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High-sensitivity detection of hydrogen (H) contained in zircaloy-4, a commonly used material for nuclear fuel containers, is crucial in a nuclear power plant. Currently, H detection is performed via gas chromatography, which is an offline and destructive method. In this study, we developed a technique based on metastable excited-state He-assisted excitation to achieve excellent quality of H emission spectra in double-pulse orthogonal laser-induced breakdown spectroscopy (LIBS). The production of metastable excited-state He atoms is optimized by using LiF as sub-target material. The results show a narrow full-width-at-half-maximum of 0.5 Å for the H I 656.2 nm emission line, with a detection limit as low as 0.51 mg/kg. Thus, using this novel online method, H in zircaloy-4 can be detected efficiently, even at very low concentrations.

Laser-induced breakdown spectroscopy (LIBS) to detect the light elements such as lithium (Li) and boron (B) and heavy elements such as copper (Cu) and lead (Pb) in raw fish samples is reported in this work. This is made possible by understanding that the soft target absorbs recoil energy and as a result, the ablated atoms gushing from the soft target do not acquire sufficient speed to form a shock wave. In order to overcome this problem, we set a subtarget on the back of the soft target so as to produce the repulsion force by which the gushing speed of the ablated atoms is increased, yielding a sufficiently high plasma temperature or sufficiently large thermal energy needed for the excitation of the ablated atoms. Excellent spectral qualities of various soft samples such as margarine, butter, peanut butter, strawberry jam, raw tuna, raw gindara, and raw salmon are presented. Furthermore, a linear calibration curve with a zero intercept is also obtained for Li, Cu, and Pb. The detection limit of Li, Cu, and Pb is found to be around 0.1 mg/L. This modification of LIBS for soft samples by using a subtarget effect clearly promises a rapid and in situ soft sample analysis since there is practically no sample digestion in the analysis.

Background: Hydrogen (H) and Carbon (C) are major elements that occur in various materials, including organic matter. The identification and analysis of C and H are necessary for several fields. LIBS is an excellent method for such analysis because it is rapid, and can be conducted remotely. The technique has been employed for the analysis of H in zircaloy metals. However, few studies on the emission characteristics of H and C in various gases have been undertaken because of the difficulty of identifying H and C using standard LIBS techniques. In this work, the emission characteristics of H and C were studied using pulsed CO2 LIBS. H and C elements were obtained from ethanol vapor. Various gas environments were employed, including Nitrogen (N2), Argon (Ar), and Helium (He) gases, in order to study the stability of the laser-induced plasma, the plasma lifetime, and the excitation mechanisms of H and C. Methods: The LIBS system used in this work consisted of a pulsed TEA CO2 laser (Shibuya SQ 2000), pulse generator, and optical multichannel analyzer. In this work, the laser with a wavelength of 10.6 µm, pulse duration of 200 ns, and pulse energy of 3 J, was used as the irradiation source. The laser energy used was 1.5 J. The laser was irradiated, and focused, using a 200 mm zinc selenide (ZnSe) lens, onto a metal surface in order to initiate and induce a luminous plasma. The sample used in this study was ethanol vapor, obtained from ethanol (99.5%, Merck). For this purpose, 10 mL ethanol was poured into a glass beaker, and this was placed into a closed chamber that could be evacuated by ambient gases including N2, Ar, and He gases. Results: Identification of H emission line has been successfully carried out using this present technique demonstrated in various gases including N2, Ar, and He. From the results, it was observed that in N2 gas, the Hα I 656.3 nm emission line was clearly expressed, with a wide, full-width halfmaximum, and quite a low emission intensity. Conclusion: The emission characteristics of H and C in laser-induced plasma, produced in various ambient gases, including N2, Ar, and He, were studied. The emission spectra of Hα and Hβ were expressed clearly, with high intensity and low background emission, in He, while they were broad and had high background emissions in N2 and Ar. Based on the time-resolved emissions, the Hα emission had a longer lifetime in Ar and He. It was assumed that the metastable atoms of Arand He were predominant in the excitation process of H and C. The characteristics of the H and C emissions in various gases are important in selecting a suitable ambient gas for the study of light atomic emission in the medical field, which mostly deals with organic materials containing H, C, and oxygen.

