449 research outputs found
Quantitative chemical analysis of submerged solids using calibration-free laser-induced breakdown spectroscopy
No full textCavity formation and material ablation for single-pulse laser-ablated solids immersed in water at high pressure
No full textThe effects of hydrostatic pressure on cavity formation and material ablation have been investigated for a brass plate immersed in water irradiated by a single laser pulse of duration <10 ns. Shadowgraph imaging and volumetric measurements of the ablated material demonstrate that the density of the material inside the cavity does not vary significantly for hydrostatic pressures between 0.1 and 30 MPa (300 atm) during the early stages, <600 ns after laser irradiation, indicating that the pressures induced by focusing a high-power laser in the confined medium dominate the transient pressure regime over this period
Calibration-free analysis of immersed brass alloys using long-ns-duration pulse laser-induced breakdown spectroscopy with and without correction for nonstoichiometric ablation
No full textLong-ns-duration, single pulse laser-induced breakdown spectroscopy (LIBS) is known to be an effective method to observe well resolved spectra from samples immersed in water at high hydrostatic pressures. The aim of this study is to investigate whether the signals obtained using this method are suitable for quantitative analysis of chemical composition. Six certified brass alloys consisting of copper (Cu), zinc (Zn) and lead (Pb) were measured underwater using a laser pulse of duration 250 ns, and their compositions were determined using calibration-free LIBS (CF-LIBS) and corrected CF-LIBS (CCF-LIBS) methods. The mass fractions of Cu and Zn calculated using CF-LIBS showed better agreement with the certified values than those determined using CCF-LIBS, with relative errors of Cu 4.2 ± 3.3 % and Zn 7.2 ± 6.4 %. From the results, it can be said that the difference of preferential evaporation and ablation among elements does not need to be considered for underwater measurements with the long-pulse LIBS setup used in this work. While the results indicate that the CF-LIBS method can be applied for in situ quantitative analysis of major elements with concentrations > ~ 10 %, the mass fractions determined for Pb, with concentrations < 5 % had large relative errors, suggesting that an alternative method is required to quantify minor elements
Field emission of ZnO nano-structures produced by laser ablation
No full textThe thesis describes the development of, and results from, two new laboratory facilities designed to investigate the properties of laser produced plasmas, with in-situ time of flight mass spectrometry, for deposition of ZnO
materials for applications as field electron emission sources.
The results from the work are concerned with the study of the important physical processes present in a laser ablation zinc oxide plasma plume expanding into vacuum and various ambient gas pressures. The thesis also demonstrated the advantages of combining a linear ToF detector and a mass resolved ReToF spectrometer for clarification of ionisation processes in the pulsed laser ablation regime of solid targets. The outstanding results show that during the ablation process, ZnO atomises into Zn and O. In the vacuum regime we have shown that at long distances from the target
multiple charged states of Zn and O are present. While under the same conditions in an ambient gas the multiple charged states are not present, however the ambient gas undergoes an ionisation process.
Deposited materials are tested for applications as field electron emission sources, for analysis of field enhancement factors from nano-material ZnO
Towards real -time quantification of seawater composition using laser induced breakdown spectroscopy
No full textA study of laser-induced breakdown spectroscopy for analysis of the composition of solids submerged at oceanic pressures
No full textThe application of laser-induced breakdown spectroscopy for analysis of the chemical composition of solids immersed in water at oceanic pressures has been investigated. Well defined emission spectra were observed from plumes generated from underwater solids after excitation using a single laser pulse of duration less than 10 ns. It is demonstrated that an increase in water pressure from 0.1 to 30MPa (300 atm) does not have a significant effect on the intensity and broadness of the observed spectral lines. Shadowgraph images demonstrate that even at pressures of 30MPa, beyond the critical pressure of water, cavitation occurs around the ablated region. Furthermore, it is demonstrated that during the early stages, less than 1 s, after irradiation the size of the cavity is largely independent of the external fluid pressure for pressures up to 30MPa. It is suggested that the high pressure shock wave induced by the focused laser dominates the local pressure regime for close to 1 s after irradiation and generates a transient low pressure region in which a cavity can form for the plume to expand into. Measurements of craters formed in the solids after ablation at different pressures demonstrate that the amount of material ablated by the laser stays within the same order for all hydrostatic pressures tested. The results of this study suggest that laser-induced breakdown spectroscopy is, in principle, a technique suitable for in situ elemental analysis of both shallow water sediments and deep sea minerals.</p
Temperature based segmentation for spectral data of laser-induced plasmas for quantitative compositional analysis of brass alloys submerged in water
No full textThis study describes a method to quantify the composition of brass alloys submerged in water using laser-induced plasmas. Principal component regression (PCR) analysis and partial least squares (PLS) regression analysis are applied to spectral measurements of plasmas generated using a long-ns duration pulse. The non-linear effects of excitation temperature fluctuations on the signals are treated as systematic errors in the analysis. The effect of these errors on the analytical performance is evaluated by applying PCR and PLS with a temperature segmented database. The results of the analysis are compared to conventional methods that do not consider the excitation temperature and it is demonstrated that the proposed database segmentation improves accuracy, with root-mean square errors of prediction (RMSEP) of 2.7% and 2.8% for Cu and Zn in the PCR model and 2.9% and 1.8% for Cu and Zn in the PLS model, respectively. The results indicate that systematic effects contribute to fluctuation of underwater plasmas, where appropriate database segmentation can improve the performance of the PCR and PLS methods
Effect of laser fluence on atomic density ratio in the plasma produced by ns laser ablation on a Cu-Zn alloy
No full textUnderwater laser-induced breakdown spectroscopy: Optimisation of the plasma and cavitation bubble for clear observation of atomic spectral lines
No full text- …
