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Effects of background gases and pressure in pulsed laser deposition of Al-doped ZnO
摘要： Background gases (O2, He or Ar) with the pressure from ~ 10?3 Pa to 133.3 Pa are used in 355 nm laser deposition of Al-doped ZnO at room temperature. The effects of these gases and pressure on plasma formation are studied by optical emission spectroscopy (OES) and time of flight (TOF) measurement. The OES results show that the emission intensity of the species in O2 and Ar decrease slightly and then increase exponentially above ~ 5 Pa. The emission intensity in Ar is the highest, followed by emission in O2 whilst the emission in He is low and weakly depend on background gas pressure. TOF measurements indicate that the ion velocity decrease with increasing O2 and Ar pressure at about 5–10 Pa. The ion velocity is highest in He while the ion velocities in O2 and Ar are similar. Thin-film samples deposited in different gas at 2.6 Pa are amorphous, but those deposited at 133.3 Pa are crystalline and exhibit different morphologies and optical properties depending on type of gas. Samples deposited in O2 are highly transparent but those deposited in He and Ar contain nano and micron-sized structures with <50% transmittance. In addition, Zn crystallites are detected by X-ray diffraction.
关键词： Pulsed laser deposition,Background gases,Aluminum-doped zinc oxide,Pressure,Laser produced plasma,Nanostructured films
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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Terahertz plasma wave localization and velocity control in tapered double-layer graphene heterostructure
摘要： Terahertz plasma wave (plasmon) localization and velocity control in tapered heterostructure (taper) with double-layer graphene were numerically studied. We employ a simple rigorous theoretical model to find out the plasmon localization length and energy velocity values along the tapered structure. It is shown that the plasmon decelerates while moving from the taper apex and the deceleration process is accompanied with increase of the plasmon wave localization. While moving along the structure from the taper apex, the plasmon energy velocity as well as the plasmon localization length can become nearly an order of magnitude smaller as compared to the values near the taper apex.
关键词： plasmon localization,Terahertz plasma wave,tapered heterostructure,velocity control,double-layer graphene
更新于2025-09-23 15:21:01
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Control of current waveform of laser ion source using pulsed magnetic field
摘要： We investigated plasma behavior with a solenoid-generated static and pulsed magnetic field by measuring time evolution in a transverse ion current profile to control the ion current waveform of a laser ion source. The results showed that static magnetic fields cannot enhance the ion current in the slow region of time of flight (TOF). However, a pulsed magnetic field whose magnetic flux density is rising while a plasma passes through the solenoid can enhance the ion current in the same TOF region. The results showed that applying a pulsed magnetic field to a laser-produced plasma is an effective way to control an ion current waveform in a laser ion source to produce an ion beam with a flat-top-shaped pulse. By using a pulsed magnetic field, the ion current waveform peak was held for ～50 μs.
关键词： laser ion source,ion current waveform,pulsed magnetic field,plasma behavior
更新于2025-09-23 15:21:01
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Laser-produced plasmas as drivers of laboratory collisionless quasi-parallel shocks
摘要： The creation of a repeatable collisionless quasi-parallel shock in the laboratory would provide a valuable platform for experimental studies of space and astrophysical shocks. However, conducting such an experiment presents substantial challenges. Scaling the results of hybrid simulations of quasi-parallel shock formation to the laboratory highlights the experimentally demanding combination of dense, fast, and magnetized background and driver plasmas required. One possible driver for such experiments is high-energy laser-produced plasmas (LPPs). Preliminary experiments at the University of California, Los Angeles, have explored LPPs as drivers of quasi-parallel shocks by combining the Phoenix Laser Laboratory [Niemann et al., J. Instrum. 7, P03010 (2012)] with a large plasma device [Gekelman et al., Rev. Sci. Instrum. 87, 025105 (2016)]. Beam instabilities and waves characteristic of the early stages of shock formation are observed, but spatial dispersion of the laser-produced plasma prematurely terminates the process. This result is illustrated by experimental measurements and Monte Carlo calculations of LPP density dispersion. The experimentally validated Monte Carlo model is then applied to evaluate several possible approaches to mitigating LPP dispersion in future experiments.
关键词： beam instabilities,collisionless quasi-parallel shocks,plasma dispersion,laser-produced plasmas,Monte Carlo calculations
更新于2025-09-23 15:21:01
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Biocompatible nanoparticles production by pulsed laser ablation in liquids
摘要： The preparation of spherical metallic nanoparticles (NPs), in the range of 10–100 nm, using pulsed laser ablation in water has particular interest in many scienti?c ?elds. The fast released laser energy to the solid metal in water produces plasma at the solid-liquid interface generating NPs in solution. The size distribution and the solution concentration depend by many parameters concerning the laser source (wavelength, pulse energy, pulse duration), the irradiation conditions (target depth in water, focal spot, repetition rate, irradiation time), and the medium where the ablation occurs (water, solution concentration, presence of surfactants). Optimal conditions can be found to control the average particle size, the size distribution, and the coalescence e?ect. A study of the NPs dependence from the ns pulsed Nd:YAG laser, irradiating metals in water is presented, discussing also the physical characterization of the produced NPs employing microscopy and optical analyses.
