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A flat-field soft X-ray spectrometer for X-ray absorption spectroscopy measurement of warm dense matter
摘要： A flat-field soft X-ray spectrograph operating in the spectral range of 250–1240 eV was designed and built for warm dense matter and high-energy density plasma physics. It employs a grazing incidence toroidal mirror as a focusing optic, an aberration-corrected variable line spacing concave grating with 2400 lines/mm as a dispersive element, and a charge coupled device as an X-ray detector. The dispersion and energy resolution are calibrated with a high-power laser-produced plasma and X-ray free electron laser sources. A resolving power over 370 was achieved over the entire spectral range. A super broadband spectrum in the range of 250–1000 eV was measured from the laser-produced bismuth plasma. The signal-to-noise of 130 was obtained with an average of 10 pulses. These results demonstrate the capability of the spectrograph for single laser shot based experiments for warm dense matter and high energy density plasma research.
关键词： soft x-ray spectrometer,laser plasma,warm dense matter,x-ray spectroscopy,high power laser
更新于2025-09-23 15:23:52
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Electronic parametric instabilities of an ultrarelativistic laser pulse in a plasma
摘要： Electronic parametric instabilities of an ultrarelativistic circularly polarized laser pulse propagating in underdense plasmas are studied by numerically solving the dispersion relation which includes the effect of the radiation reaction force in laser-driven plasma dynamics. Emphasis is placed on studying the different modes in the laser-plasma system and identifying the absolute and convective nature of the unstable modes in a parameter map spanned by the normalized laser vector potential and the plasma density. Implications for the ultraintense laser-plasma experiments are pointed out.
关键词： radiation reaction force,electronic parametric instabilities,laser-plasma system,plasma,ultrarelativistic laser pulse
更新于2025-09-23 15:21:01
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Plasma Science and Technology - Progress in Physical States and Chemical Reactions || Plasma-Enhanced Laser Materials Processing
摘要： In the last few years, the combination of laser irradiation with atmospheric pressure plasmas, also referred to as laser–plasma hybrid technology, turned out to be a powerful technique for different materials processing tasks. This chapter gives an overview on this novel approach. Two methods, simultaneous and sequential laser-plasma process‐ ing, are covered. In the first case, both the plasma and the laser irradiation are applied to the substrate at the same time. Depending on the process gas and the discharge type, the plasma provides a number of species that can contribute to the laser process plasma- physically or plasma-chemically. Sequential plasma-enhanced laser processing is based on a plasma-induced modification of essential material properties, thus improving the coupling of laser energy into the material during subsequent laser ablation. Simultane‐ ous plasma-assisted laser processing allows increasing the efficiency of a number of dif‐ ferent laser applications such as cleaning, microstructuring, or annealing processes. Sequential plasma-assisted laser processing is a powerful method for the processing of transparent media due to a reduction in the laser ablation threshold and an increase in the ablation rate at the same time. In this chapter, the possibilities, underlying mecha‐ nisms, performance, and limits of the introduced approaches are presented in detail.
关键词： Laser-plasma-hybrid techniques,microstructuring,atmospheric pressure plasma,modification,cleaning
更新于2025-09-23 15:21:01
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Effects of continuous phase plate on plasma corona homogeneity and laser-plasma instabilities in experiments with three target materials
摘要： Corona homogeneity and spectra of scattered light and hot electrons produced by laser-plasma instabilities inside laser-produced plastic, aluminum, and gold plasmas were investigated with and without the use of continuous phase plate (CPP) to the laser beam. Improvement of the corona homogeneity was observed for all three materials after applying CPP, while the inhibition of the intensity of backward-scattered light and the amount of emitted hot electrons was not always synchronous for different materials, which is interpreted as a result of the changes in thresholds of the stimulated Raman scattering (SRS) and the two-plasmon decay (TPD) instability before and after the application of CPP. By comparing the changes of SRS scattered light intensity with the amount of hot electrons in different kinetic energy ranges for all three target materials in our experiments, we conclude that SRS is more responsible for the diagnosed hot electrons between 50–150 keV, and those above 150 keV should be generated by TPD, which could be explained by the difference in phase velocity of electron plasma waves between SRS and TPD calculated from measured and simulated parameters of corona and laser-plasma instabilities.