A self-reversal effect in plasma has affected the accuracy of laser-induced breakdown spectroscopy (LIBS). This effect becomes pronounced in a high-density and inhomogeneous plasma, which is commonly generated in UV LIBS due to efficient ablation of the sample by UV irradiation. Here we present a simple method to suppress the self-reversal effect in UV LIBS at atmospheric pressure utilizing an air spark-assisted excitation. We simultaneously generated the air spark and target plasma by adjusting the lens’ focal point position relative to the sample surface. The interaction between the air spark’s tail and target plasma helps reduce the number of cold ground-state atoms at the periphery of the target plasma. Under this condition, we significantly suppressed the self-reversal effect in the resonance lines of high-concentration aluminum. The time-resolved features show that the emission lines of Al I 394.40 nm and Al I 396.15 nm obtained using the proposed approach are free from self-reversal. These results indicate that the proposed technique can improve the plasma’s homogeneity and, therefore, the spectral quality of resonance lines of nanosecond UV LIBS.

This study introduces a novel and simple way to suppress the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) by utilizing a defocusing laser irradiation technique. For this purpose, a Nd:YAG laser with a wavelength of 1,064 nm and repetition rate of 10 Hz with energy in the range of 10 mJ-50 mJ was used. The laser irradiation was focused by using a 150-mm-focal-length plano-convex lens onto the sample surface under defocusing of approximately -6 mm. Potassium chloride (KCl) and sodium chloride (NaCl) pellet samples were used to demonstrate this achievement. When the defocus position is adjusted to -6 mm for KCl and NaCl samples, the self-reversal in the emission lines of K I 766.4 nm, K I 769.9 nm, Na I 588.9 nm, and Na I 589.5 nm vanish. Meanwhile, the FWHM values of K I 766.4 and K I 769.9 nm are 0.29 nm and 0.23 nm, respectively, during -6 mm defocus laser irradiation, as opposed to 1.24 nm and 0.86 nm under tight focus laser irradiation. Additionally, this work demonstrates that, when the laser energy is changed between 10 and 50 mJ, no self-reversal occurs in the emission lines when -6 mm defocus laser irradiation is applied. Finally, a linear calibration curve was generated using KCl at a high concentration ranging between K concentrations from 16.6% to 29%. It should be noted that, even at such high K concentrations, the calibration curve is still linear. This means that self-absorption is almost negligible. This simple change in defocus laser irradiation will undoubtedly contribute to the suppression of the self-absorption phenomenon, which disrupts LIBS analytical results.

We report the results of an experimental study of food analysis using Nd:YAG nanosecond (ns) laser at various pulse energies in atmospheric ambient air and He ambient gas at different pressures. In contrary to previous results indicating the unfavorable applications of LIBS to food analysis using lower pulse energies and atmospheric ambient air, this study demonstrates clearly the excellent spectral quality obtained from a number of food samples of different hardnesses with high energy (132 mJ) ns laser pulses and 20 Torr He ambient gas. A series of energy dependent intensity measurements show that the intensities generally increase with higher laser energies and harder samples which can be attributed to the generation of stronger shock wave plasma and the subsequently induced He assisted excitation (HAE) mechanism which is responsible for the sharp emission lines and the very low spectral background. Using mochi samples with different Cu impurity contents, this experiment further reveals the existence of a linear calibration line and a detection limit of sub ppm level. The results of this study have thus suggested the promising development of low cost and practical technique for quantitative food analysis in place of more expensive and bulkies picosecond laser used before.

