DOI: 10.1063/1.4986027

Authors
Chen, A. M. ; Jiang, Y. F. ; Jin, M. X. ; Ke, D. ; Li, S. Y. ; Sui, L. Z. ; Wang, Y. ; Zhang, D.

Keywords

INDUCED BREAKDOWN SPECTROSCOPY; DOUBLE-PULSE; OPTICAL-EMISSION; CAVITY CONFINEMENT; TEMPERATURE; IMPROVEMENT; SILICON

Abstract

The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 mu s when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave. Published by AIP Publishing.

DOI: 10.1063/1.4973554

Authors
Mortazavi, S. Z. ; Parvin, P. ; Reyhani, A.

Keywords

INDUCED BREAKDOWN SPECTROSCOPY; Q-SWITCHED NDYAG; METHANE DECOMPOSITION; ATMOSPHERIC-PRESSURE; ELECTRON-DENSITY; DEHYDROGENATION; HYDROGEN; DISSOCIATION; TEMPERATURE; CATALYSTS

Abstract

It is shown that the propane molecules are strongly decomposed in the metal assisted laser induced plasma based on the nano-catalytic adsorption. A Q-Switched Nd:YAG laser is employed to irradiate the propane gas filled in the control chamber in the presence of the reactive metals such as Ni, Fe, Pd, and Cu in order to study the effect of catalysts during the decomposition. The catalytic targets simultaneously facilitate the plasma formation and the decomposition events leading to generate a wide distribution of the light and heavy hydrocarbon molecules, mainly due to the recombination processes. Fourier transform infrared spectroscopy and gas chromatography instruments support the findings by detecting the synthetic components. Furthermore, the optical emission spectroscopy of the laser induced plasma emissions realizes the real time monitoring of the reactions taking place during each laser shot. The subsequent recombination events give rise to the generation of a variety of the hydrocarbon molecules. The dissociation rate, conversion ratio, selectivity, and yield as well as the performance factor arise mainly from the catalytic effects of the metal species. Moreover, the ablation rate of the targets of interest is taken into account as a measure of the catalytic reactivity due to the abundance of the metal species ablated from the target. This leads to assess the better performance factor for Pd among four metal catalysts of interest during propane decomposition. Finally, the molecules such as ethane and ethylene are identified as the stable abundant species created during the successive molecular recombination processes. Published by AIP Publishing.

DOI: 10.1063/1.4973658

Authors
Chen, A. M. ; Jiang, Y. F. ; Sui, L. Z. ; Tian, D. ; Wang, X. W. ; Zhang, D.

Keywords

Q-SWITCHED NDYAG; EMISSION ENHANCEMENT; OPTICAL-EMISSION; PLASMA; SPARK

Abstract

In this study, we observed the evolution of the spectral emission intensity of a glass sample with the increase of sample temperature, laser energy, and delay time in femtosecond laser-induced breakdown spectroscopy (fs-LIBS). In the experiment, the sample was uniformly heated from 22 degrees C to 200 degrees C, the laser energy was changed from 0.3 mJ to 1.8 mJ, and the delay time was adjusted from 0.6 mu s to 3.0 mu s. The results indicated that increasing the sample temperature could enhance the emission intensity and reduce the limits of detection, which is attributed to the increase in the ablated mass and the plasma temperature. And the spectral intensity increases with the increase of the laser energy and the delay time, however, the spectral line intensity no longer increases when the laser pulse energy and delay time reach a certain value. This study will lead to a further improvement in the applications of fs-LIBS. Published by AIP Publishing.

DOI: 10.1063/1.4973444

Authors
Costello, J. T. ; Fiedorowicz, H. ; Kelly, T. J.

Keywords

INDUCED BREAKDOWN SPECTROSCOPY; POLARIZATION SPECTROSCOPY

Abstract

The polarisation anisotropy of the emission from a laser produced aluminium plasma has been studied using time and polarisation resolved spectroscopy at various background pressures of air. A Wollaston prism was used to resolve the emission from the plasma into polarisation components that are parallel and orthogonal to the plasma expansion axis. Spectroscopy reveals that as the background pressure is increased, strongly polarised continuum emission dominates at early stages of the plasma formation. The results are compared and contrasted to similar experiments and discussed in the framework of a recombining plasma. Published by AIP Publishing.