关键词： hot electrons,plasma corona homogeneity,laser-plasma instabilities
更新于2025-09-23 15:21:01
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Control of electron beam energy-spread by beam loading effects in a laser-plasma accelerator
摘要： We present experimental results from a laser wakefield electron accelerator driven by 70 TW ultrashort laser pulses in Helium and Helium–Nitrogen gaseous plasmas with two different Nitrogen concentrations, showing distinct electron-beam qualities. In order to get a clear view of the involved phenomenon, two-dimensional particle-in-cell simulations are performed which not only agreed with the experimental results but also provided an investigation on the evolution of accelerating structures. The experimental and simulation results depict that the beam loading effect can strongly modify the longitudinal accelerating electric field of the wake wave, imposing diametrically opposite effects on the final electron-beam qualities, especially the energy-spread, in the Helium–Nitrogen gas mixtures with different Nitrogen concentrations. In the Helium–Nitrogen-mixed plasma with a lower Nitrogen concentration (0.5%), if appropriately controlled, the beam loading effect can be employed to flatten the accelerating electric field for reducing the electron-beam energy spread. In contrast, in the Helium–Nitrogen-mixed plasmas with a higher Nitrogen concentration (5%), the accelerating electric field of the wake is locally reversed by the self-fields of the overloaded electron bunch, and the correspondingly generated negative-slope region of electric field increases the electron-beam energy-spread.
关键词： experimental laser plasma acceleration,ionization injection,laser wakefield acceleration
更新于2025-09-23 15:21:01
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Parametric study of ultra-intense laser interaction with uniform and nano-porous near-critical plasmas
摘要： Responses of the uniform near-critical plasma (UNCP) and nano-porous near-critical plasma (NPNCP) upon interaction with a short-intense laser have been scrutinized using two-dimensional (2D) particle-in-cell simulations. Maximum proton energy variation by the deposition of uniform and nano-porous layers in front of a solid target for a wide range of laser intensities (normalized amplitude a0 = 5–25) and average densities of the front layer ne = 0.3 ? 3nc (where nc is the critical density) has been parametrically studied. It is found that the proton maximum energy for the front layers with sub-10 μm thicknesses is independent of the target porosity and density. However, in the relatively thick targets, the nano-porous structure decreases the laser energy absorption and, subsequently, the maximum proton energy compared to the uniform one. The results indicate that by employing UNCPs instead of NPNCPs, at the moderate laser intensity, the maximum proton energy reveals a 23% enhancement. This increment could be explained by rapid self-focusing of the laser pulse and dominant direct laser electron acceleration regime on the well-formed plasma channel in the UNCP layer. However, in the case of NPNCPs, the laser scattering from the plasma structure makes it less intense and more disordered, which influences the efficient laser energy coupling to the electrons.
关键词： proton acceleration,near-critical plasmas,particle-in-cell simulations,ultra-intense laser,laser-plasma interaction
更新于2025-09-23 15:21:01
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Self-focusing of UV radiation in 1 mm scale plasma in a deep ablative crater produced by 100 ns, 1 GW KrF laser pulse in the context of ICF
摘要： Experiments at the GARPUN KrF laser facility and 2D simulations using the NUTCY code were performed to study the irradiation of metal and polymethyl methacrylate (PMMA) targets by 100 ns UV pulses at intensities up to 5 3 1012 W cm?2. In both targets, a deep crater of length 1 mm was produced owing to the 2D geometry of the supersonic propagation of the ablation front in condensed matter that was pushed sideways by a conical shock wave. Small-scale ?lamentation of the laser beam caused by thermal self-focusing of radiation in the crater-con?ned plasma was evidenced by the presence of a microcrater relief on the bottom of the main crater. In translucent PMMA, with a penetration depth for UV light of several hundred micrometers, a long narrow channel of length 1 mm and diameter 30 μm was observed emerging from the crater vertex. Similar channels with a length-to-diameter aspect ratio of ～1000 were produced by a repeated-pulse KrF laser in PMMA and fused silica glass at an intensity of ～109 W cm?2. This channel formation is attributed to the effects of radiation self-focusing in the plasma and Kerr self-focusing in a partially transparent target material after shallow-angle re?ection by the crater wall. Experimental modeling of the initial stage of inertial con?nement fusion-scale direct-drive KrF laser interaction with subcritical coronal plasmas from spherical and cone-type targets using crater-con?ned plasmas seems to be feasible with increased laser intensity above 1014 W cm?2.