This study is aimed at elucidating the physical processes responsible for the excellent spectral qualities in terms of full width at half-maximum (fwhm) and signal-to-noise (S/N) ratio shown in a special double pulse laser-induced spectroscopy. Apart from the use of atmospheric He ambient gas, the achievement is due to the first laser for generating He gas plasma and the subsequent use of the second laser pulse for target ablation, in opposite order of the two-laser operations in conventional double pulse LIBS. This setup allows adjustments of the many experimental parameters to yield the optimal condition resulting in 0.03 nm fwhm and around 1000× S/N ratio of Cu I 521.8 nm and far surpasses the spectral qualities obtained by other techniques. This is obtained by allowing the crucial separation of the target plasma from the He gas plasma and thereby enabling the He-assisted excitation (HAE) to play its full and unique role of nonthermal excitation, taking advantage of metastable excited He atoms in the He plasma and the Penning-like energy transfer process. This excellent performance is further verified by its successful application analysis of Cr in low alloy steel samples, with the presence of smooth linear calibration lines, signifying the absence of the self-absorption effect well-known in ordinary LIBS.

Analysis of impurity in powder samples has been made by using metal-assisted laser-induced plasma spectroscopy utilizing a pulsed CO2 laser. Various powders including food powder, supplement powder, baby powder, and medicine powder were employed as sample materials. Experimentally, the powder sample was tightly put in a hole made on a metal plate and a metal mesh was placed on the powder surface. A pulse CO2 laser (10.6 μm, 1500 mJ) was irradiated on the powder surface passing through the metal mesh. Luminous plasma was induced by mesh just above the mesh when a part of laser energy attacked the mesh. The other part of laser energy impinged the powders and ablated fine particles of powder to the plasma to be atomized and excited. Identification and analysis of elements in powder were successfully conducted. A linear calibration curve of Cu in baby powder has been demonstrated with an intercept zero, certifying that the present technique was a high possibility to be employed for semi-quantitative analysis of elements in powder material. It was proved that by applying the present technique and employing a condensation technique, the detection sensitivity of Cr impurity in the powder sample increased about twenty times compared to the case without condensation. The limit of detection of Cr in rice powder sample was 25 mg/kg. The proposed method was very convenient for the identification and analysis of elements in the powder sample.

Analysis of carbon (C) in soil has been successfully made by laser plasma spectroscopy using a pulsed carbon dioxide (CO2) laser. Fine particles of soil sample were attached on a surface of the metal subtarget by adding a small amount of moisture; the metal was used to initiate the gas plasma. Experimentally, a pulsed laser was focused on the subtarget to induce a luminous plasma. The particles were vaporized and entered the plasma region. Dissociation and excitation happened in the high-temperature plasma region. The result certified that an analysis of C in soil can be demonstrated. A further measurement revealed that a calibration curve of C was successfully carried out. The limit of detection of C in the soil was around 23 mg/kg.

Self-absorption, which is known to severely disturb identification of the emission peak intensity in emission-based spectroscopy, was first studied using ordinary single pulse laser-induced breakdown spectroscopy (LIBS). It was found that severe self-absorption, with an evident self-reversal, occurs in the resonance emission lines of high concentration Na, K, and Al, and thus it is impossible to obtain the linear calibration curve required for quantitative analysis. To overcome this problem, we introduce a double pulse orthogonal technique in which the first laser is fired in a parallel orientation at a varied distance of 2–6 mm from the sample surface. It is well known that the strong shock wave generated by this laser irradiation temporarily creates a vacuum-like condition immediately in front of the sample surface. This action is followed by a second laser irradiation oriented perpendicular to the sample surface. The sample ablated by the second laser irradiation expands following the shockwave excitation process in the vacuum-like air atmosphere created by the first laser. The obtained spectra of the resonance emission lines of high concentration Na, K, and Al are free from the self-reversal and weakly affected by the self-absorption effect. A linear calibration curve that intercepts near zero point for K element over a wide concentration range is also demonstrated in this study. This simple modification is considered notably helpful in overcoming the self-absorption that occurs in ordinary single pulse atmospheric pressure LIBS.

