Inverse Bremsstrahlung Absorption Coefficient Research Articles

Influence of plasma inhomogeneity and ohmic heating on the nonlinear absorption of intense laser pulse in collisional magnetized plasma

AbstractThe nonlinear absorption in the interaction of an intense laser pulse with a collisional magnetized plasma is studied by considering the effects of plasma inhomogeneity, ohmic heating, and ponderomotive force. For this purpose, we obtain the plasma electron density, the effective dielectric permittivity, and the wave equation using the Maxwell and hydrodynamic equations and solve this equation by the Runge–Kutta numerical method. The results are shown that by increasing the plasma inhomogeneity, the inverse bremsstrahlung absorption coefficient is increased, and also the density ramp parameter and its sign can affect more the absorption coefficient than the temperature ramp parameter . However, when the initial electron density and temperature increase, the laser field amplitude and the absorption coefficient are increased and the spatial damping rate of the laser pulse becomes highly peaked inside the plasma. It is shown by increasing laser pulse energy, the nonlinear bremsstrahlung absorption coefficient is decreased significantly. The results also indicate that by increasing the external magnetic field, the dielectric permittivity is decreased while the laser energy spatial damping, and the absorption coefficient are increased. Moreover, it is found that by considering the ohmic heating effect, the electrons absorb further energy from the fields and consequently the nonlinear absorption is increased.

Comprehensive Analysis of Copper Plasma: A Laser-Induced Breakdown Spectroscopic Approach

The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedical field, electronics, space physics, and material processing necessitates a comprehensive understanding of plasma parameters. The present work delineates the structure and evolution of copper plasma under different ambient pressures (0.01 mbar to 100 mbar) along with other plasma parameters. The study reveals the role of ambient pressure in the increase of plasma temperature (Te), electron density (Ne), number of particles in the Debye sphere, plasma frequency, inverse bremsstrahlung absorption coefficient, electron thermal velocity, electron–ion collision frequency and in the decrease of Debye length (λD) and plasma skin depth (PSD). The experimental techniques and the theoretical explanations for the variation of plasma parameters and their applications are also detailed. As the ambient pressure increases, the motion of plasma species becomes restricted, resulting in the increase of Te, calculated using the Boltzmann plot. From the values of λD, PSD, and Ne, it is understood that the copper plasma under investigation is thermally non-relativistic and satisfies McWhirter’s criterion, thus, revealing the local thermodynamic equilibrium condition of plasma. The effects of Debye shielding and stark broadening on the spectral lines are also investigated. Thus, the study helps bring newfangled dimensions to the application of plasma by exploring the possibility of tailoring plasma parameters.

Laser-Ablated SiO2:TiO2 Plasma Optical Emission Spectroscopy

Laser ablation of sintered SiO2:TiO2 targets using Nd:YAG lasers at fundamental (1064[Formula: see text]nm) harmonic generation in the air has been studied using optical emission spectroscopy. Exploring the spatial fluctuations in electron temperature ([Formula: see text]) and electron density ([Formula: see text]), there is a discussion of how laser energy affects electron temperature ([Formula: see text]) and electron density ([Formula: see text]). Laser energy has also been shown to affect the intensity and velocity of neutral and ion species. Using existing data and theory, the findings were confirmed following the local thermodynamic equilibrium (LTE) hypothesis. Plasma properties such as Debye length ([Formula: see text]), ([Formula: see text]) and plasma frequency ([Formula: see text]) were also studied in this study. Using a laser, we found that all plasma parameters were affected. In addition, the calculated inverse Bremsstrahlung absorption coefficients ([Formula: see text]) were altered.

Simulation of the inverse bremsstrahlung absorption by plasma plume in laser penetration welding

This work employs the Particle-In-Cell method to evaluate the electron inverse bremsstrahlung absorption occurring in the interaction of laser and plasma under deep penetration welding conditions, with focus on the dependence of the inverse bremsstrahlung absorption coefficient on plasma and laser working parameters. When the laser intensity is small, about in the range of industrial applications, the inverse bremsstrahlung absorption coefficient is positively correlated with the electron density, coulomb logarithm and laser wavelength, and inversely correlated with electron temperature. When the laser intensity is high, the inverse bremsstrahlung absorption coefficient does not change significantly, regardless of plasma working parameters.

