A large laser spark was produced in a homogeneous sulphur hexafluoride gas (pressures ranged from 10.7 to 101.3 kPa) by a focused high-power laser pulse (350 ps, 125 J, 1315.2 nm). Magnetic fields, electromagnetic pulses (EMPs), optical emission spectra (OES) and chemical changes associated with the laser-induced dielectric breakdown (LIDB) in the SF6 gas were investigated. During the laser interaction, hot electrons escaping the plasma kernel produced EMPs and spontaneous magnetic fields, the frequency spectrum of which contains three bands around 1.15, 2.1 and 3 GHz, while the EMP frequency band appeared around 1.1 GHz. The EMP emission from a laser spark was very weak in comparison to those generated at a solid target. Gas chromatography revealed the formation of only a limited number of products and a low degree of sulphur hexafluoride (SF6) conversion. OES diagnosed the LIDB plasma in the phase of its formation as well as during its recombination.

The swelling properties of smectite-type clay particles (including montmorillonite) are of interest in various industries. A fundamental understanding of the surface properties of smectite particles at the sub-micron level would facilitate investigation of the effect of distributed properties such as charge and elemental composition. Swelling and delamination of SWy-2 Na-montmorillonite (Na-Mnt) nano-clay particles were studied here using size distributions obtained by sedimentation field-flow fractionation (SdFFF). Fractions were examined by electron microscopy and inductively-coupled optical emission spectroscopy (ICP-OES). Two distinct populations were observed in the size distribution of SWy-2 Na-Mnt particles (bimodal size distribution), with mean equivalent spherical diameters of ~60 nm and 250 nm, respectively. In contrast, the size distribution of STx-1 Ca-montmorillonite (Ca-Mnt) particles showed only one peak with a mean equivalent spherical diameter of ~410 nm, which changed to 440 nm after 4 days of hydration. Analyses of the fractions by ICP-OES obtained along the size distribution of Na-Mnt showed an abundance of Ca and Mg in the fractions below 250 nm, and confirmed the presence of Fe and Mg as isomorphous substituents. Electron micrographs of the fractions obtained from Na-Mnt size distributions were used to calculate the thickness of the clay particles. Bridging forces between pure orMgsubstituted montmorillonite and either Ca2+ or Na+ were calculated using semi-empirical methods. The results demonstrated that swelling and delamination of Na-Mnt clay particles are dictated by properties such as elemental composition and surface charge which are distributed along the size distribution.

We investigated the expansion dynamics of laser-produced plasmas expanding into an axial magnetic field. Plasmas were generated by focusing 1.064 μm Nd:YAG laser pulses onto a planar tin target in vacuum and allowed to expand into a 0.5 T magnetic field where the field lines were aligned along the plume expansion direction. Gated images employing an intensified charge-coupled device showed focusing of the plasma plume, which were also compared with results, obtained using particle-in-cell modeling methods. The estimated density and temperature of the plasma plumes employing emission spectroscopy revealed significant changes in the presence and absence of the 0.5 T magnetic field. In the presence of the field, the electron temperature is increased with distance from the target, while the density showed opposite effects.

The surface flashover behavior in ambient air and nitrogen are studied at a pressure of 1 kg/cm2 using optical emission spectroscopy. A high dc voltage is applied to Rogowski profile electrodes with polyoxymethylene as the insulator between the electrodes. Three different conditions of needle protrusion along the surface of polyoxymethylene are used to study the variation in spectral characteristics due to particle contamination. When the insulator is placed between the spark gap electrodes, the OES spectra are dominated by the Hα line in air and nitrogen medium. It was found that the intensity of N2+ (B-X) emission is less in air surrounding the insulator medium. The plasma temperature during bulk breakdown in air is 0.433 eV, which increases to 0.434 eV with the pressurized nitrogen, which further increases in the presence of insulator to 0.441 eV and 0.44 eV in nitrogen and air, respectively. The electron density is obtained from the N emission line at 746.8 nm and the estimated peak value is 2.85 × 1012 cm−3 in the presence of insulator. The plasma temperature decreases with increase in distance of particle contamination from cathode. The increase in electron density in air, as compared to nitrogen implies more material desorption in air which is also supported by the comparisons of Hα lines.

In this work, we present the spectroscopic studies of the plasma generated at the surface of manganese sulfate by the fundamental (1064 nm) and second harmonic (532 nm) of a Q-switched Nd:YAG laser. The 4s4p 4F7/2→ 4s 2H9/2 at 438.80 nm, 4p 2I11/2 → 4s22I11/2 at 440.80 nm, 4p 4G11/2 → 4s 2H9/2 at 464.27 nm, 4p 4F5/2→ 4s 4D7/2 at 467.16, 4p 4F5/2 → 4s24G 7/2 at 515.08 nm, and 4p 4F7/2 → 4s2 4G 9/2 at 519.65 nm transitions have been used to estimate the electron temperature through the Boltzmann plot method. The number density has been estimated from the Stark broadened profiles of the spectral line 348.30 nm. The spatial behavior of the electron temperature and number density has been examined at different ambient air pressures and with laser irradiance. The temperature and number density are found to be in the range from 9842 K to 9371 K and 1.58 × 1017 to 3.26 × 1016 cm−3 for the 1064 nm laser, from 9668 to 9297 K and 2.27 × 1017 to 5.79 × 1016 cm−3 for the 532 nm laser.

In this paper, measurement of various plasma parameters during pulsed laser deposition of ZnO thin films on Si (100) substrates is reported. The variations of electron number density and electron temperature with ambient pressure and target substrate distance is obtained via spectroscopic measurements. The structural and optical properties of ZnO thin films were analyzed using X-ray diffraction, scanning electron microscope, and photoluminescence and then correlated with spectroscopic results to find optimum conditions for the deposition of high quality ZnO thin films.