Carbon detection is usually difficult to carry out with high sensitivity and minimally destructive effect. While the conventional laser induced breakdown spectroscopy (LIBS) method operated with atmospheric ambient air is well known as a powerful and versatile analytical tool, it suffers nevertheless from the low sensitivity of C detection when measured in both atmospheric and low pressure ambient air with the more adverse effect found in the former case. This was shown to have its origin in the serious time mismatching effect between the formation of the shock wave plasma by the ablated major host elements and the premature fast passage of the much lighter ablated C atom. However, this study shows the result of high sensitivity C analysis of stone samples using LIBS technique with relatively low laser pulse energy of 60 mJ and low pressure He ambient gas without showing visible surface damage. The helium gas provides the additional delayed excitation by the He metastable excited states through the Penning-like ionization process. The C emission intensities measured from the jasper and black stone in 2.6 kPa He ambient gas are in general significantly higher than those measured in 0.5 kPa ambient air. The enhancement is shown to increase reaching an 8 fold enhancement with increased laser energy up to 60 mJ before undesirable surface damage is created. A further measurement of C emission using pelletized KBr mixtures with various CaCO3 concentrations reveals a straight calibration line of rather large slope with extrapolated zero intercept and estimated detection limit of around 0.6 ppm, demonstrating its potential application for highly sensitive quantitative analysis of C with minimal destructive effect.

We present in this report the results of experimental study on the spectrochemical analysis of powder samples using subtarget supported micro mesh (SSMM) sample holder in low pressure ambient gases. The study is substantiated by establishing the analyte excitation mechanism with the evidence of shock wave plasma generation and the high temperature induced subsequently required for the thermal excitation and emission of the ablated atoms. The application of SSMM sample holder using Cu subtarget and stainless steel micro mesh to a number of powder samples in low pressure ambient gases are shown to produce generally sharp emission lines with low background, without suffering from intensity reduction and matrix effect commonly found in the use of pelletized powder samples. The same excellent spectral quality is demonstrated by its application to the analysis of rice samples which is the major staple diets in a large number of countries. In particular the analysis of Zn in rice is shown to exhibit a linear calibration line with extrapolated zero intercept and a detection limit of

Laser-induced gas plasma spectroscopy based on pulsed CO2 laser beam splitting has been applied to the problem of trace film analysis on the silicon surface. In this study, 2.1 J of laser e...

A study is performed to demonstrate the feasibility of applying a microjoule picosecond laser for sensitive and high resolution in-situ Cr analysis with minimal destructive effect. It is aimed for application to quality assessment of steel products and proses control in the related industry as well as field inspection and monitoring of products in used. The feasibility and realization of these applications is examined and verified by the successful generation of shock wave plasma responsible for the shock wave induced thermal excitation of the ablated atoms by means of a ps Nd:YAG laser operated in the energy range of 100 μJ–500 μJ and directly focused onto the solid sample in open ambient air without the use of microscope and sample chamber as commonly employed in all existing μLIBS techniques. The time-dependent intensity variation of the generated micro plasma emission is shown to exhibit all the well-known characteristic structural and dynamical features of shock wave plasma emission. This is followed by further experiment for the ascertainment of the most favorable laser energy of 500 μJ and gate delay of 100 ns for its applications to Cr analysis of standard steel, standard Al samples and precious green stone sample. The resulted spectra all feature very sharp emission lines with low background and yielding an estimated detection limit of lower than 1 ppm and an average crater size of around 7 μm. It is therefore, promising for minimally destructive and highly sensitive in-situ Cr analysis.

A practical alternative of sample preparation technique is proposed for direct powder analysis using laser-induced breakdown spectroscopy (LIBS) instead of the commonly adopted treatment of pelletizing the powder. The resulted pellet is known to suffer from reduced sensitivity of emission. Besides, it may also give rise to interfering effect from the binder emission. We introduce in this report a more practical technique of using a subtarget supported micro mesh (SSMM) powder sample holder. The LIBS spectrum of standard soil powder measured with 13 mJ 1064 nm Nd:YAG laser in 0.65 kPa ambient air is shown to exhibit the sharp emission lines of all the major elements in the sample. A comparison with the emission spectra measured from the pelletized powder, the spectrum obtained using the SSMM sample holder shows distinctly superior spectral quality marked by the absence of matrix effect found in pelletized powder samples, and the much stronger intensity due to the more effective shock wave plasma induced thermal excitation process produced by the hard subtarget in the sample holder. Repeating the measurement on a number of the standard soil samples of various Pb contents is shown to yield a linear calibration line with practically zero intercept and a detection limit of less than 10 ppm. We have thus demonstrated the viability of the proposed powder sample holder for the development of practical and quantitative powder analysis in the field.

