of critical importance in neutron transport applications, as it ensures the stability of many nuclear reactors (negative thermal reactivity). Yet, Doppler broadening of nuclear cross sections has been a considerable bottleneck for nuclear transport computations, often requiring memory-costly pretabulations. We show that the windowed multipole representation can perform accurate Doppler broadening analytically (up to the first reaction threshold), from which we derive cross-section temperature derivatives to any order---all computable on the fly (without precalculations stored in memory). Furthermore, we here establish a way of converting the $R$-matrix resonance parameters uncertainty (covariance matrices) into windowed multipole parameters uncertainty. We show that generating stochastic nuclear cross sections by sampling from the resulting windowed multipole covariance matrix can reproduce the cross-section uncertainty in the original nuclear data file. The windowed multipole representation is therefore a novel nuclear physics formalism able to generate Doppler broadened stochastic nuclear cross sections on the fly, unlocking breakthrough computational gains for nuclear computations. Through this foundational paper, we hope to make the windowed multipole representation accessible, reproducible, and usable for the nuclear physics community, as well as provide the theoretical basis for future research on expanding its capabilities.

Journal ArticleDOI
TL;DR: In this paper, a combination of emission and absorption spectroscopy with laser ablation and tuneable diode laser Absorption Spectroscopy (TDLAS) has been used to analyse laser-produced plasma of lithium.

Journal ArticleDOI
TL;DR: In this article, the formation of vacancy clusters and hydrogen-vacancy complexes with 30 keV H ion-irradiated pure titanium at different doses and temperatures was measured using Positron annihilation spectroscopy.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to quantify the measurement error due to self-absorption based on the calculation of the spectral radiance of a plasma in local thermodynamic equilibrium.

Journal ArticleDOI
TL;DR: In this article, the authors present experimental results which intentionally varied the mode 1 drive imbalance by up to 4% to test hydrodynamic predictions of flows and the resultant imploded core asymmetries and performance, as measured by a combination of DT neutron spectroscopy and high-resolution x-ray core imaging.
Abstract: Inertial confinement fusion implosions designed to have minimal fluid motion at peak compression often show significant linear flows in the laboratory, attributable per simulations to percent-level imbalances in the laser drive illumination symmetry. We present experimental results which intentionally varied the mode 1 drive imbalance by up to 4% to test hydrodynamic predictions of flows and the resultant imploded core asymmetries and performance, as measured by a combination of DT neutron spectroscopy and high-resolution x-ray core imaging. Neutron yields decrease by up to 50%, and anisotropic neutron Doppler broadening increases by 20%, in agreement with simulations. Furthermore, a tracer jet from the capsule fill-tube perturbation that is entrained by the hot-spot flow confirms the average flow speeds deduced from neutron spectroscopy.

Posted Content
TL;DR: In this paper, a hybridization of the multiplate continuum and the multi-pass cell spectral broadening techniques is proposed to compress 1.24 ps pulses to 39 fs by means of only a single spectral wideening stage, which neither requires vacuum parts nor custom-made optics.
Abstract: As Ultrafast laser technology advances towards ever higher peak and average powers, generating sub-50 fs pulses from laser architectures that exhibit best power-scaling capabilities remains a major challenge. Here, we present a very compact and highly robust method to compress 1.24 ps pulses to 39 fs by means of only a single spectral broadening stage which neither requires vacuum parts nor custom-made optics. Our approach is based on the hybridization of the multi-plate continuum and the multi-pass cell spectral broadening techniques. Their combination leads to significantly higher spectral broadening factors in bulk material than what has been reported from either method alone. Moreover, our approach efficiently suppresses adverse features of single-pass bulk spectral broadening. We use a burst mode Yb:YAG laser emitting pulses with 80 MW peak power that are enhanced to more than 1 GW after post-compression. With only 0.19 % rms pulse-to-pulse energy fluctuations, the technique exhibits excellent stability. Furthermore, we have measured state-of-the-art spectral-spatial homogeneity and good beam quality of M$^2 = 1.2$ up to a spectral broadening factor of 30. Due to the method's simplicity, compactness and scalability, it is highly attractive for turning a high-power picosecond laser into an ultrafast light source that generates pulses of only a few tens of femtoseconds duration.