Inverse bremsstrahlung absorption in magnetized plasmas

The Magneto-Inertial Fusion (MIF) approach has the benefits of both approaches of Inertial Confinement Fusion (ICF) and Magnetic Confinement Fusion (MCF). MIF is a complete approach, as compared to others. It has the advancement of the common ICF and some advantages over MCF. It also includes high-density plasma in the presence of strong magnetic fields. In this study, we investigate the inverse bremsstrahlung absorption (IBA) in magnetized plasma and the kinetic theory. Many researchers have calculated the inverse bremsstrahlung absorption coefficient through the ICF approach. In this investigation, however, the average of IBA is obtained that can be used in the MIF approach, the kinetic theory and the Krook collision frequency. In addition, the influences of some parameters such as laser wavelength, electron temperature, and static magnetic field are shown on the mean collisional absorption. A numerical solution is also used to calculate the dispersion function and the laser electric field. IBA is one of the basic heating processes in laser fusion plasma. The results of the study show that, in critical layers, the increase of absorption is proportional to short laser wavelength, low electron temperature, but IBA varies slowly with the static magnetic field.

Energy penetrated and inverse bremsstrahlung absorption co-efficient in laser ablated germanium plasma

In the present experimental conditions, at Nd:YAG laser in fundamental (1064) nm, at laser irradiance 1.0 × 1011 Wcm−2 the (IB) absorption αib is approximately equal to (0.0204 cm-1). In present work irradiance is varied from 1.0 × 1011 to 1.8 × 1011Wcm−2 and inverse bremsstrahlung varies from 2.0 × 10−3 to 1.2 × 10−2 cm−1. The power absorbed by germanium target surface is found to be Pabs = 2.07 × 108 Wcm−2 and 1.04 × 103 Wcm−2 is reflected back from germanium surface. Whereas at highest laser irradiance 1.8 × 1011 Wcm−2 the power absorbed by surface is found to be Pabs = 3.67 × 108 Wcm−2 and 1.84 × 103Wcm−2 is reflected back from germanium surface. In present work we have calculated laser absorbance and percentage which is estimated by absorbed light throughout the original irradiance I0 at target surface, in present work absorbance at germanium surface is 0.2 where as reflectivity R of germanium sample which is found to be 0.39 for 1064 nm wavelength. At irradiance I0 1.0 × 1011 Wcm−2 the energy penetrated is E∼5.05 × 1010 Wcm−2 and for high laser irradiance at I0 1.8 × 1011 Wcm−2 the energy penetrated is E∼8.95 × 1010 Wcm−2 respectively.

Effect of powder feeding rate on heat and mass transfer behaviors during filler powder laser welding

The heat and mass transfer behavior is the influencing factor of welding quality, during filler powder laser welding. The characteristics of plasma and keyhole can characterize the heat and mass transfer behavior. Experimental platforms were built to observe the effect of powder feeding rate on the heat and mass transfer behavior. The main results of the experiment are as follows. In the process of filler powder laser welding, the keyhole depth and fusion depth were improved by selecting the critical value of powder feeding rate 5 g/min as the welding process parameter. When the powder feeding rate exceeded the critical value, the electron temperature and electron density decreased and increased respectively. The keyhole depth decreased with the increase of the inverse bremsstrahlung absorption coefficient of the keyhole plasma at the top of the keyhole. The keyhole area increased with the increase of plasma pressure at the keyhole opening. The inverse bremsstrahlung absorption of plasma plume and the number of powder particles sprayed into the molten pool were the factors that caused the decrease of the surface temperature and the length of the molten pool.