An experimental study has been conducted for the practical and in situ application of laser-induced breakdown spectroscopy (LIBS) for the detection of Cs pollutant in water and soil in the nearby area of Fukushima Nuclear Power Station. The spectrochemical measurements were carried out by means of 355 nm Nd-YAG laser with N 2 and He ambient gases at atmospheric and low pressures. The soil samples were prepared by pelletizing the mixtures of 80% soil and 20% KBr while the aqueous samples were prepared as thin films electro deposited on indium tin oxide (ITO) glass. The resulted emission spectra using 0.5 kPa N 2 ambient gas shows the minimum detectable Cs concentration of 0.2 ppm and 0.3 ppm in the water and soil samples, respectively. The result of this experiment has thus demonstrated the viability of the LIBS equipment employed here as a more practical, in-situ and even mobile alternative to the standard use of gamma-ray spectroscopy using germanium detector.

A novel method of laser-induced plasma spectroscopy utilizing a pulsed transversely excited atmospheric CO2 laser has been developed for the high-sensitivity determination of heavy metals in soil. A coarse metal powder was used to trap the soil and to assist with plasma generation. When the CO2 laser (10.6 µm, 1.5 J, 200 ns) was irradiated on the metal and soil powder, a high-temperature and long-lifetime luminous plasma was induced. Fine particles of soil were dissociated and were excited in the plasma region. The method was used for the rapid determination of Cr, Pb, and Hg in loam. The limits of detection for Cr, Pb, and Hg were approximately 0.8, 15, and 0.7 mg/kg, respectively.

An experimental study is conducted in search of the much needed experimental method for practical and minimally destructive analysis of hydrogen (H) and deuterium (D) in a nuclear power plant. For this purpose, a picosecond (ps) Nd:YAG laser is employed and operated with 300-500 μJ output energies in a variety of ambient gases at various gas pressures. The sample chamber used is specially designed small quartz tube with an open end that can be tightly fitted to the sample surface. It is found that ambient Ar gas at reduced pressure of around 0.13 kPa gives the best spectral quality featuring fully resolved H and D emission lines with clearly detectable intensities and practically free from surface water interference. The D emission intensities measured from zircaloy plates containing various concentrations of D impurity are shown to yield a linear calibration line with extrapolated zero intercept, offering its potential application to quantitative analysis. The estimated detection limit of less than 10 ppm is well below the sensitivity limit of around 600 ppm required for the regular inspection of zircaloy tubes in a heavy water nuclear power plant. The use of the exceedingly low laser energy is shown to offer an additional advantage of minimum destructive effect marked by the resulted tiny craters of about 5 μm diameter with 25 μm depth. These results promise the potential development of the desired alternative analytical tool for regular in situ and real time inspection of the zircaloy tubes in a heavy water power plant.

This study demonstrates a new approach for suppressing the self-absorption effect in single-pulse laser-induced breakdown spectroscopy (LIBS) using unusual parallel laser irradiation. A nanosecond Nd:YAG laser with a wavelength of 1064 nm was fired parallel to and focused at a very close distance of 1 mm to the sample surface. The experiment was carried out in air at atmospheric pressure. In this configuration, the sample was ablated by a shockwave generated from the air breakdown plasma formed near the sample surface. Under this condition, we successfully obtained spectra of the resonance emission line for high concentration K (K I 766.4 nm and K I 769.9 nm) that are free from self-reversal and weakly affected by the self-absorption. Furthermore, the quantitative analysis results for the element K showed that a linear calibration curve over a wide concentration range could be achieved, which indicates the effectiveness of this technique in reducing the self-absorption effect and improving the analytical performance of ordinary single-pulse LIBS.

