Dynamics Of Laser-induced Plasma Research Articles

Dynamics of laser-induced plasma and cavitation bubble at high pressures and the impacts on underwater LIBS signals

Characteristics of laser-induced plasma depends strongly on its ambient pressure, and a deeper understanding of the high pressure impact on the underwater plasma emission is essential for the application of LIBS in the deep-sea. In this work, we investigated the temporal evolution of underwater plasma and cavitation bubble at the high pressures up to 50 MPa, by using fast imaging and shadowgraph techniques. It showed that as the ambient pressure increases, the plasma expansion is much suppressed with a stronger emission intensity and a slower emission decay, but it quenches much earlier and ends with a sharp drop at the higher pressures. From the shadowgraph imaging results, it showed that the increase in pressure has a great impact on the bubble evolution. Both the bubble maximum radius and the bubble lifetime decrease dramatically with the pressure as a consequence of faster dynamics. By comparing between the plasma and bubble results, we demonstrated the critical role of bubble dynamics on the characterization of plasma emission at high pressures. At relatively low pressures, the bubble expansion time is long enough to finish the plasma radiation. While at high pressures, strong bubble-plasma interaction occurs that will guide the plasma evolution behavior at the late stage. The plasma can gain energy from the confinement effect caused by the bubble shrinking process which leads to an increase in the emission intensity, but it will quench immediately after the bubble collapse. Such effects caused by bubble dynamics at high pressures explain well the evolution behaviors of underwater LIBS signals of OH, Ca II, Ca I, and CaOH, considering the different lifetimes of these emitting species in the plasma. This work reveals the complex impacts of high pressure on underwater plasma emissions and underwater LIBS signals.

Early dynamics of laser-induced plasma and cavitation bubble in water

The knowledge of early laser-induced plasma and cavitation bubble dynamics are of great importance for a better understanding of underwater laser-induced breakdown spectroscopy. In this work, we investigated the temporal evolution of the plasma and bubble at an early stage before 2 μs, by using fast imaging and shadowgraph techniques. It showed that the initial plasma forms at the laser focal point and then grows up toward the incident laser. As time evolves, the plasma expands simultaneously forward and backward to its peripheral region and a sub-plasma structure can be observed at low laser energies. The plasma has a good pulse-to-pulse repeatability during the laser pulse, while soon after the laser pulse (from 20 to 50 ns), it undergoes a severe pulse-to-pulse fluctuation with an inhomogeneous emission distribution. At longer times, the plasma becomes much stable again. To clarify the interrelationship between the bubble dynamics and the plasma characteristics, shadowgraph images of the bubble were shown and compared with the plasma images. It showed that the morphology of the bubble and its evolution have a good consistency with the morphology of plasma. The bubble radius as a function of time can be well expressed by the equation R=at0.4, and a is a constant related to the laser energy. By inspecting the evolution curve of the bubble wall and the bubble pressure calculated based on the Gilmore model, a transition phase from 20 to 50 ns can be identified between the moving breakdown phase and the thermal expansion phase. In this transition phase, both the bubble expansion speed and the bubble pressure drop drastically that may account for the severe plasma fluctuations as observed in this period. These results of early bubble dynamics provide insights into the critical role of bubble-plasma interaction on the characterization of laser-induced plasma in water.

Anisotropic Surface Broadening and Core Depletion during the Evolution of a Strong-Field Induced Nanoplasma

Strong-field ionization of nanoscale clusters provides excellent opportunities to study the complex correlated electronic and nuclear dynamics of near-solid density plasmas. Yet, monitoring ultrafast, nanoscopic dynamics in real-time is challenging, which often complicates a direct comparison between theory and experiment. Here, near-infrared laser-induced plasma dynamics in $\ensuremath{\sim}600\text{ }\text{ }\mathrm{nm}$ diameter helium droplets are studied by femtosecond time-resolved x-ray coherent diffractive imaging. An anisotropic, $\ensuremath{\sim}20\text{ }\text{ }\mathrm{nm}$ wide surface region, defined as the range where the density lies between 10% and 90% of the core value, is established within $\ensuremath{\sim}100\text{ }\text{ }\mathrm{fs}$, in qualitative agreement with theoretical predictions. At longer timescales, however, the width of this region remains largely constant while the radius of the dense plasma core shrinks at average rates of $\ensuremath{\approx}71\text{ }\text{ }\mathrm{nm}/\mathrm{ps}$ along and $\ensuremath{\approx}33\text{ }\text{ }\mathrm{nm}/\mathrm{ps}$ perpendicular to the laser polarization. These dynamics are not captured by previous plasma expansion models. The observations are phenomenologically described within a numerical simulation; details of the underlying physics, however, remain to be explored.

