[Show abstract][Hide abstract] ABSTRACT: We have conducted an experimental study exploring the possible application of laser-induced breakdown spectroscopy (LIBS) for practical and highly sensitive detection of metal impurities in water. The spectrochemical measurements were carried out by means of a 355 nm Nd-YAG laser within N<sub>2</sub> and He gas at atmospheric pressures as high as 2 kPa. The aqueous samples were prepared as thin films deposited on indium-tin oxide (ITO) glass by an electrolysis process. The resulting emission spectra suggest that concentrations at parts per billion levels may be achieved for a variety of metal impurities, and it is hence potentially feasible for rapid inspection of water quality in the semiconductor and pharmaceutical industries, as well as for cooling water inspection for possible leakage of radioactivity in nuclear power plants. In view of its relative simplicity, this LIBS equipment offers a practical and less costly alternative to the standard use of inductively coupled plasma-mass spectrometry (ICP-MS) for water samples, and its further potential for in situ and mobile applications.
[Show abstract][Hide abstract] ABSTRACT: An experimental study has been performed on the gas pressure and laser energy dependent variations of plasma emission intensities in Ar, He and N2 ambient gases induced by picosecond (ps) Nd-YAG laser irradiation on low alloy steel (JSS) samples. The study is aimed to demonstrate distinct advantage of using low pressure He ambient gas in combination with ps laser for the sensitive ppm level detection of C, Si and Cr emission lines in the UV-VIS spectral region. The much shorter pulses of ps laser are chosen for the effective ablation at much lower energy and for the benefit of reducing the undesirable long heating of the sample surface. It is found that the C I 247.8 nm, Fe I 253.5 nm, and Si I 251.4 nm emission lines induced by the ps laser at 15 mJ are readily detected with He ambient gas of 2.6 kPA, featuring generally sharp spectral signals with very low background. The following experimental results using samples with various concentrations of C, Si and Cr impurities are shown to produce for each of those elements a linear calibration line with extrapolated zero intercept, demonstrating the applicability for their quantitative analyses, with a preliminary estimated detection limits of 20 μg/g, 15 μg/g, and 5 μg/g, for C, Si, and Cr, respectively. The possibility of applying the same setup for concentration depth profiling is also demonstrated.
Full-text · Article · Sep 2015 · Spectrochimica Acta Part B Atomic Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: An experimental study is conducted on the possibility and viability of performing spectrochemical analysis of carbon and other elements in trace amount in Mars, in particular, the clean detection of C, which is indispensible for tracking the sign of life in Mars. For this study, a nanosecond Nd-YAG laser is employed to generate plasma emission from a pure copper target in CO2 ambient gas of reduced pressure simulating the atmospheric condition of Mars. It is shown that the same shock wave excitation mechanism also works this case while exhibiting remarkably long cooling stage. The highest Cu emission intensities induced by 4 mJ laser ablation energy is attained in 600Pa CO2 ambient gas. Meanwhile the considerably weaker carbon emission from the CO2 gas appears relatively featureless over the entire range of pressure variation, posing a serious problem for sensitive trace analysis of C contained in a solid sample. Our time resolved intensity measurement nevertheless reveals earlier appearance of C emission from the CO2 gas with a limited duration from 50ns to 400ns after the laser irradiation, well before the initial appearance of the long lasting C emission from the solid target at about 1μs, due to the different C-releasing processes from their different host materials. The unwanted C emission from the ambient gas can thus be eliminated from the detected spectrum by a proper time gated detection window. The excellent spectra of carbon, aluminum, calcium, sodium, hydrogen, and oxygen obtained from an agate sample are presented to further demonstrate and verify merit of this special time gated LIBS using CO2 ambient gas and suggesting its viability for broad ranging in-situ applications in Mars.
No preview · Article · Aug 2015 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: We report in this paper the results of an experimental study on the spectral and dynamical
characteristics of plasma emission induced by 1 mJ picoseconds (ps) Nd-YAG laser using spatially
resolved imaging and time resolved measurement of the emission intensities of copper sample.