Analysis of powder samples available in small quantities has been carried out using metal-assisted gas plasma by utilizing a transversely excited atmospheric (TEA) CO2 laser. The powder was homogeneously mixed with Si grease, and the mixed powder was painted on a metal subtarget. When a TEA CO2 laser was directly focused on the metal subtarget at atmospheric pressure of He gas, a high-temperature He gas plasma was induced. It is assumed that the powder particles were vaporized to be effectively atomized and excited in the gas plasma region. This method has been employed in the rapid analyses of elements in organic and inorganic powder samples present in small quantities. Detection of trace elements of Cr and Pb has been successfully made by using the supplement powder and loam soil, respectively. The detection limits of Pb in loam soil were approximately 20 mg/kg.

Several experiments are performed to explore the possible benefits of using bamboo charcoal as a sample holder for rapid powder analysis using laser-induced breakdown spectroscopy at low-pressure helium ambient gas. Standard powdered samples such as ZnS and CuSO4 are used to demonstrate the feasibility of using cheap and widely available bamboo charcoal as a sample holder. A commercial baby milk powder and several sets of soil samples with a tiny amount of impurities are also introduced to show the potential application of bamboo charcoal as a powder holder. By appropriately adjusting the laser pulse energy and the thickness of the powder layer, we successfully obtained a spectrum that is free from the undesirable matrix effect. A remarkable result was obtained, even using a tiny amount of the powder sample. This proposed method is considered notably promising for the rapid analysis of the powder sample, especially with a very limited amount.

A series of experiments are conducted for the study of time-dependent variations of major emission from the metastable excited He generated in various experimental conditions. Different Nd:YAG laser pulse widths and pulse energies, as well as purity of the He gas, are employed for studying quenching effects including the use of a Cu target in an experimental condition for spectrochemical analysis. It is found that in all cases investigated, the metastable excited He atom (He*) associated with the triplet He I 587.5 nm emission line has the unquestionable dominance over another triplet emission line of He I 388.8 nm and the singlet He I 667.8 nm emission. Further analysis of the present data combined with the results of previous studies suggested that the energy transfer between He atoms via the Penning-like collision-induced energy transfer process has so far remained less than appropriately addressed. It is strongly argued and demonstrated in this work that this underlying physical process is likely the moving force leading to the repeated He ionizations responsible for the self-propelled multiple amplification of the triplet He I 587.5 nm emission intensity particularly at the early stage of the shock wave formation. This study has convincingly demonstrated that the Penning-like collision-induced energy transfer process can also effectively take place between He* and the ablated atoms, implying its usefulness for spectrochemical laser-induced plasma spectroscopy analysis.

A unique approach for achieving total suppression of the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) has been demonstrated employing a previously published technique of laser-induced plasma spectroscopy utilizing a helium (He) metastable excited state (LIPS-He*).This achievement was attained by the use of the He metastable excited state (He*) and a Penning-like energy transfer mechanism for the delayed excitation of the ablated analyte atoms. KCl and NaCl samples showed the disappearance of the self-absorption emission lines of K I 766.4 nm, K I 769.9 nm, Na I 588.9 nm, and Na I 589.5 nm, and the FWHM values of K I 766.4 and Na I 588.9 nm were found to be 0.8 nm and 0.15 nm, respectively, by LIPS-He* as compared to 4.8 nm and 1.4 nm, respectively, by single-laser operation. A standard Al sample also showed the total disappearance of the self-absorption emission lines Al I 394.4 nm and Al I 396.1 nm. The FWHM of Al I 396.1 nm was 0.12 nm when LIPS-He* was employed compared to 0.44 nm when a single laser was used. A remarkable linear calibration line with zero intercepts was also obtained for high-concentration Al samples (87.0%, 93.0% and 99.8%). Thus, it is established that the self-absorption effect can be completely neglected when excitation through He* is employed in LIBS.

