Laser Plasma Research Articles

In-situ synthesis of dual-phase nitrides and multiple strengthening mechanisms in FeCoCrNiAl0.5 high entropy matrix composite coatings by laser cladding and plasma nitriding

To enhance the wear resistance of high entropy alloy (HEA) coatings and broaden their applications under extreme conditions, this study proposed an in-situ synthesis process of a dual-phase strengthened nitrides layer on laser cladded HEA coating. The microstructural evolution and mechanical properties of FeCoCrNiAl0.5 HEA coating by plasma nitriding were systematically investigated, revealing formation and strengthening mechanisms of nitrides. In comparison to the traditional nitrided substrate 38CrMoAl, the results showed that the nitrided HEA coating exhibited high hardness and wear resistance, characterized by dual-phase nitrides AlN+CrN due to the negative Gibbs free energy, negative nitride formation enthalpy and higher atomic specific surface areas. While only a single-phase iron nitride with lower hardness was obtained on the nitrided 38CrMoAl. The microhardness and wear mass loss of the nitrided HEA coating were 1167 HV and 0.435×10−6 mg/mm, respectively, which were 33.4% higher and 63.3% lower than those of the nitrided 38CrMoAl. The strengthening effects attributed to the refinement of dual-phase nitrides, interstitial solid solution by N atoms, dispersion strengthening by higher proportion of nitrides.

A wide-band, high-resolution semi-von Hamos spectrometer for K-shell multi-ionization atoms X-ray measurements

A wide-band, high-resolution vacuum semi-von Hamos spectrometer has been developed for analyzing the X-rays spectra of K-shell multi-ionization atoms. The spectrometer covers an energy dynamic range of 0.6 to 18 keV with a corresponding single exposure spectral bandwidth of 0.25–1.2 keV. This capability is achieved by the combination of different cylindrically bent crystals and an X-ray CCD detector mounted on a twistable bellows, allowing modulation of the Bragg angles from 27° to 47°. A detailed mathematical description is employed to understand the dependence of the geometrical parameters of the spectrometer on the imaging properties, energy spectrum bandwidth, resolving power, solid angle, and other relevant spectrometer characteristics. An energy calibration has been performed by using K X-rays generated by 10–30 keV electron beam interactions with solid KCl, CaF2 and Se targets. The spectrometer exhibits a resolving power better than 103, enabling the analysis of fine spectral structure of K X-ray transitions and the comparison of X-ray properties between pure elements and their compounds due to chemical effects. The spectrometer also finds applications in various fields requiring precise X-ray measurements, including synchrotron radiation experiments, tokamaks, laser plasma diagnostics and laboratory astrophysics.

Hall Effects and Diamagnetic Cavity Collapse during a Laser Plasma Cloud Expansion into a Vacuum Magnetic Field

Hall Effects and Diamagnetic Cavity Collapse during a Laser Plasma Cloud Expansion into a Vacuum Magnetic Field

Review of recent analytical advances in the spectroscopy of hydrogenic lines in plasmas

Abstract Broadening of hydrogenic spectral lines is an important tool in spectroscopic diagnostics of various laboratory and astrophysical plasmas. We review recent analytical advances in three areas. First, we review the analytical solution for the splitting of hydrogenic lines under the combination of a circularly polarized electromagnetic wave with a strong magnetic field. Practical applications of this solution relate to the spectroscopic diagnostic of the electron cyclotron waves and to the relativistic laser–plasma interactions. Second, we review analytical results concerning the Stark–Zeeman broadening of the Lyman-alpha (Ly-alpha) line in plasmas. These results allow for the Stark width of the Ly-alpha π-component to be used for the experimental determination of the ion density or of the root-mean-square field of a low-frequency electrostatic plasma turbulence in the situation where the Zeeman effect dominates over the Stark effects. Third, we review recent analytical advances in the area of the intra-Stark spectroscopy: three different new methods, based on the emergent phenomenon of the Langmuir-wave-caused structures (“L-dips”) in the line profiles, for measuring super-strong magnetic fields of the GigaGauss range developing during relativistic laser–plasma interactions. We also review the rich physics behind the L-dips phenomenon – because there was a confusion in the literature in this regard.