Theoretical study of soft X-ray emission and dynamics of laser-induced plasma of double stream gas puff

The double stream gas puff-based laser-produced plasma is studied as a source of soft X-ray radiation in nm wavelength spectral range. Dynamics of plasma induced by Nd:YAG laser beam and its emission is simulated with radiation-magnetohydrodynamic code Zstar. The modeling results for krypton gas stream in an annular helium jet as a circumferential gas for various picosecond and nanosecond laser pulses corresponding to the experiments are presented. The spatial–spectral features and temporal behavior of the soft X-ray and EUV emission are investigated. Under ps pulse, the gas is rapidly ionized in the laser beam channel, but it does not have enough time to shift sensibly during the pulse, and the plasma electron density grows against the background of almost constant ion density during the ionization in the laser radiation field. There is ionization instability only capable to be developed in ps range. At ns pulse, the gas ionization and heating leads to gas pushing out of the channel, and the formation of a divergent compression wave transforming into the shock wave. Behind the compression wave front, conditions arise for the development of Rayleigh–Taylor-type instability. The instability leads to the redistribution of plasma temperature and density, and to the formation of increased soft X-ray emission spots. Time evolution of spatial distributions and spectral characteristics of emitted SXR radiation is analyzed for different laser pulses. Transient effects in multicharged ion plasma are discussed, fundamental understanding of those is required for optimization of plasma radiation source. A conversion efficiency of laser energy into soft X-ray wavebands from krypton plasma is scanned by laser parameters and analyzed.

Effect of sample temperature on spectroscopic investigation of laser-induced aluminum and copper plasma

In this work, the influence of samples temperature and laser energy on the optical emission spectra and plasma parameters of laser-induced breakdown spectroscopy for aluminum and copper metallic target is investigated. The samples are uniformly cooled down to −70 °C and heated up to 200 °C by an external liquid nitrogen and ceramic heater, respectively. The plasma formed is generated by ablating the surface targets using Nd:YAG laser with laser energies of 100 mJ, 200 mJ and 300 mJ. The emission spectra at ambient atmospheric pressure are recorded using HR4000 spectrometer. From these spectra, plasma temperatures and electron densities are determined by using Boltzmann plot and Stark broadening methods, respectively. A significant increase in the peak intensity of spectral lines is observed with increase in the laser energy as well as sample temperature for both elements. Both of these parameters have shown a clear influence on dynamics of laser-induced plasma for each species. In brief, both laser energy and sample temperature affect the emission intensity, temperature and density of the laser-induced plasma generated from aluminum and copper samples.

Dynamics and its modulation of laser-induced plasma and shockwave in femtosecond double-pulse ablation of silicon

The dynamics of laser-induced plasma and shockwave was studied using time-resolved shadowgraphy in femtosecond double-pulse ablation of silicon. The morphology and expansion distances of laser-induced plasma and shockwave can be controlled by adjusting the pulse delay. The underlying mechanism was interpreted in terms of suppressed laser-induced air breakdown and enhanced laser energy deposition. The former is proposed to reduce the expansion distance in the longitudinal direction for small pulse delay, while the latter is the dominant mechanism for increasing the expansion distance in the longitudinal and radial directions for pulse delay exceeding a few picoseconds.

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.

Pulse width dependent dynamics of laser-induced plasma from a Ni thin film

Plasma plume formation and its expansion in the background gas are investigated in a 50 nm thick Ni thin film under the rear ablation/laser blow-off (LBO) geometry, employing 10 ns, 200 ps and 100 fs laser pulses respectively. Plume directionality, splitting and expansion are found to depend on the laser pulse width, and the expansion behavior is explained by appropriate models. In the case of fs ablation, the plume shows a linear expansion at lower background pressures, while at higher pressures the expansion appears to show shock wave like nature. For ps ablation the expansion appears to follow a blast wave model at lower pressures, which, however, fits with drag model at higher pressures. In case of ns ablation, shock wave like nature is observed for all the pressures. Further, we believe the present study may have potential implications in pulsed laser deposition, ultra fast laser based nano particle generation and micro-machining.

