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Laser-Induced Breakdown Spectroscopy Assisted by Machine Learning for Plastics/Polymers Identification
摘要： In the present work, Laser-Induced Breakdown Spectroscopy (LIBS) is used for the discrimination/identification of different plastic/polymeric samples having the same polymeric matrix but containing different additives (as e.g., fillers, flame retardants, etc.). For the classification of the different plastic samples, some machine learning algorithms were employed for the analysis of the LIBS spectroscopic data, such as the Principal Component Analysis (PCA) and the Linear Discriminant Analysis (LDA). The combination of LIBS technique with these machine learning algorithmic approaches, in particular the latter, provided excellent classification results, achieving identification accuracies as high as 100%. It seems that machine learning paves the way towards the application of LIBS technique for identification/discrimination issues of plastics and polymers and eventually of other classes of organic materials. Machine learning assisted LIBS can be a simple to use, efficient and powerful tool for sorting and recycling purposes.
关键词： laser-induced breakdown,polymers,LIBS,machine learning,identification of polymers,laser produced plasmas
更新于2025-09-16 10:30:52
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Lorenz Type Behaviors in the Dynamics of Laser Produced Plasma
摘要： An innovative theoretical model is developed on the backbone of a classical Lorenz system. A mathematical representation of a differential Lorenz system is transposed into a fractal space and reduced to an integral form. In such a conjecture, the Lorenz variables will operate simultaneously on two manifolds, generating two transformation groups, one corresponding to the space coordinates transformation and another one to the scale resolution transformation. Since these groups are isomorphs various types isometries become functional. The Lorenz system was further adapted to describe the dynamics of ejected particles as a result of laser matter interaction in a fractal paradigm. The simulations were focused on the dynamics of charged particles, and showcase the presence of current oscillations, a heterogenous velocity distribution and multi-structuring at different interaction scales. The theoretical predictions were compared with the experimental data acquired with noninvasive diagnostic techniques. The experimental data confirm the multi-structure scenario and the oscillatory behavior predicted by the mathematical model.
关键词： plasma structuring,fractal analysis,laser produced plasmas,ionic oscillations,Lorenz system
更新于2025-09-16 10:30:52
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Neutron production from thermonuclear reactions in laser-generated plasmas
摘要： The production of intense neutron beams via thermonuclear reactions in laser-generated plasmas is investigated theoretically. So far, state-of-the-art neutron beams are produced via laser-induced particle acceleration leading to high-energy particle beams that subsequently interact with a secondary target. Here, we show that neutron beams of two orders of magnitude narrower bandwidth can be obtained from thermonuclear reactions in plasmas generated by Petawatt-class lasers. The intensity of such neutron beams is about one or two orders of magnitude lower than the one of the state-of-the-art laser-driven neutron beams. We study to this end the reaction 2H(d, n)3He in plasmas generated by Petawatt-class lasers interacting with D2 gas jet targets and CD2 solid-state targets. The results also show the possibility of direct measurements of reaction rates at low temperatures of astrophysical interest. In addition, the use of CD2 solid-state targets can also lead to great enhancements of the plasma screening compared to the case of D2 gas jet targets, opening new possibilities to study this so far unsolved issue in the field of astrophysics.
关键词： laser-generated plasmas,neutron production,Petawatt-class lasers,plasma screening effects,thermonuclear reactions
更新于2025-09-16 10:30:52
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Numerical simulations to study turbulent magnetic field amplification by nonlinear interaction of high-power laser and kinetic Alfvén waves in laboratory and astrophysical plasmas
摘要： The model contouring the dynamics of transient nonlinear interaction between the high-frequency extraordinary-elliptically polarized laser (HFXPL) and low-frequency kinetic Alfvén wave (LFKAW) dynamics in the magnetized plasma is the focal point of the present investigation. The quasistatic ponderomotive force driven by the HFXPL pump induces density cavitation and humps in the low-frequency kinetic Alfvén wave. In order to study the intricate localized structures of HFXPL pump waves that evolve with time, the requisite dimensionless equations of the coupled system (HFXPL and LFKAW) are evaluated by using numerical methods in the nonlinear stage. The typical scale sizes of these structures in the early phase are ≈9 μm, and the typical time to grow is ≈10 ps. The ensemble-averaged magnetic power spectra are also presented, indicating energy cascade. The rendered investigations follow direct relevance to the experimental observations and are imperative in understanding turbulence in astrophysical scenarios.
