Plume Expansion Dynamics Research Articles

Double layer acceleration of ions with differently charged states in a laser induced plasma

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations.

Ion expansion dynamics of laser induced multi-elemental plasmas

Ablation of multi-elemental materials by nanosecond lasers is often used to deposit oxide thin films. Understanding the ablation plume dynamics is of utmost importance to gain a detailed insight into thin film growth of materials with a complex composition. In this study, the plume expansion dynamics of several compound materials (AuCu, La0.33Ca0.67MnO3, and LiMn2O4) were characterized by measuring the angular-dependent kinetic energy (KE) distributions of ionic plasma species produced by KrF- and XeCl-excimer laser ablation in vacuum. The distributions of the lightest plume ions were found to differ fundamentally from those of other ions. The latter are similar to the energy distributions observed in single-component plumes and represent a low-energy peak and high-energy tail, while those for the lightest ions consist of at least two distinct peaks. These observations can be explained by assuming the formation of a dynamic double layer (DL) at the front of the plasma giving rise to different acceleration rates for light and heavier ions. As a consequence, heavier elements stay longer within the dynamic DL and gain larger KEs that leads to the observed ion separation. Extending these considerations into three dimensions yields an anisotropic acceleration concept for the plasma ions with high acceleration rates and longer presence within the DL normal to the target surface and lower acceleration rates and shorter time in the parallel direction.

Effect of evaporation-flux nonuniformity along the irradiation-spot radius on the plume expansion dynamics during pulsed laser ablation in vacuum

Effect of evaporation-flux nonuniformity along the irradiation-spot radius on the plume expansion dynamics during pulsed laser ablation in vacuum

Doppler splitting and expansion dynamics of laser-produced plasma plume under a high vacuum ambience

Doppler splitting appeared after the plume front passed because of the formation of the contact layer and quasi-cavity in the plasma plume and the movement of atoms in the lateral direction at a high vacuum.

On the expansion dynamics of plasma plume produced by laser ablation of LiYF4 crystal in a helium atmosphere

The effect of helium ambient gas on the expansion dynamics of plasma plume produced by ablating the LiYF4 crystal with 355 nm laser pulses is investigated. To study the expansion dynamics, the time-resolved optical signals from the plume constituents, either neutral or ionized, were recorded as a function of various experimental parameters, including laser fluency, at different distances, d, from the target along the expansion direction of the plume and at various angles with reference to the target normal. The analysis of the plume constituents at different distances from the target was used to derive the expansion velocities of the species. Depending on the species and on d, the shifted Maxwell–Boltzmann distribution component of the fit gave the values of the expansion velocities in the range 1.0 × 104 m s−1–4.0 × 104 m s−1. The effect of laser fluency on the expansion velocities of the plume species was also investigated. With the exception of Y and Y+, the expansion velocities of all the plume species, increased linearly with increasing laser fluency up to ∼8 J cm−2. Beyond this value, a saturation regime is observed. The angular distribution of the plume constituents in 1 Pa of He evidenced that all the plume species were focused along the target normal, and the FWHM of the angular distribution curve resulted reduced when compared with the vacuum.

Energy and flux measurements of laser-induced silver plasma ions by using Faraday cup

Silver (Ag) plasma has been generated by employing Nd:YAG laser (532 nm, 6 ns) laser irradiation. The energy and flux of ions have been evaluated by using Faraday cup (FC) using time of flight (TOF) measurements. The dual peak signals of fast and slow Ag plasma ions have been identified. Both energy and flux of fast and slow ions tend to increase with increasing irradiance from 7 GW cm−2 to 17.9 GW cm−2 at all distances of FC from the target surface. Similarly a decreasing trend of energies and flux of ions has been observed with increasing distance of FC from the target. The maximum value of flux of the fast component is 21.2 × 1010 cm−2, whereas for slow ions the maximum energy and flux values are 8.8 keV, 8.2 × 1012 cm−2 respectively. For the analysis of plume expansion dynamics, the angular distribution of ion flux measurement has also been performed. The overall analysis of both spatial and angular distributions of Ag ions revealed that the maximum flux of Ag plasma ions has been observed at an optimal angle of ∼15°. In order to confirm the ion acceleration by ambipolar field, the self-generated electric field (SGEF) measurements have also been performed by electric probe; these SGEF measurements tend to increase by increasing laser irradiance. The maximum value of 232 V m−1 has been obtained at a maximum laser irradiance of 17.9 GW cm−2.

Infrared MALDI Mass Spectrometry with Laser-Induced Postionization for Imaging of Bacterial Colonies.

