Plasma Expansion Dynamics Research Articles

Spectral behavior and expansion dynamics of Gd plasma generated by dual-pulse laser irradiation

Laser-produced gadolinium plasma (Gd-LPP) emerges as a promising candidate for next-generation nanolithography light sources. In this study, a dual laser pulse scheme was implemented to achieve a narrow spectral peak. By varying the pre-main pulse delay and pre-pulse laser energy, optimal conditions of 40 ns delay and 50 mJ energy were identified to improve spectral purity. Radiation hydrodynamics simulations revealed that the improved spectral purity stems from a flatter density gradient at the ablation front and a lower average electron density in the EUV emission region. Additionally, reheating the pre-formed plasma with a short main pulse mitigated plasma squeezing, resulting in an even lower electron density and thus improved spectral purity. Our findings suggest that spectral narrowing in the dual-pulse scheme, essential for better matching with multilayer reflection bandwidths, can be optimized through precise control of pre-pulse energy, pre-main delay, and main-pulse duration.

Dynamics of spatially confined ns laser induced atmospheric air plasma and shock waves: visualization vis-à-vis validation

A clear visualization of the physical processes of spatially confined ns laser induced atmospheric air plasma within a rectangular glass cavity using optical imaging is presented. The occurrence of various processes starting from the early plasma and shock wave expansion dynamics to shock reflection at the cavity boundaries and compression of the plasma due to reflected shockwaves is studied using defocused shadowgraphy and self-emission imaging techniques. Experimentally, we evidenced that the counter propagating reflected primary shockwaves interact with the expanding plasma generating a secondary shockwave which compresses the plasma core, modifying the plasma morphology resulting in enhanced plasma parameters. The numerical simulations performed via the two-dimensional hydrodynamic (2D-HD) FLASH codes, revealed that the number density increases up to a maximum of 3.6 times compared to the unconfined plasma. The input laser pulse energy and the aspect ratio of the cavity is observed to play a dominant role in the confinement and compression of the plasma.

Precision Tests of the Nonlinear Mode Coupling of Anisotropic Flow via High-Energy Collisions of Isobars

Valuable information on dynamics of expanding fluids can be inferred from the response of such systems to perturbations in their initial geometry. We apply this technique in high-energy 96Ru+96Ru and 96Zr+96Zr collisions to scrutinize the expansion dynamics of the quark-gluon plasma, where the initial geometry perturbations are sourced by the differences in deformations and radial profiles between 96Ru and 96Zr, and the collective response is captured by the change in anisotropic flow Vn between the two collision systems. Using a transport model, we analyze how the nonlinear coupling between lower-order flow harmonics V 2 and V 3 to the higher-order flow harmonics V 4 and V 5, expected to scale as and V 5NL = χ 5 V 2 V 3, gets modified as one moves from 96Ru+96Ru to 96Zr+96Zr systems. We find that these scaling relations are valid to high precision: variations of order 20% in V 4NL and V 5NL due to differences in quadrupole deformation, octupole deformation, and nuclear skin modify χ 4 and χ 5 by about 1–2%. Percent-level deviations are however larger than the expected experimental uncertainties and could be measured. Therefore, collisions of isobars with different nuclear structures are a unique tool to isolate subtle nonlinear effects in the expansion of the quark-gluon plasma that would be otherwise impossible to access in a single collision system.

Off-harmonic optical probing of high intensity laser plasma expansion dynamics in solid density hydrogen jets