Emission Studies of Silicon Plasma Produced by a Nd: YAG Laser

In the present experimental work emission studies of silicon (Si) plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Nd: YAG laser are studied. The electron temperature measurements have been estimated using the Boltzmann plot method. The electron temperature as a function of laser irradiance (2 × 1010 to 6.5 × 1010 W/cm2) ranges from 11290 to 14120 K (for fundamental), and 11660 to 13750 K (for second) laser respectively. The electron number density is calculated using the Stark broadening profile of 288.15 nm (3p4s 1P1 → 3s 23p 2 1D2) transition. The electron number density as a function of laser irradiance ranges from 2.20 × 10 16 to 1.55 × 1017/cm3(for fundamental) and 1.09 × 1016 to 1.80 × 1017/cm3(for second) laser respectively. The spatial distribution of electron temperature and electron number density shows the same decreasing trend up to 2.0 mm from the target surface (0.05 mm). It is observed that electron temperature and number density increase as laser irradiance is increased. In addition the inverse bremsstrahlung absorption coefficient has been estimated. Variation of these plasma parameters (electron temperature and number density) along with variation of distances in the direction of propagation of the plasma plume have also been investigated.

The inverse bremsstrahlung absorption coefficients and Gaunt factors in astrophysical plasmas

In this paper we present the method of determination of the electron-ion inverse Bremsstrahlung characteristics in order to cover the corresponding stellar atmosphere models. The used method is based on cut-off Coulomb model potential. It is shown that determination of these characteristics i.e. the absorption coefficients and Gaunt factors can be successfully performed in the region of electron densities from 1013cm3 to 3 · 1019cm3 and temperatures from 3000 K to 50000 K within the wavelength region 100 nm ≤ λ ≤ 3000 nm.

Effect of high power CO2 and Yb:YAG laser radiation on the characteristics of TIG arc in atmospherical pressure argon and helium

Abstract The effects of laser radiation on the characteristics of the DC tungsten inert gas (TIG) arc were investigated by applying a high power slab CO 2 laser and a Yb:YAG disc laser. Experiment results reveal that the arc voltage–current curve shifts downwards, the arc column expands, and the arc temperature rises while the high power CO 2 laser beam vertically interacts with the TIG arc in argon. With the increase of the laser power, the voltage–current curve of the arc shifts downwards more significantly, and the closer the laser beam impingement on the arc to the cathode, the more the decrease in arc voltage. Moreover, the arc column expansion and the arc temperature rise occur mainly in the region between the laser beam incident position and the anode. However, the arc characteristics hardly change in the cases of the CO 2 laser–helium arc and YAG laser–arc interactions. The reason is that the inverse Bremsstrahlung absorption coefficients are greatly different due to the different electron densities of the argon and helium arcs and the different wave lengths of CO 2 and YAG lasers.

The influence of different volume ratios of He and Ar in shielding gas mixture on the power waste parameters for Nd:YAG and CO2 laser welding

In this paper, we numerically solve the Saha equations to drive the number densities of electrons and ions, the degrees of ionization of the plasma as well as the refractive indices and the inverse Bremsstrahlung absorption coefficients as a function of temperature for a variety of volume ratios of the (He+Ar) mixtures. Furthermore, the heat transfer equation was solved to determine the plasma temperature. The effect of shielding gas volume ratios on the power waste parameters was estimated during long pulse Nd:YAG and CW CO2 laser welding accompanying the experimental verification.

Determination of energy coupling to material in laser welding by a novel “sandwich” method

A mathematical energy coupling model was developed to analyze the light transmission in the keyhole and energy distribution on the keyhole wall. The main characteristics of the model include: 1) a prototype of the keyhole and the inverse Bremsstrahlung absorption coefficient in the keyhole plasma are obtained from the experiments; 2) instead of using a parallel incident beam, a focused laser beam with real Gaussian intensity distribution is implemented; 3) both Fresnel absorption and inverse Bremsstrahlung absorption during multiple reflections are considered. The calculation results show that the distribution of absorbed laser intensity by the keyhole wall is not uniform. The maximum laser energy is absorbed by the bottom of the keyhole, although no rays irradiate directly onto the bottom. According to analysis of beam focusing characteristics, the location of the focal plane plays a more important role in the laser energy absorption by the front wall than by the rear wall.