Journal ArticleDOI
01 Dec 2021-PhotoniX
TL;DR: In this article, an incoherent continuous-wave (CW) optical field propagating in the fiber with normal dispersion is investigated, and the underlying physical mechanism is attributed to a novel interplay between group-velocity dispersion (GVD), self-phase modulation (SPM) and inverse four-wave mixing (IFWM), in which SPM and GVD are responsible for the first spectral broadening, while the following spectral recompression is due to the GVD-assisted IFWM.
Abstract: Interplay between dispersion and nonlinearity in optical fibers is a fundamental research topic of nonlinear fiber optics. Here we numerically and experimentally investigate an incoherent continuous-wave (CW) optical field propagating in the fiber with normal dispersion, and introduce a distinctive spectral evolution that differs from the previous reports with coherent mode-locked fiber lasers and partially coherent Raman fiber lasers [Nat. Photonics 9, 608 (2015).]. We further reveal that the underlying physical mechanism is attributed to a novel interplay between group-velocity dispersion (GVD), self-phase modulation (SPM) and inverse four-wave mixing (IFWM), in which SPM and GVD are responsible for the first spectral broadening, while the following spectral recompression is due to the GVD-assisted IFWM, and the eventual stationary spectrum is owing to the dominant contribution of GVD effect. We believe this work can not only expand the light propagation in the fiber to a more general case and help advance the physical understanding of light propagation with different statistical properties, but also benefit the applications in sensing, telecommunications and fiber lasers.

Journal ArticleDOI
TL;DR: In this article, a Ti:Sapphire amplifier with spectral broadening was used for nonlinear pulse compression in a compact multi-pass cell filled with argon and the results showed that the efficiency was limited to 45% mostly by losses in the mirrors of the cell.
Abstract: Compression of 42 fs, 0.29 mJ pulses from a Ti:Sapphire amplifier down to 8 fs (approximately 3 optical cycles) is demonstrated by means of spectral broadening in a compact multi-pass cell filled with argon. The efficiency of the nonlinear pulse compression is limited to 45 % mostly by losses in the mirrors of the cell. The experimental results are supported by 3-dimensional numerical simulations of the nonlinear pulse propagation in the cell that allow us to study spatio-spectral properties of the pulses after spectral broadening.

Journal ArticleDOI
TL;DR: In this article, the spectral broadening of 0.3 ps 515 nm laser pulse in a highly Raman-active BaWO4 crystal and fused silica demonstrates significantly different behavior with the incident pulse energy.
Abstract: Spectral broadening of 0.3 ps 515 nm laser pulse in a highly Raman-active BaWO4 crystal and fused silica demonstrates significantly different behavior with the incident pulse energy. While the broadening in fused silica is fairly symmetric with respect to the pump laser pulse wavelength, the Stokes wing broadening in the BaWO4 crystal is 2 times wider than that of anti-Stokes wing, the former demonstrating a step-like increase with the pulse energy. To the best of our knowledge, the obtained data are the first clear evidences of the following facts: (i) stimulated Raman scattering with sufficiently high efficiency of conversion to Stokes components slows down spectral broadening induced by self-phase modulation, and (ii) the mechanism of Kerr nonlinearity, which is responsible for self-phase modulation in BaWO4, is of orientational nature. The nonlinear refraction coefficient and its decay time following from our experiments with BaWO4 were estimated as n2≈6.4.10−15cm2/W and τNL≈0.35ps.

Journal ArticleDOI
TL;DR: In this paper, a series of quadruple perovskites Ca1+xCu3-xTi4O12 was scanned by different spectroscopic and microscopic techniques, and the results of positron annihilation spectroscopy to study the nature of the defects are consistent with the proposed defect-rich sample history.