This study has provided the experimental evidence concerning the dynamical characteristics of the
excitation mechanisms in various stages of the plasma formation, which largely consolidate the
basic scenarios of excitation processes commonly accepted so far. However, it is also clearly shown
that the duration of the shock wave excitation process induced by ps laser pulses is much shorter
than those observed in laser induced breakdown spectroscopy employing nanosecond laser at
higher output energy. This allows the detection of atomic emission due exclusively to He assisted
excitation in low pressure He plasma by proper gating of the detection time. Furthermore, the
triplet excited state associated with He I 587.6 nm is shown to be the one most likely involved
in the process responsible for the excellent spectral quality as evidenced by its application to
spectrochemical analysis of a number of samples. The use of very low energy laser pulses also
leads to minimal destructive effect marked by the resulted craters of merely about 10 micro meter diameter
and only 10 nm deep. It is especially noteworthy that the excellent emission spectrum of deuterium
detected from D-doped titanium sample is free of spectral interference from the undesirable
ubiquitous water molecules without a precleaning procedure as applied previously and yielding
an impressive detection limit of less than 10 micro gram/g. Finally, the result of this study also shows a
promising application to depth profiling of impurity distribution in the sample investigated.
Full-text · Article · Jun 2015 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: We report the results of experimental study on CN 388.3 nm and C I 247.8 nm emission
characteristics using 40 mJ laser irradiation with He and N2 ambient gases. The results obtained
with N2 ambient gas show undesirable interference effect between the native CN emission and the
emission of CN molecules arising from the recombination of native C ablated from the sample
with the N dissociated from the ambient gas. This problem is overcome by the use of He ambient
gas at low pressure of 2 kPa, which also offers the additional advantages of cleaner and stronger
emission lines. The result of applying this favorable experimental condition to emission
spectrochemical measurement of milk sample having various protein concentrations is shown to
yield a close to linear calibration curve with near zero extrapolated intercept. Additionally, a low
detection limit of 5 lg/g is found in this experiment, making it potentially applicable for
quantitative and sensitive CN analysis. The visibility of laser induced breakdown spectroscopy
with low pressure He gas is also demonstrated by the result of its application to spectrochemical
analysis of fossil samples. Furthermore, with the use of CO2 ambient gas at 600 Pa mimicking the
Mars atmosphere, this technique also shows promising applications to exploration in Mars.
Full-text · Article · Mar 2015 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: A systematic study has been performed on the spectral characteristics of the full spectrum of He emission lines and their time-dependent behaviors measured from the He gas plasmas generated by a nanosecond neodymium-doped yttrium aluminum garnet laser. It is shown that among the major emission lines observed, the triplet He(I) 587.6 nm emission line stands out as the most prominent and long-lasting line, associated with de-excitation of the metastable triplet (S = 1) excited state (1s1 3d1). The role of this metastable excited state is manifested in the intensity enhancement and prolonged life time of the Cu emission with narrow full width half-maximum, as demonstrated in an orthogonal double-pulse experiment using a picosecond laser for the target ablation and a nanosecond laser for the prior generation of the ambient He gas plasma. These desirable emission features are in dire contrast to the characteristics of emission spectra observed with N2 ambient gas having no metastable excited state, which exhibit an initial Stark broadening effect and rapid intensity diminution typical to thermal shock wave-induced emission. The aforementioned He metastable excited state is therefore responsible for the demonstrated favorable features. The advantage of using He ambient gas in the double-pulse setup is further confirmed by the emission spectra measured from a variety of samples. The results of this study have thus shown the potential of extending the existing laser-induced breakdown spectroscopy application to high-sensitivity and high-resolution spectrochemical analysis of wide-ranging samples with minimal destructive effect on the sample surface.
[Show abstract][Hide abstract] ABSTRACT: A systematic study has been performed on the spectral characteristics of the full spectrum of He emission lines and their time-dependent behaviors measured from the He gas plasmas generated by a nanosecond neodymium-doped yttrium aluminum garnet laser. It is shown that among the major
emission lines observed, the triplet He(I) 587.6 nm emission line stands out as the most prominent and long-lasting line, associated with de-excitation of the metastable triplet (S = 1) excited state (1s1 3d1). The role of this metastable excited state is manifested in
the intensity enhancement and prolonged life time of the Cu emission with narrow full width half-maximum, as demonstrated in an orthogonal double-pulse experiment using a picosecond laser for the target ablation and a nanosecond laser for the prior generation of the ambient He gas plasma.
