Experimental study on the dynamics and parameters of nanosecond laser-induced aluminum plasma

In this study, the influence of laser energy and pressure on propulsion performance of zinc and acrylonitrile butadiene styrene (ABS) is investigated by impulse measurement, fast exposure images, spectral diagnostics and target ablation. A Q-switched Nd:YAG laser with the wavelength of 1064 nm and pulse width of 6 ns is employed. The impulse and coupling coefficient generated by laser ablation ABS are greater than that of Zn, and they exhibit a similar variation trend with pressure. However, at higher pressure levels, the change in impulse versus laser energy is not completely coincident between Zn and ABS samples. The target property plays a significant role in the generation and propagation of plume related to the plasma parameters such as electron density and temperature. The temporal evolution images indicate that the plasma plume of laser-induced Zn presents a faster decay in comparison with that of ABS, which is ascribed to the fact that the gas temperature of ABS is higher than the electron temperature of Zn plasma in the local thermodynamical equilibrium. Also, the electron density is lower for Zn due to the rapid heat diffusion and higher ablation threshold of metal. It is found that the surface absorption is dominant for metal because the ablated crater of Zn performs larger diameter and shallower depth. On the contrary, the shrinkage in diameter but enhancement in depth of crater is observed from ABS surface, and the ablation mass is larger, suggesting the obvious volume absorption for polymer. The results reveal that the target property can engender an important effect on the energy conversion between laser, target and plasma.

Time-resolved Emission Spectroscopy of Impact Plasma

We report on the effect of laser fluence variation on ablation rate and the time-integrated optical emission of copper plasma in the presence of static transverse magnetic field in air. In the presence of magnetic field, the ablation rate at 14 Jcm−2 laser fluence is around two times higher than that in the absence of magnetic field. It is attributed to an increase in melt ejection caused by recoil pressure of ablated mass in the presence of magnetic field. We also simulated the laser ablation rate using finite element method to justify that the ablation rate is higher in the presence of magnetic field. The intensity of atomic/ionic transition is enhanced in the presence of magnetic field. The enhancement in the intensity of spectral line depends on laser fluence and it is pronounced at fluence 14 Jcm−2. The intensity enhancement is due to an increase in electron-impact excitation and recombination process as a result of magnetic confinement of plasma. The ionic line also showed intensity enhancement in the presence of the magnetic field. It is due to the increase in ionization of atom in the presence of magnetic field. The ionization potential is lowered in the presence of magnetic field which results in more ionization. The electron density and temperature initially increased with fluence and then decreased slightly at higher fluence. In the presence of magnetic field, the electron density and temperature followed the same trend; however, higher compared with that in the absence of magnetic field. It is attributed to magnetic confinement of plasma. The spatially resolved optical emission measurements showed that the intensity with magnetic field decreased with lateral distance. However, it is higher than that without magnetic field up to 2 mm and beyond that the intensity with and without magnetic field remained almost the same.

Comparison of the measured and modeled electron densities and temperatures in the ionosphere and plasmasphere during 14–16 May 1991

The electron temperature and the density of argon arc plasma plume injected into water were observed through optical emission spectroscopic measurement. Argon arc plasma jets were generated with a DC arc current of 40–200 A by a non‐transferred arc discharge plasma torch under atmospheric pressure, and ejected through a nozzle on the anode into water or gas‐phase argon. The electron temperature of the plasma plume was determined by the Boltzmann plot with line intensity measurement of atomic argon lines, while the electron density is examined with the Stark broadening measurement of Hα line. It was found that the electron temperature increased from approximately 6500–8000 K, and the electron density also increased up to the order of 1016cm−3, as the discharge current increased for the underwater argon arc plasma plume, both of which were observed at 20 mm in the downward direction from the plasma generator nozzle. In addition, the electron temperature of the underwater plasma plume was slightly lower than that of the gas‐phase argon plasma plume, while the electron density of the underwater plasma was slightly higher than that of the gas‐phase plume. Longitudinal variation of the electron temperature and density of the underwater plasma plume was also observed, and the lowering rate was found to depend on the arc discharge current. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Helicobacter felis infection in mouse alters the amount of peripheral blood phagocytic leukocytes