Evaporation of an anisotropic nanoplasma

Intense laser induced plasma dynamics in sub-micron scale helium droplets are monitored by femtosecond time-resolved X-ray coherent diffractive imaging. Anisotropic surface softening and strongly anisotropic shrinking of the plasma core are observed.

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.

Laser-Induced Graphite Plasma Kinetic Spectroscopy under Different Ambient Pressures**Supported by the FRGS under Grant No R.J130000.7809.4F519.

The laser induced plasma dynamics of graphite material are investigated by optical emission spectroscopy. Ablation and excitation of the graphite material is performed by using an 1064nm Nd:YAG laser in different ambient pressures. Characteristics of graphite spectra as line intensity variations and signal-to-noise ratio are presented with a main focus on the influence of the ambient pressure on the interaction of laser-induced graphite plasma with an ambient environment. Atomic emission lines are utilized to investigate the dynamical behavior of plasma, such as the excitation temperature and electron density, to describe emission differences under different ambient conditions. The excitation temperature and plasma electron density are the primary factors which contribute to the differences among the atomic carbon emission at different ambient pressures. Reactions between the plasma species and ambient gas, and the total molecular number are the main factors influencing molecular carbon emission. The influence of laser energy on the plasma interaction with environment is also investigated to demonstrate the dynamical behavior of carbon species so that it can be utilized to optimize plasma fluctuations.

Classification and stability of plasma motion in periodic linearly polarized relativistic waves

Based on a relativistic fluid-Maxwell model, laser-induced plasma dynamics is investigated for relativistic periodic waves. Within a one-dimensional (1D) description, the Akhiezer–Polovin model is applied to the existence of periodic, nonlinearly coupled electromagnetic and electrostatic waves, and the corresponding particle motion. Known existence criteria for periodic solutions are generalized. The corresponding stability behaviors are investigated by 1D integrators of the relativistic fluid-Maxwell model. It is shown that in contrast to the vacuum solution, linearly polarized coupled electromagnetic-electrostatic waves are unstable in plasmas. The magnitudes of the growth rates are investigated in terms of the maximum amplitudes and normalized phase velocities.

Ultrafast electron beam imaging of femtosecond laser-induced plasma dynamics

Plasma dynamics in the early stage of laser ablation of a copper target are investigated in real time by making ultrafast electron shadow images and electron deflectometry measurements. These complementary techniques provide both a global view and a local perspective of the associated transient electric field and charge expansion dynamics. The results reveal that the charge cloud above the target surface is composed predominantly of thermally ejected electrons and that it is self-expanding, with a fast front-layer speed exceeding 107 m/s. The average electric field strength of the charge cloud induced by a pump fluence of 2.2 J/cm2 is estimated to be ∼2.4×105 V/m.

Effect of applying static electric field on the physical parameters and dynamics of laser-induced plasma

In order to improve the performance of the LIBS technique – in particular its sensitivity, reproducibility and limit of detection – we studied the effect of applying a static electric field with different polarities on the emission spectra obtained in a typical LIBS set-up. The physical parameters of the laser-induced plasma, namely the electron density N e and the plasma temperature T e , were studied under such circumstances. In addition to the spectroscopic analysis of the plasma plume emission, the laser-induced shock waves were exploited to monitor the probable changes in the plasma plume dynamics due to the application of the electric field. The study showed a pronounced enhancement in the signal-to-noise (S/N) ratio of different Al, neutral and ionic lines under forward biasing voltage (negative target and positive electrode). On the other hand, a clear deterioration of the emission line intensities was observed under conditions of reversed polarity. This negative effect may be attributed to the reduction in electron-ion recombinations due to the stretched plasma plume. The plasma temperature showed a constant value in the average with the increasing electric field in both directions. This effect may be due to the fact that the measured values of T e were averaged over the whole plasma emission volume. The electron density was observed to decrease slightly in the case of forward biasing while no significant effect was noticed in the case of reversed biasing. This slight decrease in N e can be interpreted in view of the increase in the rate of electron–ion recombinations due to the presence of the electric field. No appreciable effects of the applied electric field on the plasma dynamics were noticed.