Journal ArticleDOI
TL;DR: In this article, a proposal for additional temporal compression and peak power enhancement of intense (>TW/cm2) femtosecond laser pulses using two thin plane-parallel plates is presented.
Abstract: A proposal for additional temporal compression and peak power enhancement of intense (>TW/cm2) femtosecond laser pulses using two thin plane-parallel plates is presented. The first ultrathin plate (order of mm) induces spectral broadening due to self-phase modulation, and the second ultrathin plate (order of micron) corrects the spectral phase. The elimination of the negative dispersive multilayer coating from the scheme offers an improved laser-induced damage threshold for the post-compression process.

Journal ArticleDOI
TL;DR: In this article, the authors employed the depth sensitive slow positron Doppler broadening technique to characterise the positron diffusion in various near-surface layers of He+ implanted f/m steels.

Journal ArticleDOI
TL;DR: In this paper, the influence of transmutation rhenium on the irradiation-induced defects in tungsten, H+ and He+ irradiation of 50 keV with a fixed fluence of 1.5 cm−2 were conducted on WxRe (x = 0, 3, 5 and 25 wt.%) alloys, respectively.

Journal ArticleDOI
01 May 2021
TL;DR: The research led to the development of binary classifiers for classifying volunteers and patients into groups according to the functional state of microcirculation and the method was tested in healthy volunteers of different ages and patients with type 2 diabetes mellitus.
Abstract: A method and a device for digital laser Doppler flowmetry are proposed. An approach to signal processing based on analysis of the power spectrum amplitude distribution over Doppler broadening frequencies is suggested. A prototype of the device is presented; its technical characteristics and settings used in tests are described. The method was tested in healthy volunteers of different ages and patients with type 2 diabetes mellitus. The research led to the development of binary classifiers for classifying volunteers and patients into groups according to the functional state of microcirculation.

Journal ArticleDOI
29 Jul 2021
TL;DR: Positron annihilation spectroscopy using lifetime and Doppler broadening allows the characterization of the lithiation state in LiCoO2 thin film used in cathode of lithium-ion batteries as mentioned in this paper.
Abstract: Positron annihilation spectroscopy using lifetime and Doppler broadening allows the characterization of the lithiation state in LiCoO2 thin film used in cathode of lithium-ion batteries. The lifetime results reflect positron spillover because of the presence of graphite in between the oxide grains in real cathode Li-ion batteries. This spillover produces an effect in the measured positron parameters which are sensitive to delocalized electrons from lithium atoms as in Compton scattering results. The first component of the positron lifetime corresponds to a bulk-like state and can be used to characterize the state of charge of the cathode while the second component represents a surface state at the grain-graphite interface.

Journal ArticleDOI
TL;DR: In this paper, a phase-shifted long-period fiber grating (PS-LPFG) was proposed to suppress spectral broadening in a high-power fiber master oscillator power amplifier (MOPA) laser system.
Abstract: Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot. At present, research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser. However, the suppression of spectral broadening, caused by self-phase modulation or four-wave mixing, is still a challenging attribute to the close distance between the broadened laser and signal laser. If using a traditional fiber grating with only one stopband to suppress the spectral broadening, the signal power will be stripped simultaneously. Confronting this challenge, we propose a novel method based on phase-shifted long-period fiber grating (PS-LPFG) to suppress spectral broadening in a high-power fiber master oscillator power amplifier (MOPA) laser system in this paper. A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique. The resonant wavelength of the fabricated PS-LPFG is 1080 nm, the full width at half maximum of the passband is 5.48 nm, and stopband extinction exceeds 90%. To evaluate the performance of the PS-LPFG, the grating is inserted into the seed of a kilowatt-level continuous-wave MOPA system. Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%, providing an effective and flexible way for optimizing the output linewidth of high-power fiber MOPA laser systems.