关键词： Plasma generation (laser-produced, RF, x ray-produced),Lasers
更新于2025-09-23 15:21:01
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Dispersion characteristics of terahertz transverse electric mode in a smooth-wall cylindrical waveguide with a degenerate plasma layer
摘要： The propagation of transverse electric mode in a cylindrical metallic smooth-wall waveguide contains a dielectric rod and a cold collisionless unmagnetized degenerate plasma layer is analytically investigated in the terahertz frequency region. The dispersion relations of fast and slow waves for this mode are derived and solved numerically. The effects of geometrical and physical parameters such as dielectric, plasma and metal radii, and dielectric permittivity on the dispersion characteristics of terahertz transverse electric mode and its frequency spectrum are studied. It is shown that the decrease of dielectric permittivity and metal radius, and the increase of degenerate plasma radius leads to higher frequency fast waves. It is also indicated that an increase in the dielectric radius results in a decrease in the frequency of fast waves. In addition, it is found that by reducing the dielectric rod radius and with increasing metal radius, the frequency is increased in the slow waves. Finally, it is shown that the increase in dielectric permittivity causes a decrease in the frequency of both fast and slow waves.
关键词： Dielectric layer,Waveguide,Group velocity,Unmagnetized degenerate plasma,Dispersion relation
更新于2025-09-23 15:21:01
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Detection of Nutrition and Toxic Elements in Pakistani Pepper Powders Using Laser Induced Breakdown Spectroscopy
摘要： In the current paper, we applied laser induced breakdown spectroscopy (LIBS) to determine the elemental distribution of nutritional and trace heavy metals in pepper powders available in Pakistan using standard calibration curve laser induced breakdown spectroscopy (CC-LIBS) technique. The samples were found to contained elements like K, Ca, Mg, Na, Fe, Zn, Al, Pb, Cu, and Cr. Additionally, we also identified the atmospheric H-alpha line of hydrogen in the spectra which was used to estimate the electron number density. To achieve a highly sensitive LIBS system to determine nutritional and trace amounts of toxic metals in pepper powders and to achieve the best limit of detection, the LIBS system was optimized by studying the dependency of LIBS signal intensity on laser irradiance, variation in spacing between the focusing lens and target as well on the gate width. To justify the results of LIBS study, we also determined the concentration of alike (duplicate) peppers by digesting samples in appropriate solvents using a standard method like inductively coupled plasma-optical emission spectrometry (ICP-OES). The minimum detection limit was recognized for trace heavy metals from calibration curves. The results of LIBS displayed noteworthy conformity with those acquired from the ICP-OES analysis. Results of both the techniques clearly revealed that K was the most abundant element in all the peppers followed by Ca, Mg, Na, Fe, Al, Pb, Zn, Cu, and Cr. The relative accuracy of our LIBS system for different species as compared with ICP technique was in the range of 0.08–0.3 at 2.5 % error confidence. Conclusively, the present work demonstrated the suitability of LIBS technique due to its rapid, non destructive and eco-friendly approach for food security.
关键词： ICP-OES,detection of heavy metals,peppers analysis,laser induced breakdown spectroscopy,plasma parameters,Health impacts of toxic metals,laser applications
更新于2025-09-23 15:21:01
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Comparison of quantitative analyses using SIMS, atom probe tomography, and femtosecond laser ablation inductively coupled plasma mass spectrometry with Si <sub/>1a??X</sub> Ge <sub/>X</sub> and Fe <sub/>1a??X</sub> Ni <sub/>X</sub> binary alloys
摘要： Due to their electrical and physical properties, Si1?XGeX materials are widely used in microelectronic devices. In particular, the Ge component found within Si1?XGeX compounds is important for enhancing carrier mobility and altering the lattice constant of metal-oxide-semiconductor field-effect transistors. In this study, magnetic sector secondary ion mass spectrometry (magnetic sector SIMS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to determine the accurate concentrations of major compositions present within binary alloy samples. However, quantitative SIMS analysis is limited by the matrix effect, which influences the sputter yield of an element in a compound and alters the secondary ionization yields. Quantitative deviations that were due to the matrix effect were reduced by using Cs cluster ions (MCs+ and MCs2+) instead of elemental ions; the SIMS results using the elements were, therefore, compared with those using MCs+ and MCs2+ cluster ions. In the case of Fe1?XNiX alloys that have a less matrix effect compared to Si1?XGeX alloys, both the Cs primary ion beam (Cs+) and an oxygen primary ion beam (O2+) were used to measure the Fe1?XNiX compositions. The quantitative results from the two different primary ion beams were then compared to understand the ionization process. Deviations in the quantitative values gained with the O2+ beam were lower than those obtained using the Cs+ primary ions, meaning that using oxygen as the primary ion improves the accuracy in quantifying Fe1?XNiX compounds. Other reliable tools for analysis such as atom probe tomography and femtosecond laser ablation inductively coupled plasma mass spectrometry were also used in the quantitative analysis, with results that were consistent with the most accurate results obtained using magnetic sector SIMS and ToF-SIMS.
关键词： Si1?XGeX,femtosecond laser ablation inductively coupled plasma mass spectrometry,atom probe tomography,SIMS,Fe1?XNiX,binary alloys
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