Cryogenic solid deuterium target formation to realize highly pure deuteron acceleration by high-intensity laser

In recent years, laser-driven neutron sources have attracted attention for their applications such as nondestructive analysis and the production of medical radioisotopes. One of the efficient neutron production methods is the use of the 9Be(d, n)10B reaction on a beryllium target with deuterons accelerated by laser–plasma interactions, since this is an exothermic reaction. For efficient deuteron acceleration, we have developed a formation system for solid deuterium targets. A millimeter thick solid deuterium target can be formed with the system. Before the laser shot, the solid deuterium target in the laser chamber can be mechanically moved to the laser irradiation point. We have demonstrated deuteron acceleration by the LFEX laser, and a highly pure deuteron pulse with energies of up to 6.2 MeV was measured with a Thomson parabola ion spectrometer.

A computational model to understand the interaction of nanosecond pulsed laser with ultra-thin SiN[formula omitted] layer-coated silicon substrate

Nanosecond lasers can be used for the selective ablation of ultra-thin SiNx layer (80–100 nm) coated on a silicon substrate with applications in the fabrication of PERC solar cells. Experiments reveal that the ablation process can occur in different regimes with material removal in solid, liquid, vapor, and explosion forms. This study investigates the different regimes for single pulse ablation through a physics-based model developed using the finite volume method in Ansys Fluent. The model accounts for various physical phenomena, including laser heating, melting, thermal expansion, thermal decomposition, Marangoni convection, vaporization, plasma formation, melt expulsion, and phase explosion. Experiments were conducted using Nd: YVO4 laser (λ=532 nm, pulse duration = 50 ns), and the measured single pulse crater profiles are in excellent agreement with the model predictions over a broad range of laser fluence. Results show that the SiNx layer breaks due to the thermal expansion of the underlying silicon at lower fluences (3.05–3.35 J/cm2) in a very narrow range. Above this fluence range lies another narrow range (3.35–5.55 J/cm2) wherein the SiNx layer is thermally decomposed into silicon and nitrogen, and craters are formed due to Marangoni convection in the melt pool formed. Ablation due to vaporization occurs in a broad fluence range (5.55–8.4 J/cm2), causing deeper ablation depths and material deposition at the crater edge. At higher fluences (¿8.4 J/cm2), explosive boiling occurs due to homogeneous nucleation, resulting in much higher ablation depths (¿1.6μm), broader crater widths, and poor surface finish. This model provides an understanding of different material removal regimes in laser ablation of SiNx-coated silicon.

Analysis of Plasma Dynamics in He-Ne Lasers with Different Gas Ratios

He-Ne lasers play a crucial role in ultra-precision measurement and optical sensing across various fields. For many applications based on He-Ne lasers, a higher output power is required to enhance the accuracy and signal-to-noise ratios of the associated optical measurements. However, conventional methods to increase the output power by reducing the diameter of the He-Ne laser discharge capillary inevitably result in higher diffraction losses and constrain the lasing performance. Here, we propose an approach to enhance laser pumping efficiency and output power through optimizing the ratios of He and Ne gasses. The validity of our proposal has been confirmed by both numerical simulations of He-Ne laser plasma discharge processes and experimental demonstrations, showing that the optimal gas ratio increases with the capillary diameter and total gas pressure.

Ultrafast random polarization beam smoothing driven by counter-rotating wavefronts via the optical Kerr effect

We propose an ultrafast random polarization smoothing scheme to achieve ultrafast speckle movement and polarization randomization of the focal spot. In the scheme, each beamlet in a laser quad is driven by a rotating petal-like wavefront, giving rise to the ultrafast redistribution of the speckles within the focal spot. The rotating wavefront is induced by an optical Kerr medium pumped by a laser beam with rotating intensity distribution that is generated by the superposition of two Laguerre–Gaussian beams carrying conjugate vortex phase and frequency shift. In addition, by properly selecting the topological charges of the pump beams and polarization states of the beamlets, the beamlets in a quad can be divided into two sets with counter-rotating wavefronts and orthogonal polarizations, which further randomizes the polarization of the focal spot. Results indicate that the proposed scheme can reduce the contrast by more than 70% and the degree of polarization by more than 75% within several picoseconds, by utilizing the rotating phase pumped by two Laguerre-Gaussian beams with a peak intensity of 0.18GW/cm2 and a frequency shift of 1 THz. The ultrafast random polarization smoothing scheme is expected to suppress the growth of Laser Plasma Instabilities (LPIs) including the filamentation and backscatter in indirect-drive inertial confinement fusion (ICF) facilities.