关键词： fused silica glass,UV radiation,PMMA,KrF laser,plasma,ICF,self-focusing
更新于2025-09-23 15:21:01
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A Soft X-Ray Radiation Source Formed in Supersonic Argon Gas Jets under the Action of High-Contrast Femtosecond Laser Pulses of Relativistic Intensity
摘要： The possibility of designing a compact source of soft X-ray radiation without the accompanying generation of fast electrons is under study. The source is formed by the interaction of high-contrast femtosecond laser pulses of relativistic intensity with supersonic argon gas jets. The optimal conditions are found under which the conversion coefficient to soft X-ray radiation in the range of 2.9–3.3 keV reaches 8.57 × 10–5.
关键词： X-ray radiation,gas target,laser plasma
更新于2025-09-23 15:21:01
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Laser-generated plasmas in length scales relevant for thin film growth and processing: simulation and experiment
摘要： In pulsed laser deposition, thin film growth is mediated by a laser-generated plasma, whose properties are critical for controlling the film microstructure. The advent of 2D materials has renewed the interest in how this ablation plasma can be used to manipulate the growth and processing of atomically thin systems. For such purpose, a quantitative understanding of the density, charge state, and kinetic energy of plasma constituents is needed at the location where they contribute to materials processes. Here, we study laser-induced plasmas over expansion distances of several centimeters from the ablation target, which is the relevant length scale for materials growth and modification. The study is enabled by a fast implementation of a laser ablation/plasma expansion model using an adaptive Cartesian mesh solver. Simulation outcomes for KrF excimer laser ablation of Cu are compared with Langmuir probe and optical emission spectroscopy measurements. Simulation predictions for the plasma-shielding threshold, the ionization state of species in the plasma, and the kinetic energy of ions, are in good correspondence with experimental data. For laser fluences of 1–4 J cm?2, the plume is dominated by Cu0, with small concentrations of Cu+ and electrons at the expansion front. Higher laser fluences (e.g. 7 J cm?2) lead to a Cu+ -rich plasma, with a fully ionized leading edge where Cu2+ is the dominant species. In both regimes, simulations indicate the presence of a low-density, high-temperature plasma expansion front with a high degree of ionization that may play a significant role in doping, annealing, and kinetically-driven phase transformations in 2D materials.
关键词： pulsed laser deposition,plasma diagnostics,plasma processing of 2D materials,laser plasma simulation,2D materials,laser ablation,plasma assisted processing
更新于2025-09-23 15:19:57
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Direct laser acceleration of electrons in high-Z gas target and effect of threshold plasma density on electron beam generation
摘要： An experimental study of laser driven electron acceleration in N2 and N2-He mixed gas-jet target using laser pulses of duration ~60-70 fs is presented. Generation of relativistic electron beam with quasi-thermal spectra was observed at a threshold density of ~1.6×1018 cm-3 in case of the pure N2. At an optimum fraction of 50% of He in N2, generation of quasi-monoenergetic electron beams was observed at a comparatively higher threshold density of ~2×1018 cm-3, with an average peak energy of ~168 MeV, average energy spread of ~21%, and average total beam charge of ~220 pC. Electron acceleration could be attributed to the direct laser acceleration as well as the hybrid mechanism. Observation of an optimum fraction of He in N2 (in turn threshold plasma density) for comparatively better quality electron beam generation could be understood in terms of the plasma density dependent variation in the dephasing rate of electrons with respect to the transverse oscillating laser field. Results are also supported by the 2D PIC simulations performed using the code EPOCH.
关键词： Laser Wakefield Acceleration,Laser Plasma Acceleration,Direct Laser Acceleration,Ionization Induced Injection
更新于2025-09-23 15:19:57