These desirable emission features are in dire contrast to the characteristics of emission spectra observed with N2 ambient gas having no metastable excited state, which exhibit an initial Stark broadening effect and rapid intensity diminution typical to thermal shock wave-induced
emission. The aforementioned He metastable excited state is therefore responsible for the demonstrated favorable features. The advantage of using He ambient gas in the double-pulse setup is further confirmed by the emission spectra measured from a variety of samples. The results of this study
have thus shown the potential of extending the existing laser-induced breakdown spectroscopy application to high-sensitivity and high-resolution spectrochemical analysis of wide-ranging samples with minimal destructive effect on the sample surface.
Full-text · Article · Dec 2014 · Applied Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: An experimental study has been performed on the pressure-dependent plasma emission intensities in Ar, He, and N2 surrounding gases with the plasma induced by either nanosecond (ns) or picosecond (ps) yttrium aluminum garnet laser. The study focused on emission lines of light elements such as H, C, O, and a moderately heavy element of Ca from an agate target. The result shows widely different pressure effects among the different emission lines, which further vary with the surrounding gases used and also with the different ablation laser employed. It was found that most of the maximum emission intensities can be achieved in Ar gas plasma generated by ps laser at low gas pressure of around 5 Torr. This experimental condition is particularly useful for spectrochemical analysis of light elements such as H, C, and O, which are known to suffer from intensity diminution at higher gas pressures. Further measurements of the spatial distribution and time profiles of the emission intensities of H I 656.2 nm and Ca II 396.8 nm reveal the similar role of shock wave excitation for the emission in both ns and ps laser-induced plasmas, while an additional early spike is observed in the plasma generated by the ps laser. The suggested preference of Ar surrounding gas and ps laser was further demonstrated by outperforming the ns laser in their applications to depth profiling of the H emission intensity and offering the prospect for the development of three-dimensional analysis of a light element such as H and C.
Full-text · Article · Nov 2013 · Applied Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: A time-resolved orthogonal double pulse laser-induced breakdown spectroscopy (LIBS) with helium surrounding gas is developed for the explicit demonstration of time mismatch between the passage of fast moving impurity hydrogen atoms and the formation of thermal shock wave plasma generated by the relatively slow moving major host atoms of much greater masses ablated from the same sample. Although this so-called 'mismatching effect' has been consistently shown to be responsible for the gas pressure induced intensity diminution of hydrogen emission in a number of LIBS measurements using different ambient gases, its explicit demonstration has yet to be reported. The previously reported helium assisted excitation process has made possible the use of surrounding helium gas in our experimental set-up for showing that the ablated hydrogen atoms indeed move faster than the simultaneously ablated much heavier major host atoms as signaled by the earlier H emission in the helium plasma generated by a separate laser prior to the laser ablation. This conclusion is further substantiated by the observed dominant distribution of H atoms in the forward cone-shaped target plasma.
Full-text · Article · Feb 2013 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 μs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 μg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 μm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.
Full-text · Article · Mar 2012 · Analytical Chemistry
[Show abstract][Hide abstract] ABSTRACT: An experimental study of double pulse LIBS is performed for the development of highly sensitive and quantitative analysis of Cl and Ca for the strength evaluation of concrete. The two lasers employed are arranged in orthogonal geometry and operated for delayed ablation with delay time of 10 μs, using He ambient gas at atmospheric pressure. The very large intensity enhancement is obtained over those detected with single pulse operation without generating the He plasma. It is most remarkable that the same sharpness and intensity enhancement observed in the previous double pulse experiment with 37 mJ laser ablation energy is achieved in the present experiment with much lower ablation energy of merely 2.5 mJ, resulting in average crater size of about 10 μm in diameter. Further, a linear relation is obtained between the Cl concentration and its emission intensity in alumina samples, while an estimated limit of detection of 80 ppm is obtained by using concrete sample, which is adequate for highly sensitive quantitative Cl analysis in concrete.