EUV photoabsorption spectrum of N-like fluorine using dual laser plasma technique

Employing the dual laser plasma technique, we measured the extreme ultraviolet (EUV) photoabsorption spectrum of F2+ ions, spanning the energy range from 53 to 93 eV with an energy resolution (E/ΔE) of 866. The measured spectrum is carefully analyzed by comparing with the available reference data and theoretical calculation using the Cowan code. We identify prominent transitions to the Rydberg series 2s22p2ns/nd and 2s2p3np from the ground level and remarkable transitions to the 2s22p2(1D)nd2D states from the 2s22p32D metastable level. Transition energies and line profile parameters are determined by fitting the identified absorption features. The calibration of the spectrometer with well-known transitions allows us to provide line positions for well-resolved resonances with an uncertainty of 20 meV. The reported experimental data of F2+ significantly contribute to the fundamental atomic database, offering valuable benchmarks for theoretical calculations with potential applications in astrophysics and plasma sciences.

Characterization of experimental and simulated micrometer-scale soft x-ray-emitting laser plasmas: Toward predictive radiance calculations

Experimentally generated and simulated soft x-ray plasma images and spectra from 1064 nm-driven laser-produced plasmas from slab tin are presented. Produced are small, micrometer-scale emission volumes with principle imaged emission lying between 1.2 and 2.5 nm. Experimental images of the soft x-ray emission of these plasmas are generated using a pinhole imaging system, which enables spatial characterization of the plasmas, and a simple transmission grating spectrometer with a 100 nm pitch grating is used to facilitate the spectral characterization of these plasmas. Plasmas are simulated under similar experimental conditions to those used with the single-fluid, single-temperature radiation-hydrodynamics code RALEF-2D. Coupling the simulation output with optical modeling methods demonstrates its promise as a capability for modeling the spatial and spectral behavior of soft x-ray-emitting tin plasmas at such scales and laser energies.

Tailored mesoscopic plasma accelerates electrons exploiting parametric instability

Laser plasma electron acceleration from the interaction of an intense femtosecond laser pulse with an isolated microparticle surrounded by a low-density gas is studied here. Experiments presented here show that optimized plasma tailoring by introducing a pre-pulse boosts parametric instabilities to produce MeV electron energies and generates electron temperatures as large as 200 keV with the total charge being as high as 350 fC/shot/sr, even at a laser intensity of a few times 1016 Wcm−2. Corroborated by particle-in-cell simulations, these measurements reveal that two plasmon decay in the vicinity of the microparticle is the main contributor to hot electron generation.

On parallel laser beam merger in plasmas

Self-focusing instability is a well-known phenomenon of nonlinear optics, which is of great importance in the field of laser–plasma interactions. Self-focusing instability leads to beam focusing and, consequently, breakup into multiple laser filaments. The majority of applications tend to avoid a laser filamentation regime due to its detrimental role on laser spot profile and peak intensity. In our work, using nonlinear Schrödinger equation solver and particle-in-cell simulations, we address the problem of interaction of multiple parallel beams in plasmas. We consider both non-relativistic and moderately relativistic regimes and demonstrate how the physics of parallel beam interaction transitions from the familiar self- and mutual-focusing instabilities in the non-relativistic regime to a moderately relativistic regime, where an analytical description of filament interaction is not available.

Characterization of a UV-USP Laser Grooving Process Combined with Plasma Dicing to Support Next Generation Advanced Packaging Trends

In this study, we investigated and characterized the combined process flow of the UV-USP (ultra-short pulse) laser grooving and plasma dicing wafer singulation technologies and discussed the impact on subsequent hybrid bonding steps. We benchmarked UV-USP laser grooving against UV-nanosecond laser grooving to enable plasma dicing by evaluation of imaging and die strength measurements. The results showed the advantages of the UV-USP laser grooving combined with plasma dicing for the current and future semiconductor production flows.

Efficient Magnetic Vortex Acceleration by femtosecond laser interaction with long living optically shaped gas targets in the near critical density plasma regime

We introduce a novel, gaseous target optical shaping laser set-up, capable to generate short scale length, near-critical target profiles via generated colliding blast waves. These profiles are capable to maintain their compressed density for several nanoseconds, being therefore ideal for laser-plasma particle acceleration experiments in the near critical density plasma regime. Our proposed method overcomes the laser-target synchronization limitations and delivers energetic protons, during the temporal evolution of the optically shaped profile, in a time window of approximately 2.5 ns. The optical shaping of the gas-jet profiles is optimised by MagnetoHydroDynamic simulations. 3D Particle-In-Cell models, adopting the spatiotemporal profile, simulate the 45 TW femtosecond laser plasma interaction to demonstrate the feasibility of the proposed proton acceleration set-up. The optical shaping of gas-jets is performed by multiple, nanosecond laser pulse generated blastwaves. This process results in steep gradient, short scale length plasma profiles, in the near critical density regime allowing operation at high repetition rates. Notably, the Magnetic Vortex Acceleration mechanism exhibits high efficiency in coupling the laser energy into the plasma in the optically shaped targets, resulting to collimated proton beams of energies up to 14 MeV.