Ultraviolet matrix-assisted laser desorption ionization mass spectrometry imaging (UV-MALDI-MSI) is a powerful tool to visualize bacterial metabolites in microbial colonies and in biofilms. However, a challenge for the method is the efficient extraction of analytes from deeper within the bacterial colonies and from the cytoplasm of individual cells during the matrix coating step. Here, we used a pulsed infrared (IR) laser of 2.94 μm wavelength to disrupt and ablate bacterial cells without a prior coating with a MALDI matrix. Instead, tissue water or, in some experiments, in addition a small amount of glycerol was exploited for the deposition of the IR laser energy and for supporting the ionization of the analytes. Compared to water, glycerol exhibits a lower vapor pressure, which prolonged the available measurement time window within an MSI experiment. Mass spectra were acquired with a hybrid Synapt G2-S HDMS instrument at a pixel size of 120 μm. A frequency-quadrupled q-switched Nd:YAG laser with 266 nm wavelength served for laser-induced postionization (MALDI-2). In this way, the ion abundances of numerous small molecules such as nucleobases, 2-alkyl-quinolones, a prominent class of Pseudomonas aeruginosa signaling molecules involved in one of the three quorum-sensing pathways, and also the signals of various bacterial phospholipids were boosted, partially by orders of magnitude. We analyzed single and cocultured colonies of Gram-negative P. aeruginosa and of Gram-positive Bacillus subtilis and Staphylococcus aureus as exemplary bacterial systems. To enable a rapid (within 5 s) MSI-compatible steam inactivation in a custom-made autoclave filled with hot water steam, bacterial cultures were grown on porous polyamide membranes. Compared to a UV-MALDI-2-MS measurement of the same systems, mass spectra with a reduced low mass background were generally generated. This resulted in the unequivocal detection of numerous metabolites only with the IR laser. In a fundamental part of our study, and to optimize the IR-MALDI-2 approach for the highest analytical sensitivity, we characterized the expansion dynamics of the particle plume as generated by the IR laser. Here, we recorded the total ion count and the intensities of selected signals registered from P. aeruginosa samples as a function of the interlaser delay and buffer gas pressure in the ion source. The data revealed that the IR-MALDI-2 ion signals are primarily generated from slow particles having mean velocities of ∼10 m/s. Interestingly, two different pressure/delay time regimes of the optimized ionization efficiency for phospholipids and smaller metabolites, respectively, were revealed, a result pointing to yet-unknown convoluted reaction cascades. The described IR-MALDI-2 method could be a helpful new tool for a microbial mass spectrometry imaging of small molecules requiring little sample preparation.

Pulsed laser ablation of binary compounds: effect of time delay in component evaporation on ablation plume expansion

Pulsed laser ablation of compound materials often occurs with delayed evaporation of a less volatile component; however, the effect of the delay on ablation plume expansion remains virtually unexplored. Here, we have performed an experimental and theoretical study of the delayed evaporation effect using an example of a plume produced by nanosecond laser ablation of a gold–silver alloy in a vacuum and comparing it with ablation of pure gold and silver targets. The plume expansion dynamics are investigated by time-of-flight (TOF) mass spectrometry and direct simulation Monte Carlo (DSMC), while the laser-induced target evaporation is analyzed using a thermal model. A dramatic effect of the delay time on the average kinetic energy of the plume particles, especially for the less volatile gold, is demonstrated and the main collisional processes governing the two-component plume expansion under the conditions of delayed evaporation are revealed. Based on comparison of experimental and DSMC data, the delay of the gold evaporation onset is estimated as approximately 0.6 ns. The delayed evaporation is therefore an important factor for correct interpretation of TOF measurements in ablation plumes with components of different volatilities.

The plasma characteristics of femtosecond-nanosecond dual-pulse laser ablated soil

We report on the observation of dual-pulses laser-produced plasmas (DP-LPPs), following a femtosecond Ti: sapphire pulse laser ablate soil generated asubstantial numberof soil aerosol particle clusters of soil target and then a nanosecond Nd:YAG pulse laser re-ablated the soil aerosol particles clusters. The temporal evolution of the fs laser-produced plasmas (fs-LPPs) highlight a different in plasma plume expansion dynamics and particles clusters distributions where, the initial position and velocity of plasma plume expansion are 0.79 mm and 4.8 km/s, the terminal position is 2.2 mm and the velocity gradually become slower and slower, in the delay time range of 150 ns to 2.1 μs. There are three distribution states contains a columnar particle fluid flow region, “Mushroom cloud” fluid flow region, and arbitrary shape fluid flow region of the particles scattering images of different inter-pulse time at 1, 5, 9, 10, 30, 50, 200, 400 and 800 μs. Based on the Boltzmann plot method and Stark broadening, the plasma temperature and electron density is also investigated, the results shows that DP-LPPs optical emission spectrum (OES) has a narrow linear broadening and enhanced spectral intensity, associates with the higher plasma temperature and lower electron density compare with the single fs-LPPs.

