Two-color laser scattering for diagnostics of hydrogen plasma

A two-color laser scattering (2CLS) method is proposed to measure electron and neutral densities, as well as electron and ion temperatures in hydrogen plasma. 2CLS uses two probe wavelengths to identify the Rayleigh scattering and Thomson scattering contributions coming from neutrals and electrons, respectively. Laser scattering signals were simulated for various conditions of a hydrogen plasma at thermodynamic equilibrium applying the available and calculated cross-sections for Rayleigh scattering by ground-sate and excited hydrogen atoms at probe wavelengths of 355 nm and 532 nm. The developed 2CLS method was eventually applied to study the laser-induced plasma in hydrogen at near atmospheric pressure. Temporally and spatially resolved electron and ion temperatures and densities of electrons and hydrogen atoms (ground-state and excited) were determined

What can we learn about laser-induced plasmas from Thomson scattering experiments

This article describes laser Thomson scattering as applied to investigate laser-induced plasmas originating from gas breakdown or ablation of solid samples. Thomson scattering provides a reliable and direct mean of determining plasma electron density and electron temperature with high spatial and temporal resolution. Moreover, unlike e.g. optical emission spectroscopy, no assumptions about axial symmetry, thermodynamic conditions in the plasma or its chemical composition are needed to quantify these fundamental plasma parameters. Because Thomson scattering is inherently accompanied by Rayleigh light scattering, information about concentration of heavy particles and their temperature can be simultaneously derived from the experimental data. The heavy particle temperature and the electron one are the primary indicators of the plasma thermodynamic equilibrium. The goals of this article are to describe the theory of Thomson scattering relevant for the studies of low-temperature laser-induced plasmas, discuss the instrumental details of Thomson scattering experiments, and review the results of studies in which this technique has been used to characterize laser-induced plasmas

Laser spectroscopy of thermal plasma

Thermal plasma, due to its applications, is a research field of great importance, but reliable diagnostics of such plasma remains a challenging task. Spatially resolved methods, which provide local values of plasma parameters, are crucial for understanding the underlying physics. This can be achieved using pump–probe techniques. Two methods applicable and useful for thermal plasma diagnostics—four-wave mixing and scattering of laser beams—are discussed in this paper. Experimental examples of their application, namely four-wave mixing in argon arc plasma and scattering of laser light by laser-induced plasma, are presented

Experimental investigations of plasma perturbation in Thomson scattering applied to thermal plasma diagnostics

International audienceTime and space resolved measurements of Thomson scattering of 532 nm, 6 ns laser pulses were performed on argon thermal discharge plasma with electron temperature Te10 000 K and electron density 8x1022 m−3ne21023 m−3. From these measurements, variations of the electron density and temperature across the laser beam and their evolution during the laser pulse were determined. While the electron density is augmented by no more than a few percent the electron temperature is significantly increased along the axis of the laser beam due to laser heating. It is also shown that the higher initial electron density, the more disturbed is the plasma. The initial “undisturbed” electron density was derived by studying the spatial variations of ne within the laser beam. On the other hand, the initial electron temperature was determined by studying the temporal evolution of Te during the laser pulse and then by extrapolating the results to the origin of the pulse. Despite strong and nonlinear plasma heating by the Thomson scattered laser light, our study yields temperatures close to those obtained by modeling and time-resolved spectroscopic measurements

Structural and Optical Properties of Pure and Sulfur-Doped Silicate–Phosphate Glass

A series of silicate–phosphate glass materials from the SiO2-P2O5-K2O-MgO system (pure and doped with sulfur ions) were synthesized by melting raw material mixtures that contained activated carbon as a reducer. The bulk composition of glass was confirmed with X-ray fluorescence spectroscopy. The homogeneity of the glass was confirmed through elemental mapping at the microstructural level with scanning electron microscopy combined with an analysis of the microregions with energy-dispersive X-ray spectroscopy. The structural and optical properties of the glass were studied by using spectroscopic techniques. The infrared spectroscopy studies that were conducted showed that the addition of sulfur caused changes in the silicate–phosphate networks, as they became more polymerized, which was likely related to the accumulation of potassium near the sulfur ions. By using irradiation with an optical parametric oscillator (OPO) nanosecond laser system operating at the second harmonic wavelength, the glass samples emitted a wide spectrum of luminescence, peaking at about 700 nm when excited by UV light (210–280 nm). The influence of the glass composition and the laser-processing parameters on the emission characteristics is presented and discussed. This work also referred to the density, molar volume, and theoretical optical basicity of pure and sulfur-doped glass

Simultaneous measurement of electron and heavy particle temperatures in He laser-induced plasma by Thomson and Rayleigh scattering

Thomson and Rayleigh scattering methods were applied to quantify the electron and heavy particle temperatures, as well as electron number density, in a laser spark in helium at atmospheric pressure. Plasma was created using 4.5 ns, 25 mJ pulses from Nd:YAG laser at 532 nm. Measurements, performed for the time interval between 20 ns and 800 ns after breakdown, show electron density and temperature to decrease from $7.8 \times 10^{23}m^{-3}$ to $2.6 \times 10^{22}m^{-3}$ and from 95 900 K to 10 350 K, respectively. At the same time, the heavy particle temperature drops from only 47 000 K down to 4100 K which indicates a two temperature plasma out of local isothermal equilibrium

Investigation of the local thermodynamic equilibrium of laser-induced aluminum plasma by Thomson scattering technique

A laser Thomson scattering method was applied to investigate the local Saha–Boltzmann equilibrium in aluminum laser-induced plasma. Plasma was created in ambient air using 4.5 ns pulses from a Nd:YAG laser at 532 nm, focused on an Al target. Spatially resolved measurements, performed for the time interval between 600 ns and 3 μs, show electron density and temperature to decrease from 3.4 × 1023 m− 3 to 0.5 × 1023 m− 3 and from 61,000 K to 13,000 K in the plasma core. The existence of local thermodynamic equilibria in the plasma was verified by comparing the rates of the collisional to radiative processes (the McWhirter criterion), as well as relaxation times and diffusion lengths of different plasma species, with the appropriate rate of electron density evolution and its gradients at given, experimentally determined, electron temperatures. We found these criteria to be much easier to satisfy for metallic plasma species than for nitrogen. The criteria are also easier to satisfy in the plasma core of higher electron density