Study of early laser-induced plasma dynamics: Transient electron density gradients via Thomson scattering and Stark Broadening, and the implications on laser-induced breakdown spectroscopy measurements

To further develop laser-induced breakdown spectroscopy (LIBS) as an analytical technique, it is necessary to better understand the fundamental processes and mechanisms taking place during the plasma evolution. This paper addresses the very early plasma dynamics (first 100 ns) using direct plasma imaging, light scattering, and transmission measurements from a synchronized 532-nm probe laser pulse. During the first 50 ns following breakdown, significant Thomson scattering was observed while the probe laser interacted with the laser-induced plasma. The Thomson scattering was observed to peak 15–25 ns following plasma initiation and then decay rapidly, thereby revealing the highly transient nature of the free electron density and plasma equilibrium immediately following breakdown. Such an intense free electron density gradient is suggestive of a non-equilibrium, free electron wave generated by the initial breakdown and growth processes. Additional probe beam transmission measurements and electron density measurements via Stark broadening of the 500.1-nm nitrogen ion line corroborate the Thomson scattering observations. In concert, the data support the finding of a highly transient plasma that deviates from local thermodynamic equilibrium (LTE) conditions during the first tens of nanoseconds of plasma lifetime. The implications of this early plasma transient behavior are discussed in the context of plasma–analyte interactions and the role on LIBS measurements.

A new model for studying the plasma plume expansion property during nanosecond pulsed laser deposition

A physical model is proposed to study the laser-induced plasma dynamics expansion during irradiation of material by a high-intensity nanosecond pulsed laser beam. Based on a consideration of the plasma ionization effect and local conservations of mass, momentum and energy, combined with the assumption that plasma can be viewed as a compressible ideal fluid and a high temperature–high pressure ideal gas, we developed a new dynamics expansion mechanism for plasma produced by pulsed laser radiation. A set of new plasma expansion dynamics equations based on our model are first deduced. Then, taking the example of the carbon target, using the finite difference method, the plasma flow dynamics into a vacuum, such as plasma spacial number density distribution, plasma number density and velocity evolvement in radial and axial directions, are studied in detail. The results show that there are some main factors affecting the velocity distribution of the plasma, including the temperature of the plasma, the ionization fraction of the plasma and the dynamic source provided by the vaporized material. The velocity uz in the longitudinal direction is different from ur in the transverse direction because of huge initial eject velocity and evaporated dynamic source. The velocities of the plasma calculated by this model are found to be in better agreement with the experimental results derived from the work of Sanz et al (1985 Plasma Phys. Control. Fusion 27 329) compared with the conventional model.

Time resolved laser-induced plasma dynamics

The structure and evolution of the laser-induced vapor plume and shockwave were measured from femtosecond time resolved shadowgraph images. By changing the wavelength of the probe beam (400 and 800 nm), differences in the opacity of the vapor plume were measured as a function of delay time from the ablation laser pulse. The evolution of the temperature and electron number density during and after the ablation laser pulse were determined and compared for ablation in argon and helium background gases. A laser supported detonation wave (LSD) observed for ablation in argon, blocks the incoming laser energy and generates a high-pressure region above the vapor plume.

Modeling of radiation transfer and emission spectra in laser-induced plasma of Al vapor

The influence of radiation transfer on dynamics of laser-induced plasma of Al vapor is analyzed numerically. Mathematical description of the plasma is performed in the framework of the transient 2D radiation gas dynamics (RGD); the multi-group diffusion approximation with 7–1000 spectral intervals is used to describe plasma radiation transfer. The performed research allows us to conclude that radiative transfer substantially affects the expansion of laser plasma for the nanosecond action intensity of 10 9– 2×10 10 W/ cm 2 and the pulse energies of 0.02– 0.4 J . The radiative energy losses can reach 60% of the laser pulse energy absorbed by the plasma. The spectral composition of escaping radiation is non-equilibrium and qualitatively corresponds to the optically thin approximation. The application of the Planck averaging technique make it possible to predict the correct values of total quantities (integrated over the entire frequency spectrum) using several tens of groups.