Experimental study of the effect of pressure and laser fluency on laser ablation craters and LIBS emission features of brass sample

We performed measurements on an ablated volume of a brass sample using optical microscopy and spectroscopic analysis of the plasma generated by Nd:YAG laser irradiation. A parametric study was investigated under different gas pressures and laser energy conditions for several time delays in order to determine the laser ablation plume with "ideal" properties. The ablation volume of the brass sample was determined by measuring the volume of the crater after laser ablation. As a result, we have observed that the surrounding gas pressure influences the amount of the ablated material and the expansion dynamics of the plasma plume. The mass fractions of copper, zinc and lead were measured by using CF-LIBS technique. Slight elemental concentration variations, not exceeding 4%, were found when compared with certified values.

Time-resolved quantification of plasma accumulation induced by multi-pulse laser ablation using self-mixing interferometry

In this work a method based on self-mixing interferometry (SMI) is presented for probing the concentration of plasma plumes induced by multi-pulse laser ablation. An analytical model is developed to interpret the single-arm interferometric signal in terms of plasma electron number density. Its time dependence follows a power-law scaling which is determined by concurrent effects of plume accumulation and propagation. The model has been applied for the experimental study of plume formation at variable laser pulse frequencies on different materials. The plume expansion dynamics has been observed with high-speed imaging, and the SMI measurements allowed for a time-resolved estimation of the electron number density. The intrinsic advantages of the SMI technique in terms of robustness and low intrusiveness would allow for its usage as a fast diagnostic tool for the dynamical scaling of laser-induced plumes. Moreover it can be easily applied in laser-based manufacturing technologies where plasma concentration monitoring and control is important.

A Study on the Plasma Plume Expansion Dynamics of Nanosecond Laser Ablating Al/PTFE

To study the plasma plume expansion dynamics of nanosecond laser ablating Al/PTFE, the Al/PTFE propellant was prepared by a molding sintering method and the rapid expansion process of the plasma plume was photographed using fast photography technology. The effects of the proportion of Al, laser energy and ambient pressure on plasma plume expansion dynamics are analyzed. The results show that the plume expansion process of laser ablating Al/PTFE plasma can be divided into three stages and this phenomenon has not been reported in the literature. The Al powder doped in PTFE will block part of the laser transmission into the propellant, thus reducing the laser absorption depth of the propellant. In the case of short pulse laser ablation, the reaction rate between Al and PTFE is optimal when the reductant is slightly higher than the oxidant. As the laser energy increases, the light intensity of the plasma becomes stronger, the plasma size becomes larger and the existence time of plasma becomes longer. In the first stage plume, the plume expands freely at the ambient pressure of 0.005 Pa and the plume expansion distance is linearly related to time, while the shock wave formed at the interface between the plume front and the ambient gas at the ambient pressure of 5 Pa and the expansion can be described by S-T theory.

Expansion of laser-induced plume after the passage of a counter shock wave through a background gas

Double-pulsed laser ablation with two targets and lasers in a background gas is a method to form nanoparticle complex. Effects of pulse delay between two lasers on plume expansion dynamics are discussed. The germanium and silicon targets were set parallel to each other and irradiated by two YAG lasers. The germanium target was irradiated followed by irradiation of the silicon target with delay time, td. We found that the expansion distance of delayed silicon plume is enhanced for 2 µs ≤ td ≤ 50 µs, compared to that when only the silicon target is irradiated. For td = 200 µs, the expansion distance of delayed silicon plume is similar to that when only the silicon target is irradiated. We discuss the expansion dynamics of the delayed silicon plume based on the effect of the density distribution induced by the primary germanium plume. Our results indicate that the effect of primary germanium plume remains up to about td = 50 µs, and it disappears by td = 200 µs.

Experimental Research on Impulse Coupling Characteristics and Plasma Plume Dynamics of a Nanosecond Pulsed Laser Irradiated Aluminum Target

The impulse generated by ablating aluminum targets was investigated in this study using the micro-impulse measurement method with a torsion pendulum, and the plasma plume characteristics were researched using fast photography and optical emission spectroscopy. The experiment was carried out with a pulsed laser with a wavelength of 1064 nm and a pulse duration of 8.7 ns. The fluence varied from 5.69 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 33.67 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The impulse coupling coefficients were obtained from the impulse measurements and the images of the plasma plume were recorded with a gate width of 500 ns. The results indicated that the variation of the impulse coupling coefficient was affected by the change of the laser fluence and the decline of the coefficient at high fluence was because of the plasma shielding effect. The intense radiation region located above the target surface in the corresponding plume was evident. Additionally, the differential coupling coefficient was presented and compared with the impulse coupling coefficient. The plasma temperature and the electron number density were estimated with the Boltzmann plot method and the Stark broadening method, respectively, using optical emission spectroscopy. Furthermore, the relative energy coupling efficiency was deduced from the plume front positions to determine the influence of the plume expansion dynamics on the impulse coupling. The obtained results showed that the variation trend of efficiency versus the laser fluence was similar to that of the impulse coupling coefficient.