Effects of Nd: YAG LASER irradiation and O2 plasma on the adhesive performance of poly-ether-ether-ketone (PEEK)

PurposeTo evaluate the effects of neodymium-doped yttrium aluminum garnet (Nd: YAG) LASER irradiation and oxygen (O2) plasma on the adhesive performance of polyether ether ketone (PEEK) and resin adhesive. MethodsNd: YAG LASERs of varying powers and O2 plasma for different durations were used to modify PEEK. A total of 168 PEEK specimens were randomly divided into seven groups (n = 24/group): (A) Control group: untreated PEEK, (B) L0.75 group: PEEK modified with 0.75 W Nd: YAG LASER, (C) L1 group: PEEK modified with 1.0 W Nd: YAG LASER, (D) L1.25 group: PEEK modified with 1.25 W Nd: YAG LASER, (E) P15 group: PEEK modified with 15 min of O2 plasma, (F) P25 group: PEEK modified with 25 min of O2 plasma, and (G) P35 group: PEEK modified with 35 min of O2 plasma. The surface characteristics of the materials were comprehensively analyzed using a scanning electron microscope (SEM), profilometer, energy-dispersive spectrometer (EDS), and contact angle tester. The adhesive specimens were bonded with Variolink N resin adhesive in all groups and each group was further divided into two subgroups (n = 12/group): (a) water storage for 56 h at 37 °C and (b) thermal cycling 5000 times. Shear bond strength (SBS) was tested using a universal testing machine, and the fracture modes were observed using an automated chemiluminescence analysis system to assess the effects of Nd: YAG LASER and O2 plasma on the bond strength of PEEK to resin adhesive. ResultsBoth Nd: YAG LASER and O2 plasma treatments altered the surface characteristics of PEEK and significantly increased the SBS between PEEK and Variolink N resin adhesive. The L0.75 group (Nd: YAG LASER) and the P35 group (O2 plasma) achieved the highest SBS, respectively. Furthermore, the SBS of the L0.75 group was higher than that of the P35 group. Following thermal cycling, SBS values decreased compared to the water storage subgroups. The fracture modes of the specimens in each group were predominantly interfacial and mixed, with no cohesive fractures observed. ConclusionsNd: YAG LASER irradiation and O2 plasma treatments can improve the SBS between PEEK and resin adhesive, with the 0.75 W Nd: YAG LASER being the preferred treatment method.

Collective coherent emission of electrons in strong laser fields and perspective for hard x-ray lasers

Coherent motion of particles in a plasma can imprint itself on radiation. The recent advent of high-power lasers—allowing the nonlinear inverse Compton-scattering regime to be reached—has opened the possibility of looking at collective effects in laser–plasma interactions. Under certain conditions, the collective interaction of many electrons with a laser pulse can generate coherent radiation in the hard x-ray regime. This perspective paper explains the limitations under which such a regime might be attained.

Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion

Parameter estimation using observables is a fundamental concept in the experimental sciences. Mathematical models that represent the physical processes can enable reconstructions of the experimental observables and greatly assist in parameter estimation by turning it into an optimization problem which can be solved by gradient-free or gradient-based methods. In this work, the recent rise in flexible frameworks for developing differentiable scientific computing programs is leveraged in order to dramatically accelerate data analysis of a common experimental diagnostic relevant to laser–plasma and inertial fusion experiments, Thomson scattering. A differentiable Thomson-scattering data analysis tool is developed that uses reverse-mode automatic differentiation (AD) to calculate gradients. By switching from finite differencing to reverse-mode AD, three distinct outcomes are achieved. First, gradient descent is accelerated dramatically to the extent that it enables near real-time usage in laser–plasma experiments. Second, qualitatively novel quantities which require O(103) parameters can now be included in the analysis of data which enables unprecedented measurements of small-scale laser–plasma phenomena. Third, uncertainty estimation approaches that leverage the value of the Hessian become accurate and efficient because reverse-mode AD can be used for calculating the Hessian.