DOI: 10.1063/1.4985678

Authors
Brumfield, B. E. ; Miloshevsky, A. ; Miloshevsky, G. ; Phillips, M. C. ; Skrodzki, P. J.

Keywords

PRECURSOR IONIZATION; TEMPORAL EVOLUTION; AMBIENT CONDITIONS; ENERGY-ABSORPTION; SHOCK-WAVE; AIR; SPECTROSCOPY; SPARK; ARGON; ABLATION

Abstract

Laser-heated gas breakdown plasmas or sparks emit profoundly in the ultraviolet and visible region of the electromagnetic spectrum with contributions from ionic, atomic, and molecular species. Laser created kernels expand into a cold ambient with high velocities during their early lifetime followed by confinement of the plasma kernel and eventually collapse. However, the plasma kernels produced during laser breakdown of gases are also capable of exciting and ionizing the surrounding ambient medium. Two mechanisms can be responsible for excitation and ionization of the surrounding ambient: photoexcitation and ionization by intense ultraviolet emission from the sparks produced during the early times of their creation and/or heating by strong shocks generated by the kernel during its expansion into the ambient. In this study, an investigation is made on the spectral features of on-and off-axis emission of laser-inducedplasma breakdown kernels generated in atmospheric pressure conditions with an aim to elucidate the mechanisms leading to ambient excitation and emission. Pulses from an Nd:YAG laser emitting at 1064 nm with a pulse duration of 6 ns are used to generate plasma kernels. Laser sparks were generated in air, argon, and helium gases to provide different physical properties of expansion dynamics and plasma chemistry considering the differences in laserabsorption properties, mass density, and speciation. Point shadowgraphy and time-resolved imaging were used to evaluate the shock wave and spark self-emission morphology at early and late times, while space and time resolved spectroscopy is used for evaluating the emission features and for inferring plasma physical conditions at on- and off-axis positions. The structure and dynamics of the plasma kernel obtained using imaging techniques are also compared to numerical simulations using the computational fluid dynamics code. The emission from the kernel showed that spectral features from ions, atoms, and molecules are separated in time with early time temperatures and densities in excess of 35 000 K and 4 x 10(18)/cm(3) with an existence of thermal equilibrium. However, the emission from the off-kernel positions from the breakdown plasmas showed enhanced ultraviolet radiation with the presence of N-2 bands and is represented by non-local thermodynamic equilibrium (non-LTE) conditions. Our results also highlight that the ultraviolet radiation emitted during the early time of spark evolution is the predominant source of the photo-excitation of the surrounding medium. Published by AIP Publishing.

DOI: 10.1063/1.4985327

Authors
Aisha, G. ; Haq, S. U. ; Nadeem, A.

Keywords

INDUCED PLASMA SPECTROSCOPY; SELF-ABSORPTION; ACCURACY

Abstract

The quantitative analysis of the standard aluminum-silicon alloy has been performed using calibration free laser induced breakdown spectroscopy (CF-LIBS). The plasma was produced using the fundamental harmonic (1064 nm) of the Nd: YAG laser and the emission spectra were recorded at 3.5 mu s detector gate delay. The qualitative analysis of the emission spectra confirms the presence of Mg, Al, Si, Ti, Mn, Fe, Ni, Cu, Zn, Sn, and Pb in the alloy. The background subtracted and self-absorption corrected emission spectra were used for the estimation of plasma temperature as 10 100 +/- 300 K. The plasma temperature and self-absorption corrected emission lines of each element have been used for the determination of concentration of each species present in the alloy. The use of corrected emission intensities and accurate evaluation of plasma temperature yield reliable quantitative analysis up to a maximum 2.2% deviation from reference sample concentration. Published by AIP Publishing.