An improved approach for hydrogen analysis in metal samples using single laser-induced gas plasma and target plasma at helium atmospheric pressure

We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration of the conventional LIBS method. PACS 51-52     

Spectrochemical analysis of powder using 355 nm Nd-YAG laser-induced low-pressure plasma

The applicability of spectrochemical analysis of minute amounts of powder samples was investigated using an ultraviolet Nd-YAG laser (355 nm) and low-pressure ambient air. A large variety of chemical powder samples of different composition were employed in the experiment. These included a mixture of copper(II) sulfate pentahydrate, zinc sulfide, and chromium(III) sulfate n-hydrate powders, baby powder, cosmetic powders, gold films, zinc supplement tablet, and muds and soils from different areas. The powder samples were prepared by pulverizing the original samples to an average size of around 30 μm in order to trap them in the tiny micro holes created on the surface of the quartz subtarget. It was demonstrated that in all cases studied, good quality spectra were obtained with low background, free from undesirable contamination by the subtarget elements and featuring ppm sensitivity. A further measurement revealed a linear calibration curve with zero intercept. These results clearly show the potential application of this technique for practical qualitative and quantitative spectrochemical analysis of powder samples in various fields of study and investigation.     

Film analysis employing subtarget effect using 355 nm Nd-YAG laser-induced plasma at low pressure

The applicability of spectrochemical analysis for liquid and powder samples of minute amount in the form of thin film was investigated using ultraviolet Nd-YAG laser (355 nm) and low-pressure ambient air. A variety of organic samples such as commercial black ink usually used for stamp pad, ginseng extract, human blood, liquid milk and ginseng powder was prepared as film deposited on the surface of an appropriate hard substrate such as copper plate or glass slide. It was demonstrated that in all cases studied, good quality spectra were obtained with very low background and free from undesirable contamination by the substrate elements, featuring ppm or even sub-ppm sensitivity and worthy of application for quantitative analysis of organic samples. The proper preparation of the films was found to be crucial in achieving the high quality spectra. It was further shown that much inferior results were obtained when the atmospheric-pressure (101 kPa) operating condition of laser-induced breakdown spectroscopy or the fundamental wavelength of the Nd-YAG laser was employed due to the excessive or improper laser ablation process.     

Optical interferometry applied to analyze deformation and fracture of aluminum alloys

Deformation and fracture of aluminum alloys are studied using a unique optical technique. This technique is based on a new optical pattern that we recently discovered in a fringe system generated by speckle pattern interferometry. The investigation has revealed that the optical pattern represents a band structured deformation called the mesoband which is substantially related to stress concentration. Described in detail are the Characteristics of this optical pattern; they are explained in connection with the development of plastic deformation and fracture behavior. Several features of this optical pattern are presented that manifest some important mechanical states of the material in the prefracture stage and they can be used to predict the location and timing of a fracture.     

Comparative study of laser-induced plasma emission of hydrogen from zircaloy-2 samples in atmospheric and low pressure ambient helium gas

An experimental study has been performed to demonstrate the advantage of employing ambient helium gas in the spectral quality improvement of hydrogen emission in laser-induced plasma from zircaloy-2 samples at both atmospheric and low gas pressure. It was further shown that the optimal results achieved in the two pressure regimes require the adoption of different sets of experimental parameters consisting of the laser energy, the focusing lens position and the detection gate delay. A strictly linear calibration line with extrapolated zero intercept was nevertheless exhibited in the case of atmospheric gas pressure only. Additional time-evolution measurement of the emission intensities of hydrogen, helium and zirconium clearly suggests a distinctly different excitation mechanism for hydrogen atoms associated with the presence of ambient helium atoms and their meta-stable excited state. PACS 52.38 Mf     

Some notes on the role of meta-stable excited state of helium atom in laser-induced helium gas breakdown spectroscopy

A study of the experimental results on the plasma emissions of water and ethanol vapor samples, induced by Nd:YAG laser in ambient helium and nitrogen gases at atmospheric pressure, is presented here. The result reveals distinct geometrical and spectral characteristics of the plasma emissions generated in the helium gas when compared to those observed from nitrogen gas plasma. Most remarkable is the narrow line width and low continuum background exhibited by emission lines of the analyte atoms from helium plasma, including the hydrogen emission line which is known to suffer from notorious broadening effects in conventional laser induced breakdown spectroscopy (LIBS). It is further shown on the basis of the measured spatial distributions and time profiles of the emission intensities, that the excellent spectral quality is attained by taking advantage of the meta-stable excited state of helium atoms for the delayed excitation of the hydrogen and other analyte atoms, this allows the detection of those atomic emissions to be performed under more favorable conditions. The result of this study has thus demonstrated the feasibility of achieving high-quality spectrochemical analysis, including hydrogen analysis with laser-induced helium gas breakdown spectroscopy. PACS 52.38.Mf     

Effects of mass difference on pressure-dependent emission characteristics in laser-induced plasma spectroscopy

A comprehensive experimental study was performed to demonstrate the effects of ambient air pressure on the emission characteristics of analyte elements in a variety of host materials in laser-induced plasma spectroscopy in low ambient air pressures. It was shown that the pressure-dependent characteristics of the emission lines are generally influenced by host elements when significant mass difference exists between the analyte and the host elements. Further investigation on the time profiles of the spatially integrated emission intensities reveal the important interplay among the dynamical factors associated with the mass-difference effect, which effectively influence the shock wave excitation process and hence the related emission intensities. The result of this study also indicates the need of proper control of time delay for the detection of maximum emission intensity in the cases considered. PACS 50.52