Full-text · Article · Mar 2012 · Spectrochimica Acta Part B Atomic Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: An experimental study on picosecond laser induced plasma spectroscopy of a zircaloy sample with low-pressure surrounding helium gas has been carried out to demonstrate its potential applicability to three-dimensional quantitative micro-analysis of deuterium impurities in zircaloy. This was achieved by adopting the optimal experimental condition ascertained in this study, which is specified as 7 mJ laser energy, 1.3 kPa helium pressure, and 50 μs measurement window, and which was found to result in consistent D emission enhancement. Employing these operational parameters, a linear calibration line exhibiting a zero intercept was obtained from zircaloy-4 samples doped with various concentrations of D impurity, regarded as surrogates for H impurity. An additional measurement also yielded a detection limit of about 10 μg/g for D impurity, well below the acceptable threshold of damaging H concentration in zircaloy. Each of these measurements was found to produce a crater size of only 25 μm in diameter, promising its application for performing less-destructive measurements. The result of this study has thus paved the way for conducting a further experiment with hydrogen-doped zircaloy samples and the further technical development of a three-dimensional quantitative micro-analysis of detrimental hydrogen impurity in zircaloy vessels used in nuclear power plants.
[Show abstract][Hide abstract] ABSTRACT: An experiment was performed for the observation of H emission induced in a cooled laser-induced atmospheric pressure gas plasma of He atoms in their metastable excited state. The strong H emission detected clearly established, to the exclusion of other well known major excitation processes, the exclusive contribution of the He-induced excitation (HIE) mechanism. The process is suggested to take place by means of energy transfer from the excited He atoms to the H atoms via Penning collision induced ionization involving electron exchange. The result further shows that this mechanism may also work for elements other than H and thereby strongly suggests the use of ambient He gas to broaden and complement the applications of standard laser-induced breakdown spectroscopy.
Full-text · Article · May 2011 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: The direct analysis of powder samples has been carried out successfully by utilizing lasercontrolleddust production in a small chamber pressurized to one atmosphere with He. A 355-nm Nd:YAG laser (5 mJ, 10 Hz) was focused on the surface of the powder sample to form a microplasma, which released a tiny amount of powder in the form of a dust. A 1064-nm Nd:YAG laser operating at higher energy (110 mJ, 10 Hz), which is not synchronized with the 355-nm Nd:YAG laser, was then used to form a He gas breakdown plasma in the dust region to atomize and excite the dust. We assumed that this excitation process involved metastable He atoms produced in the breakdown plasma. The emission spectra obtained for a variety of powder samples by using this method were found to be of good quality. Furthermore, the method can be used to analyze liquid samples by placing a drop of liquid onto a small piece of cotton to avoid splashing. Indeed, the rapid and semi-quantitative analysis of both powder and liquid samples has proved to be possible using the present technique. One advantage of this technique is that analyses can be conducted even when the samples are available in only very small amounts.
No preview · Article · May 2011 · Journal- Korean Physical Society
[Show abstract][Hide abstract] ABSTRACT: An experimental study of ultraviolet (UV) laser-induced plasma spectroscopy (LIPS) on Ti samples with low-pressure surrounding He gas has been carried out to demonstrate its applicability to quantitative micro-analysis of deuterium impurities in titanium without the spectral interference from the ubiquitous surface water. This was achieved by adopting the optimal experimental condition ascertained in this study, which is specified by 5 mJ laser energy, 10 Torr helium pressure, and 1-50 mus measurement window, which resulted in consistent D emission enhancement and effective elimination of spectral interference from surface water. As a result, a linear calibration line exhibiting a zero intercept was obtained from Ti samples doped with various D impurity concentrations. An additional measurement also yielded a detection limit of about 40 ppm for D impurity, well below the acceptable threshold of damaging H concentration in Ti and its alloys. Each of these measurements was found to produce a crater size of only 25 mum in diameter, and they may therefore qualify as nondestructive measurements. The result of this study has therefore paved the way for conducting further experiments with hydrogen-doped Ti samples and the technical implementation of quantitative micro-analysis of detrimental hydrogen impurity in Ti metal and its alloys, which is the ultimate goal of this study.