Due to the non-linear nature of relativistic laser induced plasma processes, the development of laser-plasma accelerators requires precise numerical modeling. Especially high intensity laser-solid interactions are sensitive to the temporal laser rising edge and the predictive capability of simulations suffers from incomplete information on the plasma state at the onset of the relativistic interaction. Experimental diagnostics utilizing ultra-fast optical backlighters can help to ease this challenge by providing temporally resolved inside into the plasma density evolution. We present the successful implementation of an off-harmonic optical probe laser setup to investigate the interaction of a high-intensity laser at 5.4times 10^{21},hbox {W/cm}^{2} peak intensity with a solid-density cylindrical cryogenic hydrogen jet target of {5},{upmu }mathrm{m} diameter as a target test bed. The temporal synchronization of pump and probe laser, spectral filtering and spectrally resolved data of the parasitic plasma self-emission are discussed. The probing technique mitigates detector saturation by self-emission and allowed to record a temporal scan of shadowgraphy data revealing details of the target ionization and expansion dynamics that were so far not accessible for the given laser intensity. Plasma expansion speeds of up to (2.3 pm 0.4)times 10^{7},hbox {m/s} followed by full target transparency at {1.4},{mathrm{ps}} after the high intensity laser peak are observed. A three dimensional particle-in-cell simulation initiated with the diagnosed target pre-expansion at {-0.2},{mathrm{ps}} and post processed by ray tracing simulations supports the experimental observations and demonstrates the capability of time resolved optical diagnostics to provide quantitative input and feedback to the numerical treatment within the time frame of the relativistic laser-plasma interaction.

Time-Resolved Imaging of Femtosecond Laser-Induced Plasma Expansion in a Nitrogen Microjet

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an intensified charge-coupled device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on a fused silica substrate by femtosecond laser micromachining. This technique enabled high accuracy and three-dimensional capabilities, thus, providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy.

Research on the triggering process of a laser-triggered vacuum switch

The laser-triggered vacuum switch (LTVS) is a type of high-voltage closing switch with broad application prospects in pulsed-power technology. Research into the triggering process of the LTVS is not only helpful to understand the triggering mechanism of the LTVS but also beneficial to the optimization of the LTVS. In this paper, the triggering process and the delay time of a LTVS with a Ti–KCl mixture target was analyzed theoretically. A numerical simulation was performed to describe the laser-target ablation process and the expansion dynamics of the initial plasma. The simulation results were compared with the experimental results. It is clear that the triggering process and delay time strongly depend on the laser intensity. As the laser intensity rises, the velocity of initial plasma increases, resulting in a shorter delay time of the LTVS. Increasing the gap voltage can also shorten the delay time.

Laser induced dielectric breakdown in reactive mixture SiF4 + H2

Important chemical process of reduction of SiF4 by hydrogen is realized in laser induced dielectric breakdown (LIDB) plasma in a gas mixture of SiF4 and H2. The process may be an alternative to a method of plasma enhanced chemical vapor deposition (PECVD) which is commonly used for production of pure and isotopically pure silicon films. The composition of laser induced plasma in gases SiF4, SiF4 + H2, SiF4 + H2 + Ar at atmospheric pressure is studied and compared to the composition of inductively coupled plasma (ICP) in the same gases but at reduced pressure of 3 Torr. The gaseous products of chemical reactions are inferred from optical emission spectroscopy (OES) and IR spectroscopy. The reaction products of silicon fluoride SiF and fluorosilanes SiHxFy (x, y = 1, 2, 3) in LIDB plasma are observed and confirmed by equilibrium chemistry calculations and simulations of plasma expansion dynamics using a fluid dynamic-chemical plasma model. It is further suggested that chemisorption of fluorinated species like SiFx (x = 1, 2) followed by the surface reaction with H-atoms lead to a formation of silicon-to‑silicon bonds on a substrate surface. A conclusion is drawn that energetic laser induced plasma can prove efficient for one-step PECVD by hydrogen reduction of SiF4.