A study is conducted on the detailed static and dynamic characteristics of plasma and the resulting emission spectral qualities generated by a femtosecond (fs) laser irradiation compared with those produced by nanosecond (ns) laser irradiation at a reduced ambient air pressure of 0.65 kPa. It is shown that both plasmas feature a tiny primary and a much larger secondary plasmas, which share the same hemispherical shape of roughly the same size at the appropriately chosen pulse energies. The resulted emission spectra in both cases exhibit one of the shock wave characteristics marked by a much stronger Zn triplet than its singlet emission lines. Further measurement of log(r)–log(t) of Cu I 521.8 nm emission line yields a slope of around 0.4, which is in good agreement with Sedov's equation derived for shock wave plasma. While exhibiting similar pressure-dependent emission intensities of Cu and Zn emission lines, the fs induced emission intensities are consistently lower than those induced by ns laser plasma. The estimated average temperature of the ns laser induced plasma (10 200 K) is only slightly higher than that induced by the fs laser (9800 K). The lower integrated emission intensity of fs plasma is related to previously reported lower electron density in fs laser-induced breakdown spectroscopy (fs-LIBS) and the faster decay of the associated continuum background, implying rapid diminution of ionized atoms and hence lower integrated emission intensity. Therefore, apart from cases demanding minimal surface damages, the simpler and less expensive ns-LIBS should be considered as a more favorable alternative for spectrochemical analysis. However, the applications to surface analysis do show that the fs laser offers higher detection sensitivity. A judicial selection is, therefore, strongly recommended.

A laser-induced-breakdown-spectroscopy (LIBS) experiment with a unique double-pulse setup and operated in low-pressure (3 kPa) He ambient gas is performed to study the detection of light elements, such as hydrogen (H) and deuterium (D), as well as elements of high excitation energies, such as fluorine (F) and chlorine (Cl), which are usually difficult to detect using ordinary LIBS techniques. A nanosecond Nd:YAG laser operated in its fundamental wavelength with energy of 54 mJ is focused onto the Al target to generate the He plasma. Another picosecond Nd:YAG laser operated in its fundamental wavelength with energy of 2 mJ is focused onto the sample surface and activated 2 μs before the operation of the nanosecond laser. The application to polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE) samples produces sharp and high-intensity Cl- and F-emission lines. Meanwhile, the sharp and well-resolved H-D-emission lines with merely 0.18 nm wavelength separation are also clearly detected from a zircaloy sample. Further measurement of a set of zircaloy samples containing different concentrations of D yields a linear calibration curve with a zero intercept. The detection limit of D is found to be about 10 ppm.

An experimental study has been performed on the gas pressure and laser energy dependent variations of plasma emission intensities in Ar, He and N 2 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.

Identification of major elements in milk liquid has been rapidly carried out by using pulse carbon dioxide (CO2) laser. Experimentally, a milk liquid was poured on a Cu metal plate to make a thin film on the metal surface. The liquid was then dried at 100°C for 5 minute. A thin film of milk liquid was produced with a thickness of around 0.1 mm. The Cu plate only functions as a metal subtarget. A pulse CO2 laser was irradiated on a metal surface to induce a luminous plasma. The atomization of liquid and excitation processes of atoms from the film sample happen in the plasma region. Various major elements in milk liquid, namely Ca, Mg, Na, and K can successfully be detected. Therefore, the method has high-prospect for major elemental analysis in liquid sample target.Identification of major elements in milk liquid has been rapidly carried out by using pulse carbon dioxide (CO2) laser. Experimentally, a milk liquid was poured on a Cu metal plate to make a thin film on the metal surface. The liquid was then dried at 100°C for 5 minute. A thin film of milk liquid was produced with a thickness of around 0.1 mm. The Cu plate only functions as a metal subtarget. A pulse CO2 laser was irradiated on a metal surface to induce a luminous plasma. The atomization of liquid and excitation processes of atoms from the film sample happen in the plasma region. Various major elements in milk liquid, namely Ca, Mg, Na, and K can successfully be detected. Therefore, the method has high-prospect for major elemental analysis in liquid sample target.

