Milos Momcilovic

The effect of potassium addition on plasma parameters in argon dc plasma arc

The effect of potassium addition on the radial distribution of temperature and electron number density in a U-shaped direct current (dc) argon plasma operating at different arc currents has been studied by optical emission spectroscopic techniques and the power interruption method. Spatially resolved electron number densities (ne) have been determined from measured radial profiles of Balmer-Hβ spectral line. The obtained electron number densities have been used for thermodynamic temperature (TLTE) evaluation with the assumption that the arc plasma is in a state of local thermodynamic equilibrium. The excitation temperatures (Texc) have been determined from the absolute integral emissivity of the argon line at 430.01 nm. For heavy particle temperature (Th) evaluations we have used a power interruption method. The obtained results have shown that an addition of KCl decreases both electron number density and temperature of the arc column. The magnitude of such an influence on plasma parameters increases with an increase in the KCl concentration and decreases with an increase in the arc current.

Optical Emission Studies of Copper Plasma Induced Using Infrared Transversely Excited Atmospheric (IR TEA) Carbon Dioxide Laser Pulses

Spatially resolved, time-integrated optical emission spectroscopy was applied for investigation of copper plasma produced by a nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 μm. The effect of surrounding air pressure, in the pressure range 0.1 to 1013 mbar, on plasma formation and its characteristics was investigated. A linear dependence of intensity threshold for plasma formation on logarithm of air pressure was found. Lowering of the air pressure reduces the extent of gas breakdown, enabling better laser-target coupling and thus increases ablation. Optimum air pressure for target plasma formation was 0.1 mbar. Under that pressure, the induced plasma consisted of two clearly distinguished and spatially separated regions. The maximum intensity of emission, with sharp and well-resolved spectral lines and negligibly low background emission, was obtained from a plasma zone 8 mm from the target surface. The estimated excitation temperature in this zone was around 7000 K. The favorable signal to background ratio obtained in this plasma region indicates possible analytical application of TEA CO2 laser produced copper plasma. Detection limits of trace elements present in the Cu sample were on the order of 10 ppm (parts per million). Time-resolved measurements of spatially selected plasma zones were used to find a correlation between the observed spatial position and time delay. Index Headings: Laser induced Cu-plasma emission; Shock wave plasma; Copper target; Transversely excited atmospheric CO2 laser; TEA CO2 laser.

Analytical capability of the plasma induced by IR TEA CO 2 laser pulses on copper-based alloys

The applicability of a nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 µm and 100 ns pulse length (initial spike), induced plasma under reduced air pressure for spectrochemical analysis of bronze and brass samples was investigated. The plasma consisted of two clearly distinguished and spatially separated regions and expanded to a distance of about 10 mm from the surface. The elemental composition of the samples was determined using a time-integrated space-resolved laser-induced plasma spectroscopic (TISR-LIPS) technique. Sharp and well-resolved spectral lines mostly atomic, and negligibly low background emission, were obtained from a plasma region 7 mm from the target surface. Good signal to background and signal to noise ratios were obtained. The estimated detection limits for the trace elements Mg, Fe, Al and Ca were in the order of 10 ppm in bronze and around 50 ppm in brass. Damage on the investigated samples induced by TEA CO2 laser radiation was negligible.

Laser-Induced Breakdown Spectroscopy (LIBS): specific applications

A short overview of Laser Induced Breakdown Spectroscopy (LIBS) with emphasis on the new trends is presented. Nowadays, due to unique features of this technique, LIBS has found applications in a great variety of fields. Achievements in the application of LIBS in nuclear area, for hazardous materials detection and in geology were considered. Also, some results recently obtained at VINCA Institute, with LIBS system based on transversely excited atmospheric (TEA) CO2 laser, are presented. Future investigations of LIBS will be oriented toward further improvement of the analytical performance of this technique, as well as on finding new application fields.

Properties of plasma induced by pulsed CO2 laser on a copper target under different ambient conditions

Optical emission spectroscopy was applied for investigation of copper plasma induced by a nanosecond transversely excited atmospheric CO2 laser, operating at 10.6 μm. The effect of the background gas (air, Ar, He and N2) and pressure (1–25 mbar) on plasma formation was examined. The plasma shielding effect was more pronounced for background gases with lower ionization potential than for He. The increase of He pressure from 1 to 25 mbar resulted in fivefold increase of Cu atomic line intensity.

Pulsed TEA CO2 Laser Irradiation of Titanium in Nitrogen and Carbon Dioxide Gases

Surface changes created by interaction of transversely excited atmospheric carbon dioxide (TEA CO2) laser with titanium target/implant in nitrogen and carbon dioxide gas were studied. TEA CO2 laser operated at 10.6 μm, pulse length of 100 ns and fluence of ∼17 J/cm2 which was sufficient for inducing surface modifications. Induced changes depend on the gas used. In both gases the grain structure was produced (central irradiated zone) but its forms were diverse, (N2: irregular shape; CO2: hill-like forms). Hydrodynamic features at peripheral zone, like resolidified droplets, were recorded only in CO2 gas. Elemental analysis of the titanium target surface indicated that under a nitrogen atmosphere surface nitridation occurred. In addition, irradiation in both gases was followed by appearance of plasma in front of the target. The existence of plasma indicates relatively high temperatures created above the target surface offering a sterilizing effect.

LIBS Analysis of Geomaterials: Comparative Study of Basalt Plasma Induced by TEA CO2 and Nd:YAG Laser in Air at Atmospheric Pressure

We present a study of the plasma generated by transversely excited atmospheric (TEA) CO2 laser irradiation of a basalt sample. The plasma was induced in air at atmospheric pressure. The same sample was also analyzed using a commercial LIBS system based on Nd:YAG laser and time-gated detection. The main plasma parameters, temperature, and electron number density were determined and analytical capabilities of the two systems compared. Despite differences in laser wavelength, pulse duration, applied fluence, and signal detection scheme, the two systems are comparable in terms of element detectability and limits of detection. In both cases, all elements usually present in geological samples were identified. The estimated limits of detection for most elements were below 100 ppm, while for Cu, Cr, and Sr they were around or below 10 ppm. The obtained results led to the conclusion that simple, cost-effective TEA CO2 LIBS system can find applications for geological explorations.