Wavelength-dependent variations of the electron characteristics in laser-induced plasmas: A combined hydrodynamic and adiabatic expansion modelling and time-gated, optical emission imaging study

The spatial and temporal evolution of the absolute electron densities and temperatures in plasmas formed by nanosecond pulsed laser ablation of silicon in vacuum at two wavelengths (1064 and 532 nm), at similar irradiances, have been explored by complementary simulation (using combined hydrodynamic and adiabatic models) and experiment. Modelling the laser-target and laser-plume interactions with the POLLUX code reveals the evolving composition and dynamics of the laser induced plasma (LIP) during the incident laser pulse: 532 nm irradiation causes more ablation, but the LIP formed by 1064 nm excitation has a higher average charge state and expands faster. The experimental data, from the analysis of Stark broadened line shapes of SiIII and SiIV cations in time-gated, position- and wavelength-resolved images of the plume emission, allow characterisation of the plume dynamics at later times. These dynamics are compared with predictions from two forms of adiabatic expansion model. Both take as input parameters the plume properties returned by the POLLUX simulations for the end of the laser pulse, but differ according to whether the initial plasma is assumed isothermal or isentropic. The study illustrates the important λ-dependences of the target absorption coefficient (in establishing the ablated material density) and of electron–ion inverse bremsstrahlung absorption (in coupling laser radiation into the emergent plasma); the extents to which these interactions, the relative ablation yields, and the plume expansion dynamics depend on λ; and the importance of identifying appropriate initial conditions for adiabatic expansion modelling of LIP in vacuum.

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.

Evaluation of pressure in a plasma produced by laser ablation of steel

We investigated the time evolution of pressure in the plume generated by laser ablation with ultraviolet nanosecond laser pulses in a near-atmospheric argon atmosphere. These conditions were previously identified to produce a plasma of properties that facilitate accurate spectroscopic diagnostics. Using steel as sample material, the present investigations benefit from the large number of reliable spectroscopic data available for iron. Recording time-resolved emission spectra with an echelle spectrometer, we were able to perform accurate measurements of electron density and temperature over a time interval from 200 ns to 12 μs. Assuming local thermodynamic equilibrium, we computed the plasma composition within the ablated vapor material and the corresponding kinetic pressure. The time evolution of plume pressure is shown to reach a minimum value below the pressure of the background gas. This indicates that the process of vapor-gas interdiffusion has a negligible influence on the plume expansion dynamics in the considered timescale. Moreover, the results promote the plasma pressure as a control parameter in calibration-free laser-induced breakdown spectroscopy.

Effect of counter shock wave on the expanding plume

Effects of head on collision on two laser ablation plumes in background gas are revealed by observation of plume expansion dynamics. Nb2O5 and Ni targets were set parallel to each other and irradiated simultaneously by two YAG lasers in He gas under various gas pressures. The plume expansion dynamics was monitored by a gated ICCD camera. The plumes stagnate at 500 Pa after collision of two plumes. The backward movements of the plumes are observed above 2000 Pa, even though the plumes do not collide with each other. We estimated propagation of shock front by point blast model and the results indicate that the backward movement at high background gas pressure is due to the collision between plume and shock front. These results indicate that collision with counter shock wave is very important for plume expansion dynamics.

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

Abstract The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fluoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin film deposition. Specifically, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fluoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fluoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fluence profile. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fluoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.

Dynamics of colliding laser ablation plumes in background gas

We observed plume expansion dynamics during pulsed laser ablation in background gas when two plumes collided head-on. The Si target is irradiated followed by the Ge target with delay time t d. When t d is larger than a few μs, the Si plume emission quenches before the irradiation of the Ge target. Re-emission of quenched Si atomic species by the collision with counter Ge plume is observed. The intensity and lifetime of Si re-emission decrease with increasing t d, and rapid decrease at around t d = 60 μs is observed. These results indicate that non-luminescent Si atomic species exist between targets up to about t d = 60 μs and effects of the collision rapidly decrease at above about t d = 60 μs. Effects of the collision of Si and Ge plumes and the re-emission of quenched Si atomic species are discussed.