关键词： kinetic Alfvén waves,high-power laser,astrophysical plasmas,laboratory plasmas,nonlinear interaction,turbulent magnetic field amplification
更新于2025-09-12 10:27:22
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Effect of laser polarization on the electron dynamics and photon emission in near-critical-density plasmas
摘要： When the laser intensity approaches 1022 W=cm2, the recoil force from high-energy photons radiated by relativistic electrons becomes important and may be comparable with the ponderomotive force of the laser pulse. As a result, the electron dynamics is modified greatly. By using particle-in-cell simulations, we show that the polarization of laser pulse has significant influence on the electron behaviors and accompanying radiation in near-critical-density plasmas. Due to the RR force and the pinching effect of self-generated magnetic field, it turns out that much more electrons are trapped in the center of a circularly-polarized (CP) laser pulse than that of a linearly-polarized (LP) laser pulse. Meanwhile, the (cid:13)(cid:0)photon emission is characterized by a two-peak structure in the LP case, while it is dominated in the forward direction in the CP case where electrons keep moving forward along the laser propagating direction. These may serve as a potential signature for radiation trapping effect in forthcoming experiments to be carried out on petawatt (PW) laser facilities.
关键词： laser polarization,photon emission,electron dynamics,radiation reaction force,near-critical-density plasmas,particle-in-cell simulations
更新于2025-09-12 10:27:22
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CdTe:Sn thin films deposited by the simultaneous laser ablation of CdTe and Sn targets
摘要： CdTe:Sn thin films were grown by pulsed laser deposition on glass substrates at room temperature. The study of the changes in the chemical, structural and optical properties of the films as a function of the density of Sn ions calculated from Langmuir planar probe measurements is presented. Four films were grown by the simultaneous ablation of CdTe and Sn targets in vacuum. The Sn ion density was modified by varying the fluence on the Sn target, while the CdTe plasma density was kept constant for all the deposits. The chemical composition was analyzed by XPS, where a dependence of the Sn incorporation into the CdTe lattice, on the Sn ion plasma density was demonstrated. The crystalline structure analysis by XRD showed a hexagonal structure for all the films. When the CdTe and Sn plasmas were combined, a preferential orientation in the plane (110) was observed for the resulting films. Furthermore, as Sn plasma density increased, the intensity of the (110) peak increased as well, suggesting that crystalline re-orientation is an effect of Sn incorporated into the CdTe lattice. Vibrational behavior was analyzed by Raman spectroscopy. A vibrational mode appeared at 118 cm-1 and was related to a Sn-Te vibration, suggesting the incorporation of substitutional Sn into the CdTe lattice. The Sn-Te bonding was confirmed by XPS by the appearance of signals centered at 485 and 494 eV, which correspond to Sn2+ in SnTe. Thin films thicknesses values were between 320 and 460 nm increasing with Sn ion density. The band gap calculated using UV-Vis spectrophotometry, resulted in values ranging from 1.42 to 1.46 eV. PL measurements showed a slight blue shift of the near-edge emission as Sn plasma density increased.
关键词： PLD,CdTe:Sn,plasmas
更新于2025-09-12 10:27:22
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Characterization of a 100 micrometer-scale cryogenically cooled gas jet for near-critical density laser-plasma experiments
摘要： We present the design and characterization of a thin, high density pulsed gas jet for use in the study of near critical laser plasma interactions with ultrashort Ti:sapphire laser pulses. The gas jet uses a range of capillary nozzles with inner diameters between 50 and 150 μm and is operated in the sonic regime. Cryogenic cooling of the gas valve body to ?160 ○C provides the necessary density enhancement for reaching overcritical plasma densities at λ = 800 nm (Ncr ≈ 1.7 × 1021 cm?3) using hydrogen gas at jet backing pressures below 1000 psi. Under certain conditions, fast expansion of the gas from a nozzle can lead to formation of clusters; here, we use our previously demonstrated all-optical method to estimate the cluster mean size and density. For the jets studied here, we find that cluster formation only begins at distances from the nozzle exit greater than a few times the nozzle orifice diameter.