Taking advantages of the special characteristics of a transversely excited atmospheric (TEA) CO 2 laser, the analysis of sodium aerosol has been successfully conducted by using laser-induced gas plasma spectroscopy (LIGPS) method. In this study, the sodium aerosol was deposited on a nickel metal plate; the metal plate functions as a subtarget to initiate a gas plasma. When a pulsed TEA CO 2 laser was focused on the metal surface, a large-volume and high-temperature gas plasma was induced. The fine particles of sodium then entered into the gas plasma region to be dissociated and excited. By using this technique, a semi quantitative analysis of sodium aerosol was made. The detection limit of sodium was approximately 200 ppb.

Presented in this paper are the results of practical application of laser-induced breakdown spectroscopy to sensitive detection of rare earth elements (REEs) in trace amounts using a Cu subtarget supported stainless steel micro mesh (SSMM) powder sample holder. Powder samples containing separately a number of REEs (Yb, Y, Eu, and La) are measured using the SSMM sample holder and a 68 mJ ns Nd:YAG laser with −5 mm defocused irradiation in 1.3 kPa ambient air. All the resulted emission spectra are shown to exhibit excellent spectral quality featuring well resolved sharp spectral lines with low background and without spectral interference from the sample holder. Further measurements of additional powder samples with varied content of REEs are performed to reveal the existence of linear calibration lines with extrapolated zero intercept and well below 100 ppm detection limits promising for practical quantitative REEs analysis, particularly for sensitive field exploration of REEs.

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.

A comprehensive review of important progress achieved over the last 30 years regarding knowledge of laser-induced plasmas generated by CO2 and Nd:YAG lasers in a variety of ambient gases is presented in this article, as well as research results on the extension of laser-induced breakdown spectroscopy (LIBS) for quantitative analysis of light elements, especially hydrogen and deuterium. First, the formation of shock wave–induced expanding secondary plasma in low-pressure ambient gases is discussed along with the dynamic characteristics of the secondary plasma expansion process. The unique advantages of low-pressure gas plasma are explained in relation to the successful detection of the sharp H and D emission lines. The experimental results using helium ambient gas are presented with emphasis on the role of He gas plasma in introducing an additional delayed excitation mechanism involving the helium metastable excited state, which resulted in the complete resolution of H and D emission lines, separat...

This report presents the results of laser-induced breakdown spectroscopy (LIBS) study on biological and food samples of high water content using a picosecond (ps) laser at low output energy of 10 mJ and low-pressure helium ambient gas at 2 kPa. Evidence of excellent emission spectra of various analyte elements with very low background is demonstrated for a variety of samples without the need of sample pretreatment. Specifically, limits of detection in the range of sub-ppm are obtained for hazardous Pb and B impurities in carrots and meatballs. This study also shows the inferior performance of LIBS using a nanosecond laser and atmospheric ambient air for a soft sample of high water content and thereby explains its less successful applications in previous attempts. The present result has instead demonstrated the feasibility and favorable results of employing LIBS with a ps laser and low-pressure helium ambient gas as a less costly and more practical alternative to inductively coupled plasma for regular high sensitive inspection of harmful food preservatives and environmental pollutants.

Our previous work on an innovative method of hydrogen (H) analysis using the specific characteristics of a TEA CO2 laser, “selective detection method of H”, has been improved to realize a high H sensitive analysis with a detection limit of several µg/g. For this purpose, first, we clarified the origin of the H emission disturbance coming from H2O molecules; namely, we showed that most of the H emission came from H2O on the metal surface and not from H2O existing in the surrounding gas when we formed a laser-induced gas plasma. Second, the difference in the emission characteristics between the H emission from H2O on the metal surface and H emission from inside in sample was studied to determine the optimum gating time of the optical multi-channel analyzer (OMA). Third, the gas plasma was totally covered by fresh helium gas using a big pipe (5 mm in diameter) and by flowing a high amount of He (10 l/min). Also, we demonstrated that our methods could potentially be applied to H analysis in steel samples, where an H analysis with a sensitivity of less than 1 µg/g is required without employing a heating process, by removing H2O on the sample surface with the aid of defocused TEA CO2 laser irradiation. Thus, we stress that our method can be used for a highly sensitive, in-situ analysis of H for metal samples.

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.