The effect of inter-pulse delay on the spectral emission and expansion dynamics of plasma in dual-pulse fiber-optic laser-induced breakdown spectroscopy

The role of inter-pulse delay on plasma dynamics and spectral emission in dual-pulse fiber-delivery plasma has been investigated using fast imaging, optical emission spectroscopy, and laser shadowgraphy. The detection on the return spectrum in dual-pulse fiber-optic laser-induced breakdown spectroscopy showed that the self-reversal and self-absorption were reduced as the inter-pulse delay increased from 50 to 1000 ns. Using scanning electron microscopy, the ablation depth showed a changing trend of increasing first and then decreasing, and a maximum of ∼2.8 μm was achieved at 250-ns inter-pulse delay. Experimental results confirmed that the improvement was due to the reduction of the plasma thickness from 1.161 mm to 0.964 mm, and the calculation of electronic excitation temperature along the photon collection path showed that the excited atom densities became more spread, which both contributed to the self-absorption reduction. At a long inter-pulse delay, the plasma trailing edge would gradually separate from the target surface with a little further expansion distance of the leading edge, resulting in the reduction of plasma thickness after a time delay of several hundred nanoseconds. The heating of the peripheral cold particles by the second-generation plasma in the later expansion led to the rapid reduction of the peak temperature. Also, the early expansion trajectory of the second-generation plasma was tracked by laser shadowgraphy, which started to appear at an inter-pulse delay of 100 ns, and the average expansion velocity reached its maximum of ∼3.8 km/s.

Experimental Study of Space Charge Structure and Expansion Dynamics of Laser Ablation Plasma

Using the method of spectrally selective photorecording in a nanosecond temporal resolution, the distribution of neutral atoms and single- and double-charged gallium ions in a plasma plume is investigated under the conditions of laser ablation of a gallium-indium target and so is the expansion dynamics of both components and the plume as a whole. The expansion velocity of a neutral atomic component of the plume is found. The expansion velocity of the glow boundary and the shift velocity of the glow intensity maximum are found to be close to 8.5∙103 and 6∙103 m/s, respectively. The kinetic energy range, corresponding to these values for the gallium atoms (13–26 eV) is quite consistent with the position of local maximum measured earlier from the energy distribution of single-charged gallium ions.

Экспериментальное исследование пространственно-зарядовой структуры и динамики разлета сгустка плазмы лазерной абляции

Экспериментальное исследование пространственно-зарядовой структуры и динамики разлета сгустка плазмы лазерной абляции

Plasma expansion accompanying superthermal electrons in over-picosecond relativistic laser-foil interactions

We study the plasma expansion dynamics in over-picosecond relativistic laser-foil interactions using one-dimensional particle-in-cell (PIC) simulations. A new expansion mode ‘isofield expansion’ appears after the well-known isothermal expansion due to the continuous energy input from the laser light to the plasma. The blowout of the heated plasma at the front surface triggers the transition from the isothermal mode to the new mode. In the new expansion mode, electrons and ions expand quasi-neutrally with a constant sheath electric field, and a large scale low density plasma is formed where superthermal electrons are produced efficiently. A two-dimensional PIC simulation confirms the appearance of the isofield expansion mode after the plasma blowout for a large focal spot laser.

Influence of distance between sample surface and focal point on the expansion dynamics of laser-induced silicon plasma under different sample temperatures in air

In this paper, we explored the influence of distance between sample surface and focal point on the expansion dynamics of laser-induced plasma under different sample temperatures in air. A Nd:YAG nanosecond pulse laser was used to ablate silicon and produce plasma plume. Using fast photography technology, we captured the images of the plasma plumes at different focusing positions and sample temperatures. During the expansion of plasma plume, with the decrease of the distance between focal point and sample surface, the emission intensity of the plasma increased first, and then dropped. In addition, the increase in the sample temperature could improve the expansion velocity of the plasma plume. Moreover, higher laser energy and sample temperatures could enhance the emission intensity and increase the plasma lifetime.