[Show abstract][Hide abstract] ABSTRACT: An experimental study has been performed on the effects of crater depth on the hydrogen and deuterium emission intensities measured from laser plasmas generated in low-pressure helium ambient gas from zircaloy-4 samples doped with different H and D impurity concentrations as well as a standard brass sample for comparison. The results show that aside from emission of the host atom, the emission intensities of other ablated atoms of significantly smaller masses as well as that of the He atom generally exhibit relatively rapid initial decline with increasing crater depth. This trend was found to have its origin in the decreasing laser power density arriving at the crater bottom and thereby weakened the shock wave generated in the crater. As the crater deepened, the declining trend of the intensity appeared to level off as a result of compensation of the decreasing laser power density by the enhanced plasma confinement at increasing crater depth. Meanwhile, the result also reveals the significant contribution of the He-assisted excitation process to the doped hydrogen and deuterium emission intensities, leading to similar crater-depth dependent variation patterns in contrast to that associated with the surface water, with growing dominance of this common feature at the later stage of the plasma expansion. Therefore, a carefully chosen set of gate delay and gate width which are properly adapted to the crater-depth dependent behavior of the emission intensity may produce the desired intrinsic emission data for quantitative depth profiling of H impurity trapped inside the zircaloy wall.
No preview · Article · Oct 2009 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: An experimental study was conducted on the spatial distributions of hydrogen emission intensities from low-pressure plasmas generated by laser ablation of zircaloy-4 and black stone targets in nitrogen and helium ambient gases. In addition to confirming the previously observed intensity enhancement effect in ambient helium gas, the hydrogen and helium emission intensities measured along the plasma expansion direction revealed remarkable extended spatial distributions featuring unexpected maxima near the far end of the plasma where the available shock-wave generated thermal excitation energy should have been significantly reduced. This “anomalous” feature necessarily implied the presence of an additional excitation process beside the well known shock-wave excitation process which is responsible for the plasma emission of heavy atoms in low-pressure ambient gas. Further analysis of the data led to a suggested physical mechanism explaining the possible contribution of a helium metastable excited state to the unusual phenomenon observed in this experiment.
No preview · Article · Sep 2009 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: A series of measurements have been performed on the time dependences of the intensities of helium, hydrogen, and deuterium emission lines from the corresponding laser-induced helium plasma at atmospheric pressure for two different He flow rates. The prolonged H <sub>α</sub> and H <sub>β</sub> emissions along with their constant intensity ratio over a relatively extended period indicate the need to provide an alternative excitation mechanism other than the well-known thermal excitation process in a hot plasma. This additional excitation mechanism is also related to the metastable excited state of a He atom as indicated by the similar characteristics of the observed time dependence of the emission intensities. The enhanced intensity and lifetime of He emission at a high He flow rate was explained in terms of the collision-induced increase in the number of He atoms excited to above the 2 <sup>1</sup>S<sub>0</sub> metastable state, which was also responsible for the delayed excitation of H and D atoms via an energy transfer mechanism involving a Penning-like chemi-ionization process. Finally, the benefits of He-assisted delayed excitation of H and D atoms and the aforementioned enhanced intensity and lifetime at a high He flow rate were demonstrated by the achievement of clearly resolved H <sub>α</sub> and D <sub>α</sub> emission lines.
No preview · Article · Jun 2009 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: An experimental study was performed on the N <sub>2</sub> -induced quenching of He-induced intensity enhancement effect in reduced-pressure plasma emission produced by Nd-YAG irradiation on solid zircaloy and porous fossil samples. The spatial distributions and temporal variations in the emission intensities show pronounced intensity quenching effects on the He I 667.9 nm, H I 656.2 nm, and D I 656.1 nm emission lines in both samples when a tiny amount (5% by volume) of nitrogen was added to helium gas, while leaving the spatial and temporal intensity profiles of the heavier Zr and Ca atoms virtually unaffected. In both cases of different ambient gases, the spatial and temporal variations in the He, H, and D emission intensities exhibit distinct features and changes, which are clearly distinguishable from those observed on the Zr and Ca emission lines, which were mainly produced by the shock-wave induced thermal excitation process. The analysis of these data unambiguously revealed the presence of an additional and distinct “He-assisted” excitation mechanism in the He plasma, which was further suggested to be related to the He metastable excited state. The quenching effect was therefore explained as a consequence of energy depletion of the He metastable excited state triggered by the Penning ionization process induced by the presence of nitrogen. This also explains the relatively insensitive response of the Zr and Ca emission intensity profiles to nitrogen addition despite the increased plasma electron density resulting from the ionization process.
No preview · Article · Feb 2009 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: 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 microm 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.
No preview · Article · May 2008 · Analytical and Bioanalytical Chemistry