In this present work, electron temperature and electron density in Laser Induced Plasma (LIP) of Stainless Steel (SS) in air as a function of laser energy is presented. The emitted lines of Fe I at 351.0 nm, 373.5 nm, 397.5 nm are identified in LIP of SS. The electron temperature is obtained via Boltzmann plot from the relative intensity of these emitted lines. Electron density was determined from the stark broadening of Fe~I lines at 375.5 nm. The electron density and temperature were measured at three different laser energies; 50 mJ, 60 mJ and 70 mJ. The electron temperature and electron density are found to be 0.145, 0.149 and 0.141 eV and \(2.64\times 10 ^{18}\), \(2.66\times 10 ^{18}\) and \(2.54\times10 ^{18}\) cm\(^{-3}\), respectively. The fall in both parameters can be explained due the plasma shielding effect at high energyof laser beam.

Two techniques are applied to diagnose characteristic parameters of plasma created by hypervelocity impact, such as electron temperature and electron density. The first technique is a sweep Langmuir probe (SLP), which is a new apparatus based on a dual channel circuit that can compensate for stray capacitance and obtain a good synchronicity, so that electrostatic turbulence with a good temporal resolution can be acquired. The second technique is a triple Langmuir probe (TLP), which is an electrostatic triple Langmuir probe diagnostic system, in which no voltage and frequency sweep is required. This technique allows to measure electron temperature, electron density as a function of time. Moreover, the triple Langmuir probe diagnostic system allows the direct display of electron temperature and semidirect display of electron density by an appropriate display system, the system permits us to eliminate almost all data processing procedures. SLP and TLP were applied to obtain fluctuations of the characteristic parameters of plasma generated by hypervelocity impact. As an example of their application to time-dependent plasma measurement, the electron temperature and electron density of plasmas were acquired in hypervelocity impact experiments. Characteristic parameters of plasma generated by hypervelocity impact were compared by the two kinds of diagnostic techniques mentioned above.

In order to understand in depth plasma behavior during ultra-high power fiber laser deep penetration welding, the plasma inside and outside the keyhole is observed, and the spectrum of fiber laser-induced plasma is measured and analyzed. Based on the measured data of plasma, the electron temperature and electron density, ionization degree and pressure are calculated, and the characteristics of plasma parameters at different values of keyhole depth and outside the keyhole are investigated. The results indicate that the distribution of plasma inside the keyhole is uneven, and the vapor plume is much bigger outside the keyhole. The spectrum of plasma show that the fiber laser-induced plasma is weakly ionized and radiates a few spectral lines. The further calculation results also confirm that the plasma induced by fiber laser is in a weakly ionized state. However, the electron density of plasma still stays in a high level, and the transient pressure of plasma is up to hundreds of times as large as atmospheric pressure.

The microwave induced plasmas have been successfully used as an excitation source in atomic emission and mass spectrometry for the analytical determination of substances. In this work a study of the influence of the thermodynamic equilibrium state over the capacity of sample excitation of an argon plasma flame sustained by a surface wave at atmospheric pressure is presented. The state of the thermodynamic equilibrium in the discharge is determined by the relation between its temperatures and densities. The values of these parameters depend on the energy available in the discharge, which is also responsible for the excitation of the samples introduced into the plasma. We have compared the behavior of two characteristic parameters of plasma (electron density and temperature) and of the ArI level population with the microwave power. The results have shown that the values of these parameters and populations had a tendency to remain constant for microwave powers above a certain value. Thus, from 100 W only a part of the energy injected into the discharge is absorbed in the plasma and the plasma equilibrium state is not consequently modified. This behavior is the same as that found for atomic lines of both halogens and iron introduced as samples into the plasma and seems to show that if the plasma is close to thermodynamic equilibrium the excitation of the samples is favored.

The aim of this work is to analyse and discuss a spectroscopic method of diagnosis based on the Stark broadening of emission lines to determine the electron density and temperature in atmospheric-pressure plasmas. Usually, when the electron temperature is previously known, the Stark broadening of certain spectral lines spontaneously emitted by the plasma is used to determine the electron density in a rapid and inexpensive way. However, comparing two or more broadening of lines can allow us to diagnose the electron density and temperature simultaneously. To carry out this cross-point method, we must know the Stark broadening dependence on the electron temperature and density for different lines. In this work we have used the first three Balmer series hydrogen lines, whose Stark broadenings were calculated by means of a recent micro-field model existing in the bibliography. The experimental study was made in argon and hydrogen plasma flames. The plasmas were produced at 2.45 GHz by an axial injection torch, which can operate at atmospheric pressure under different experimental conditions to produce appropriate plasmas in ‘open air’. The flame produced in this way is a two-temperature plasma, so it is not in local thermodynamic equilibrium. Moreover, by means of the Boltzmann-plot modified with the p−6 law, we found for the hydrogen plasma that most of the observable atomic states were ruled by the excitation–saturation balance. With this method we could also determine the electron temperature.