Effect of laser beam size on the dynamics of ultrashort laser-produced aluminum plasma in vacuum

In laser-produced plasma experiments, the diameter of the irradiating laser beam on the target surface is a major parameter that influences the ablation mechanisms, plasma emission intensity, charged particle ejection, and plume morphology. In this work, the expansion dynamics of an ultrashort laser-produced aluminum plasma is investigated as a function of the laser beam size on the target, using a combination of diagnostic tools, viz., optical emission spectroscopy, fast gated time-resolved imaging, and ion current measurements. A Ti:sapphire laser delivering 100 fs, 6 mJ pulses at 800 nm is used for producing plasma from a pure Al target placed in vacuum (10−5 Torr) at different positions with respect to the geometrical focus of the beam. Optical emission spectroscopic analysis of the plasma shows that higher emission intensities and ion populations are obtained for smaller beam sizes. Time-resolved Intensified Charge Coupled Device (ICCD) imaging of the expanding plasma shows a spherical morphology for plumes produced by smaller beam sizes and a cylindrical morphology for those produced by larger beam sizes. Temporal profiles of ion emission measured using a Faraday cup are in agreement with ICCD data, featuring a dual peak structure for larger beam sizes indicating distinct slow and fast ionic species, arising from changes in the ablation mechanism for varying laser fluences. Plume expansion is modelled by free expansion for the fast species and by shock wave propagation for the slow species. Ion flux and velocities are relatively high for smaller beam sizes. These studies can be of potential importance for laser processing applications, including laser welding, drilling, and micromachining.

Investigation of laser-induced plasma at varying pressure and laser focusing

Expansion dynamics of laser-induced plasma is studied for different focal positions of the ablation laser in the pressure range 10-2 - 105 Pa of the ambient air. The experimental results indicate that both the parameters significantly affect the plasma size, shape, intensity, reproducibility, and distance from the target surface. At pressures above 10 Pa, the plasma plume is confined by the ambient gas; the plumes are more compact and travel shorter distances from the target as compared to the analogous plume characteristics at pressures below 10 Pa. The pulse-to-pulse reproducibility of the integral emission intensity of the plasma is also different for different focal positions and pressures. It is found that the focal positions -1 cm and -2 cm below the target surface yield the most reproducible and intense emission signals as measured at the 600 ns delay time with the 100 ns gate. The information obtained can be of importance for pulsed laser deposition, laser welding, and analytical spectroscopy at reduced pressures. In general, a correct choice of the focal position and pressure of an ambient gas is very important for obtaining the strongest plasma emission, good reproducibility, and desired plasma plume shape.

Plasma Expansion Dynamics in Hydrogen Gas

Micro-plasma is generated in ultra-high-pure hydrogen gas, which fills the inside of a cell at a pressure of (1.08 ± 0.033) × 105 Pa by using a Q-switched neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser device operated at a fundamental wavelength of 1064 nm and a pulse duration of 14 ns. The micro-plasma emission spectra of the hydrogen Balmer alpha line, Hα, are recorded with a Czerny–Turner type spectrometer and an intensified charge-coupled device. The spectra are calibrated for wavelength and corrected for detector sensitivity. During the first few tens of nanoseconds after the initiation of optical breakdown, the significant Stark-broadened and Stark-shifted Hα lines mark the well-above hypersonic outward expansion. The vertical diameters of the spectrally resolved plasma images are measured for the determination of expansion speeds, which were found to decrease from 100 to 10 km/s for time delays of 10 to 35 ns. For time delays of 0.5 µs to 1 µs, the expansion speed of the plasma decreases to the speed of sound of 1.3 km/s in the near ambient temperature and pressure of the hydrogen gas.

Investigation of the expansion dynamics of silicon plasmas generated by double nanosecond laser pulses

A systematic investigation of the expansion dynamics of plasma plumes generated by two Q-switched Nd:YAG lasers at 1064 nm wavelength operating on a silicon target was undertaken for the inter-pulse delay times of 0, 100, 200, and 400 ns using a technique involving fast-gated intensified charge-coupled device imaging. Our results indicate that the plasmas exhibit free expansion in a vacuum environment at an inter-pulse delay time of 0 ns. With increasing inter-pulse delay time, the plasma front becomes sharpened and an interaction boundary is formed. Moreover, using the radiation intensity distribution along the plasma axis of symmetry, the formation and evolution mechanism of the plasmas generated by the double pulses was analyzed at different inter-pulse delay times. Finally, the experimental results of the expansion of the plasma core and front were compared with a radiation hydrodynamics model and a drag model, and were found to be generally in good agreement.