Distribution of the intensity absorbed by the keyhole wall in laser processing

The distribution of the energy flux absorbed by the wall is investigated after the laser beam undergoes multiple diffuse and specular reflections in a hemispherical cavity. The laser beam is characterized by different energy distribution parameter, wavelength, and polarization. Inverse Bremsstrahlung absorption within the plasma and Fresnel absorption on the cavity wall are taken into account. Scattering within the plasma, radiation absorption due to surface temperature and alternation of polarization in the process of multiple reflections are assumed to be negligible. The analytic model is derived and compared with the Monte Carlo method. The influences of wavelength, polarization, inverse Bremsstrahlung absorption coefficient and material property on the absorbed intensity are discussed.

The effects of the use of different shielding gas mixtures in laser welding of metals

The paper makes use of the solution of the system of Saha equations derived for any mixture of ionized monatomic gases. This solution is specifically applied to the case of two-component mixtures of the gases used as shields in the process of laser welding, namely Ar plus He, Ar plus O2, Ar plus N2 and Ar plus H2. The number densities of electrons and ions, the degrees of ionization of the plasma as well as the refractive indices and the inverse Bremsstrahlung absorption coefficients are presented as functions of temperature for a variety of volume ratios of the gases in the mixtures. The properties of the mixture of helium and argon change dramatically as the volume ratio of the two gases is altered. This mixture is also most interesting insofar as laser welding is concerned because it causes only very slight defocusing of the laser light above the keyhole.

Measurements of the heat flux, inverse bremsstrahlung absorption and equilibration in an under-dense laser heated plasma

A fully ionised hydrogen plasma of initial density approximately=5*1017 cm-3 and temperature approximately=12 eV is heated using a 1.053 mu m laser beam focussed to a spot of 200 mu m diameter with an irradiance of 5*1013 W cm-2. The resulting evolution of the plasma is monitored by Thomson scattering of a second laser beam at 5265 AA. Comparison with a one-dimensional two fluid hydrodynamic simulation shows that the inverse bremsstrahlung absorption coefficient should be modified to include the strong field correction and that the maximum heat flux is about 0.1 of the free streaming limit. The ratio of the electron mean free path to the temperature scale length is about 0.1 and Te/Ti approximately=5. The level of ion acoustic turbulence is observed to be small, close to thermal. The ion-electron equilibration rate is found to agree with the usual classical value.

Time resolved Thomson scattering measurements of the electron and ion temperatures in a high intensity laser–plasma interaction

Time resolved Thomson scattering from thermal plasma fluctuations is used to measure the electron and ion temperatures in the interaction of a short pulse (1 nsec FWHM), high intensity (∼2×1014 W/cm2) CO2 laser beam with a preformed carbon plasma. Time histories of the plasma temperatures with a temporal resolution of ∼150 psec were obtained in a single irradiation/discharge event by streaking the Thomson scattering spectrum. The experimentally measured electron temperature was found to be lower than that predicted by computer simulations. The discrepancy is attributed mainly to a decrease in the inverse bremsstrahlung absorption coefficient at high laser intensities (vosc/ve>1) .

Laser-Driven Detonation Waves in Gases

The plasma created by the output of a 2 to 10 J Q-switched ruby laser focused into air, argon, helium and hydrogen at pressures from 15 to 1000 psi has been photographically recorded during and after the laser heating pulse. The growth of the luminous plasma front during laser irradiation was in accordance with a prediction based on a radiatively supported detonation-wave model in which a Gaussian pulse shape was used for the instantaneous energy addition. With hydrogen at atmospheric pressure an appreciable fraction of the laser energy was transmitted. Consequently, the detonation-wave model had to include only partial absorption of the incident laser beam. This was done by using the inverse bremsstrahlung absorption coefficient and a constant depth of energy addition. The shock wave created by this sudden energy addition was observed by using a Schlieren system. The growth of the shock wave was not in accordance with that predicted by spherical-blast-wave theory. The shock-wave position from the initial point of breakdown varied as time from breakdown to the (0.20 ± 20%) power independent of gas species or operating condition.