关键词： laser-plasma interactions,cluster formation,gas jet,high density plasmas,cryogenic cooling
更新于2025-09-12 10:27:22
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Determining a Line Strength in the ν <sub/>3</sub> Band of the Silyl Radical Using Quantum Cascade Laser Absorption Spectroscopy
摘要： Silane (SiH4) plasmas are widely used for the deposition of hydrogenated amorphous silicon (a-Si:H) films. Nevertheless, the chemical processes governing film deposition are still incompletely understood. Moreover, there is still no general method available to determine the absolute concentration of the silyl radical (SiH3), which is the accepted chemical precursor of a-Si:H films. In this study, a 10% silane in helium RF plasma was spectroscopically investigated between 2085 and 2175 cm?1 using an external cavity quantum cascade laser (EC-QCL) based spectrometer. This led to the identification of 4 distinct species from their absorption features: SiH4, disilane (Si2H6), SiH3, and an unassigned short-lived species. Furthermore, 17 absorption features of SiH3 were identified and unambiguously assigned. Fast spectral scanning of selected absorption features belonging to the four species in a 10 Hz pulsed RF plasma enabled the measurement and interpretation of their temporal behavior in terms of plausible chemical reactions involving silicon containing species. By quantitatively measuring the decay of the SiH3 a ← a pP4 (5) transition at 2151.3207 cm?1 after the discharge was stopped, its line strength (S) was determined to be (7.5 ± 5.5) × 10?20 cm2 cm?1 mol?1.
关键词： quantum cascade laser absorption spectroscopy,hydrogenated amorphous silicon,Silane plasmas,line strength,silyl radical
更新于2025-09-12 10:27:22
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High-order harmonic generation using quasi-phase matching and two-color pump in the plasmas containing molecular and alloyed metal sulfide quantum dots
摘要： As high-order harmonic emitters, quantum dots are produced through laser-induced plasmas. Subsequently, we generate high-order harmonics with 800-nm and 30-fs pulses from laser-produced plasmas containing quantum dots of different metal sulfides (Ag2S, CdS, and Cd0.5Zn0.5S). The high-order harmonic generation is analyzed using different approaches, including two-color (800 nm + 400 nm) pump, application of alloyed quantum dots, and quasiphase matching of interacting waves. We discuss the self-phase modulation induced splitting of harmonics, the difference in the application of thick and thin crystals for second harmonic (400 nm) emission during two-color pumping of the quantum dot plasma, the spatial modulation of the quantum dot plasma for quasiphase matching, and the comparison of harmonic yields from monomer and quantum dot plasmas. This study allows us to determine the mechanisms of coherent extreme ultraviolet radiation generation using a few nanometer-sized emitters as well as optimal methods for further enhancing the high-order harmonic generation efficiency.
关键词： laser-produced plasmas,quantum dots,high-order harmonic generation,quasiphase matching,two-color pump
更新于2025-09-12 10:27:22
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Polarization of fluorescence radiation following electron impact excitation of ions immersed in strongly coupled plasmas
摘要： An investigation on the electron impact excitation and subsequent radiative decay process of He-like Fe24t ions immersed in strongly coupled plasmas is made, using the 1s2p 3;1P1 ! 1s2 1S0 characteristic lines as an example. The shielded nuclear potential of the uniform electron gas model (UEGM) type experienced by the electron is parameterized by the ion-sphere radius. For the target structure, accuracies of wave functions are justified by evaluating the energies of the relevant states. To serve as an independent check of the results, self-consistent calculations are carried out using the multiconfiguration Dirac-Fock relativistic configuration interaction method incorporating the same potential. For the impact excitation process, the UEGM potential is also employed to screen the projectile electron from the nucleus and target electrons. A distorted-wave method in the framework of the relativistic theory is developed to include the effect of plasma background, in which the continuum wave function of the projectile electron is evaluated by solving numerically the modified Dirac equations. The plasma effects on the total excitation cross section, magnetic sublevel cross section, and linear polarization of fluorescence radiation are investigated. The comparison with the available theoretical and experimental results is satisfactory.
关键词： UEGM potential,linear polarization,He-like Fe24t ions,electron impact excitation,strongly coupled plasmas,radiative decay
更新于2025-09-12 10:27:22