SIGNAL ENHANCEMENT; LIBS; DEPENDENCE; SOIL; MICROANALYSIS; EMISSION; ABLATION; LIQUIDS

Laser-induced breakdown spectroscopy (LIBS) is a technique increasingly used to perform fast semi-quantitative multi-elemental analyses of various materials without any complex sample preparation, being also suitable for in situ analyses. Few studies have been performed to understand the influence of laserwavelength on LIBS analytical performance on environmental samples. The main goal of this study was to perform a comparative elemental analysis of a number of soils, citrus leaves, and synthetic solid matrices using two different wavelengths, i.e., 532 and 1064 nm of Nd: YAG lasers, and a spectrometer coupled to a non-intensified charge-coupled device camera as the detection system. The emission lines with higher upper energy level, i.e., C I-193.03 (7.685 eV) and Si I-212.41 nm (6.616 eV), were more intense when using the 532 nm than the 1064 nm laser light, whereas the opposite occurred for elements with lower upper energy level, i.e., Ti I-336.12 nm (3.716 eV) and Fe I-368.75 nm (4.220 eV). The observed increase in LIBS signal between the two wavelengths is about 30-50%. The relationship between the line emission intensities and the used excitation wavelengths were associated to the upper level energy of the element.

PRE-ABLATION SPARK; ORTHOGONAL BEAM GEOMETRY; INDUCED PLASMAS; CONFIGURATION; SPECTROMETRY; EMISSION; MATRICES; SINGLE; LIBS

Two Q-switched Nd: YAG lasers at 1064-nm wavelength have been employed to detect the trace elements in microalloy steel samples by single-pulse and reheating double-pulse laser-induced breakdown spectroscopy. It is found that the emission lines intensities of the trace elements were significantly enhanced by reheating double-pulse scheme. Furthermore, the extent of the enhancement of the line intensity was related to the excitation energy level of the emission line. Then, the emission enhancement was explained by the investigation of the spatial resolution of the plasma temperatures. The results have shown that the enhancement mechanism can be attributed to the greater and hotter plasma generated by the re-excitation of the reheating laser pulse in double-pulse scheme. Finally, calibration plots were constructed for Mn, Cr, and Cu using a set of certified microalloy steel samples. The detection limits of the trace elements were calculated for the reheating double-pulse scheme and compared to those of single-pulse scheme. It has been shown that the detection limits of the trace elements were improved by a factor of 1.81-3.46 when the reheating double-pulse scheme was used.

INDUCED BREAKDOWN SPECTROSCOPY; TIME; EQUILIBRIUM; PARAMETERS; DEPOSITION; DENSITY; SPACE; NDYAG; GAS; CO2

The magnesium plasma induced by a 1064-nm Q-switched Nd: YAG laser in atmospheric air was investigated. The evolution of the plasma was studied by acquiring spectral images at different laser energies and delay times. We observed that the intensities of the spectral lines decrease with larger delay times. The electron temperature was determined using the Boltzmann plot method. At a delay time of 100 ns and laser energy of 350 mJ, the electron temperature attained their highest value at 10164 K and then decreases slowly up to 8833.6 K at 500 ns. We found that the electron temperature of the magnesium plasma increases rapidly with increasing laser energy.

INDUCED BREAKDOWN SPECTROSCOPY; COMBUSTION CHEMISTRY; POTASSIUM RELEASE; IDENTIFICATION; PRESSURE

Laser-induced breakdown spectroscopy (LIBS) technique is used to record some plasma emissions of different laminar diffusion methanol, ethanol, and n-propanol alcohol flames, to investigate the shapes, structures (i.e., reactants and products zones), kind, and quality of burning in different areas. For this purpose, molecular bands of CH, CH*, C-2, CN, and CO as well as atomic and ionic lines of C, H, N, and O are identified, simultaneously. Experimental results indicate that the CN and C-2 emissions have highest intensity in LIBS spectrum of n-propanol flame and the lowest in methanol. In addition, lowest content of CO pollution and better quality of burning process in n-propanol fuel flame toward ethanol and methanol are confirmed by comparison between their CO molecular band intensities. Moreover, variation of the signal intensity from these three flames with that from a known area of burner plate is compared. Our findings in this research advance the prior results in time-integrated LIBS combustion application and suggesting that LIBS can be used successfully with the CCD detector as a non-gated analytical tool, given its simple instrumentation needs, real-time capability applications of molecular detection in laminar diffusion flame samples, requirements.

NONLINEAR OPTICS; FILAMENTATION; AIR; OPERATION; PULSES; WATER; GAS

We extend the detection range of laser-induced breakdown spectroscopy by combining high-intensity femtosecond laser pulses with high-energy nanosecond - CO2 laser pulses. The femtosecond laser pulses ionize the molecules and generate filament in air. The free electrons generated in the self-confined plasma channel by the femtosecond laser serve as the seed electrons which cause efficient avalanche ionization in the nanosecond - CO2 laser field. We show that the detection distance has been extended by three times with the assistance of femtosecond laser filamentation.

INDUCED BREAKDOWN SPECTROSCOPY; SINGLY IONIZED ALUMINUM; DUAL PULSE EXCITATION; EXPANSION DYNAMICS; ELEMENTAL ANALYSIS; ABLATION PLUME; GENERATION; EMISSION; UNDERWATER; LIQUID

We report on the findings of double-pulse studies performed on an aluminium target submerged in water using Nd: YAG laser pulses. Shadowgraphy measurements were performed to examine the dynamic behaviour of the cavitation bubble that eventually forms some considerable time post-plasma ignition. These measurements were used to inform subsequent investigations designed to probe the bubble environment. The results of time-resolved imaging from within the cavitation bubble following irradiation by a second laser pulse reveal the full dynamic evolution of a plasma formed in such an environment. Rapid displacement of the plasma plume in a direction normal to the target surface followed by a diffusive outwards expansion is observed and a qualitative model is proposed to explain the observed behaviour. Line profiles of several ionic and atomic species were observed within the irradiated cavitation bubble. Electron densities were determined using the Stark broadening of the Al II line at 466.3 nm and electron temperatures inferred using the ratio of the Al II (466.3 nm) and Al I (396.15 nm) lines. Evidence of self-reversal of neutral emission lines was observed at times corresponding to growth and collapse phases of the cavitation bubble suggesting high population density for ground state atoms during these times.