Evaluating Mass Spectrometry-Based Hydroxyl Radical Protein Footprinting of a Benchtop Flash Oxidation System against a Synchrotron X-ray Beamline.

Hydroxyl radical protein footprinting (HRPF) using synchrotron X-ray radiation (XFP) and mass spectrometry is a well-validated structural biology method that provides critical insights into macromolecular structural dynamics, such as determining binding sites, measuring affinity, and mapping epitopes. Numerous alternative sources for generating the hydroxyl radicals (•OH) needed for HRPF, such as laser photolysis and plasma irradiation, complement synchrotron-based HRPF, and a recently developed commercially available instrument based on flash lamp photolysis, the FOX system, enables access to laboratory benchtop HRPF. Here, we evaluate performing HRPF experiments in-house with a benchtop FOX instrument compared to synchrotron-based X-ray footprinting at the NSLS-II XFP beamline. Using lactate oxidase (LOx) as a model system, we carried out •OH labeling experiments using both instruments, followed by nanoLC-MS/MS bottom-up peptide mass mapping. Experiments were performed under high glucose concentrations to mimic the highly scavenging conditions present in biological buffers and human clinical samples, where less •OH are available for reaction with the biomolecule(s) of interest. The performance of the FOX and XFP HRPF methods was compared, and we found that tuning the •OH dosage enabled optimal labeling coverage for both setups under physiologically relevant highly scavenging conditions. Our study demonstrates the complementarity of FOX and XFP labeling approaches, demonstrating that benchtop instruments such as the FOX photolysis system can increase both the throughput and the accessibility of the HRPF technique.

Influence of Non-Invasive Zirconium Oxide Surface Treatment on Phase Changes

The aim of the research was to find a zirconia treatment method that would reduce or minimize the transformation from the tetragonal phase to the monoclinic phase. Background: Yttria-stabilized zirconia is increasingly chosen for the base of permanent prosthetic restorations. To achieve a good bond between the prosthetic cup and the veneer material, the material must be treated to achieve surface development. This is a mechanical process, during which an unfavorable transformation from the tetragonal into the monoclinic phase takes place, which leads to the weakening of the internal structure of zirconium dioxide, and later damages the prosthetic restoration. Methods: The tested material consisted of cylindrical samples of 3Y-TZP CeramillZi zirconium oxide, which were sintered after cutting out from the block. After sintering, the samples were subjected to the following types of processing: laser structuring, chemical etching and plasma etching. After the surface treatments, the samples were subjected to diffraction tests to determine the phase composition. Next, the wettability was tested to determine the surface free energy. Results: On the basis of the conducted tests, it was noticed that the applied treatments caused a phase transformation from the tetragonal to the monoclinic phase. After the process of chemical etching, the range of the monoclinic phase for the sample was 5%; after plasma etching, it was 8%, and after laser structuring, it was 2%. In addition, post-surface free energy studies have shown that zirconia is wetted better with an apolar than a polar liquid. Conclusions: The obtained results indicate that the transformation was minimized with the treatments we applied; that is why they are called non-invasive methods. According to the literature data, depending on the parameters of the sandblasting process, the percentage of the monoclinic phase in the treated surfaces ranges from 22% to 52%, which confirms the above-mentioned conclusion.

Investigation of laser plasma instabilities driven by 527 nm laser pulses relevant for direct drive inertial confinement fusion

We report on a study of laser plasma instabilities with 527 nm laser pulses in an intensity range of 0.5×1013−1.1×1015 Wcm−2 and plasma parameters entering a regime that is relevant for direct drive inertial confinement fusion. Using the kilojoule high repetition rate L4n laser at the Extreme Light Infrastructure—Beamlines, more than 1300 shots were collected, and the onset and the growth of stimulated Brioullin scattering (SBS) and stimulated Raman scattering (SRS) were studied with a high confidence level. The measured onset intensities are 0.2×1014 Wcm−2 for SBS and 1.4×1014 Wcm−2 for SRS. At the maximum intensity, the total fraction of backscattered energy reaches 2.5% for SBS and 0.1% for SRS. These results are of high relevance for advanced concepts for inertial fusion energy, which rely on the use of 527 nm laser light to drive the implosion of the fuel target, and in particular, they can be used as a benchmark for advanced simulations.