An 80 kJ electrothermal gun facility was assembled at Kumamoto University in order to investigate the dependence of capillary discharges on ambient pressure. The observation of capillary discharges using an image converter camera shows that early phenomena of the discharges vary with ambient pressure. At a pressure of one atmosphere, discharges begin to occur near the radial center of the capillary. On the other hand, at a lower pressure of about 1 Pa, discharges occur near the insulator surface of the capillary. Plasma parameters, such as electron density, electron temperature, and the species of the plasma and neutral gas, are measured by spectroscopic techniques. The electron density at low pressure is more than 10/sup 17/ cm/sup -3/ at a current of only about 1 kA because of severe wall ablation by the surface discharge. At high pressure, the electron density is quite low for electron currents less than 2 kA. For currents greater than 2 kA, the electron density is over 10/sup 18/ cm/sup -3/ at both pressures. The temperature estimated from a Boltzmann plot is in the range of 0.6 eV to 0.7 eV at low pressure.

Study of spectral intensity of the laser ablated tungsten plasma and ablation mass at various laser spot sizes and laser fluence in vacuum environment

The arc discharge plasma is one of the efficient technique to fabricate nano-structures such as nanotubes, nanoparticles and thin films, which have variety of technological applications. In this study, plasma dynamics such as the electron density and temperature for arc discharge carbon plasma in methane ambient environment is presented to investigate the impact and contribution of physical parameter as arc current and ambient pressure on the plasma dynamics. The electron temperature and density is estimated applying in situ optical emission spectroscopy. The optical spectra are recorded for applied arc current 50A, 60A, 70A, 80A and 90A for ambient pressures 100torr, 300torr and 500torr. A rise in electron temperature and electron density is detected with increase in applied arc current and ambient pressure. The obtained results reveal that in arc discharge process, the arc current and ambient pressure have significant contribution towards the kinetics of the plasma species.

The optical emission spectroscopy technique is used to determine the vibrational temperature of the second positive band system, N_{2} (C,upsilon^{^{prime}} - B,upsilon^{^{primeprime}}) in the wavelength range 367.1–380.5 nm by using the line-ratio and Boltzmann plot methods. The electron temperature is evaluated from the intensity ratio of the selected molecular bands corresponding to N_{2}^{ + } (B,upsilon - X, upsilon^{^{prime}} , 391.44 nm), and, N_{2} (C,upsilon^{^{prime}} - B,upsilon^{^{primeprime}}, 375.4 nm) transitions, respectively. The selected bands have a different threshold of excitation energies and thus serve as a sensitive indicator of the electron energy distribution function (EEDF). The electron density has been determined from the intensity ratio of the molecular transitions corresponding to N_{2}^{ + } (B,upsilon - X, upsilon^{^{prime}} , 391.44 nm), and, N_{2} (C,upsilon^{^{prime}} - B,upsilon^{^{primeprime}}, 380.5 nm) for different levels of pressure and radio frequency power. The results show that the vibrational temperature decreases with increasing nitrogen fill pressure and radio frequency power. However, the electron temperature increases with radio frequency power and reduces with fill pressure. The electron density increases both with nitrogen fill pressure and radio frequency power that attributes to the effective collisional transfer of energy producing electron impact ionization. Plasma parameters show a significant dependence on discharge conditions and can be fine-tuned for specific surface treatments.Article HighlightsSpectrum analysis of RF-driven nitrogen plasma for varying discharge conditionsEvaluation of vibrational temperature using line-ratio and Boltzmann plot methodsComparison of vibrational temperatures for line-ratio and Boltzmann plot methodsEvaluation of electron temperature and density using the intensity-ratio of bandsCorrelation of temperature and density with varying fill pressure and RF power