Internal mixing dynamics of Cu/Sn-Pb plasmas produced by femtosecond laser ablation

Chemical imaging applications using Laser Induced Breakdown Spectroscopy (LIBS) involve laser ablation sampling at interfaces or boundaries between materials with different thermophysical and optical properties, leading to the formation of two initially isolated plasmas. The mechanisms of mixing in these plasmas and their direct implications on spectral emission and chemical imaging remain largely unknown. We investigate the mixing dynamics of isolated plasmas produced using femtosecond (fs) laser pulses at the interface between two different model Cu and SnPb samples. Specifically, we study the spatial and temporal mixing dynamics and outer plasma expansion dynamics of the fs plasma components. The time-resolved degree of component mixing, horizontal and vertical expansion, mixing speed, and temperature and electron density of the heterogeneous plasma are characterized. Mixing processes are initiated early on, <100 ns after the laser pulse, and continue taking place until the end of plasma emission persistence at a constant velocity of 104 cm/s. These findings demonstrate that proper selection of detection timing parameters and signal collection position are critically important in precise LIBS measurements to ensure that full plasma mixing has taken place and that homogeneous spectral emission is properly detected.

Laser-induced plasma imaging for low-pressure detection.

A novel technique based on laser induced plasma imaging is proposed to measure residual pressure in sealed containers with transparent walls, e.g. high voltage vacuum interrupter in this paper. The images of plasma plumes induced on a copper target at pressure of ambient air between 10-2Pa and 105Pa were acquired at delay times of 200ns, 400ns, 600ns and 800ns. All the plasma images at specific pressures and delay times showed a good repeatability. It was found that ambient gas pressure significantly affects plasma shape, plasma integral intensities and expansion dynamics. A subsection characteristic method was proposed to extract pressure values from plasma images. The method employed three metrics for identification of high, intermediate and low pressures: the distance between the target and plume center, the integral intensity of the plume, and the lateral size of the plume, correspondingly. The accuracy of the method was estimated to be within 15% of nominal values in the entire pressure range between 10-2Pa and 105Pa. The pressure values can be easily extracted from plasma images in the whole pressure range, thus making laser induced plasma imaging a promising technique for gauge-free pressure detection.

Influence of the distance between target surface and focal point on the expansion dynamics of a laser-induced silicon plasma with spatial confinement

Expansion dynamics of a laser-induced plasma plume, with spatial confinement, for various distances between the target surface and focal point were studied by the fast photography technique. A silicon wafer was ablated to induce the plasma with a Nd:YAG laser in an atmospheric environment. The expansion dynamics of the plasma plume depended on the distance between the target surface and focal point. In addition, spatially confined time-resolved images showed the different structures of the plasma plumes at different distances between the target surface and focal point. By analyzing the plume images, the optimal distance for emission enhancement was found to be approximately 6mm away from the geometrical focus using a 10cm focal length lens. This optimized distance resulted in the strongest compression ratio of the plasma plume by the reflected shock wave. Furthermore, the duration of the interaction between the reflected shock wave and the plasma plume was also prolonged.

TOKES simulations to compare gas and pellet injection for disruption mitigation in ITER

Disruption mitigation by shattered Ne pellet injection (SPI) has been simulated for an H-mode ITER D-T discharge of 280 MJ stored energy using the 3D TOKES code. Heating of the first wall from the radiation flash during the thermal quench of the disruption initiated by the injected pellets has been assessed. The dynamics of Ne plasma expansion in the core with radiation from this plasma have been simulated for the series of pellet sizes from 5.4 × 1024 to 8.6 × 1022 Ne atoms. The threshold pellet size for irradiation of the core energy has been found. The results of SPI and massive gas injection simulations are compared.