Hery Suyanto

Shock Excitation and Cooling Stage in the Laser Plasma Induced by a Q-Switched Nd:YAG Laser at Low Pressures

An experimental study has been carried out on the dynamical process taking place in the secondary plasma generated by a Q-switched Nd:YAG laser (80 mJ, 8 ns) on a copper target at reduced pressure. Accurate dynamical characterization of the cross-sectional view of the plasma has been made possible by the unique combination of a plasma confinement configuration and the time-resolved measurement technique. In addition to reaffirming the role of the blast-wave mechanism in the generation of secondary plasma, an analysis of the time-resolved spatial distributions of emission intensities and the time-resolved spatial distributions of temperature was made. As a result, the occurrence of two-stage emission processes, the “shock excitation stage” and “cooling stage,” has been proved. For instance, at 2 Torr it is shown that the emission process is initiated by a brief shock excitation process (∼ 1 μs) and followed by a longer cooling process (∼ 3 μs). The experimental results concerning the characteristics of the plasma can be well understood by considering the two-stage processes.

Hydrogen emission by Nd-YAG laser-induced shock wave plasma and its application to the quantitative analysis of zircalloy

An experiment was carried out to demonstrate the detection of a hydrogen emission line, HI656.2nm (Hα), in a plasma induced by a Q-switched Nd-YAG (YAG, yttrium aluminium garnet) laser in a low pressure gas on various types of samples, such as zinc, a glass slide, and a zircalloy tube. Contribution by surface water could be suppressed by a laser cleaning treatment and the resulting calibration curve obtained for zircalloy tube samples doped with various concentrations of hydrogen (0, 200, 540, and 960) suggest potential applications to the quantitative analysis of hydrogen. A study of the dynamic process represented by the time profiles of the hydrogen emission, in comparison with those for zinc atomic emission, revealed a specific feature that is related to the small mass of hydrogen. This specific feature can be explained by the shock wave excitation mechanism in terms of new hypothetical process, namely, a mismatch between the movement of ablated hydrogen atoms and the formation of the shock wave.

Characteristics of Hydrogen Emission in Laser Plasma Induced by Focusing Fundamental Q-sw YAG Laser on Solid Samples

Hydrogen emission has been studied in laser plasma by focusing a Nd-YAG laser (1,064 nm, 50 mJ, 8 ns) on various types of samples, such as copper plate, zinc plate and glass plate. Several parameters influencing the emission were varied, such as the type of gas (air, nitrogen and helium), gas pressures (ranging from 2 up to 760 Torr) and laser power density. It was found that Hα emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in the low-pressure region. It was also confirmed that the conventional well-known laser-induced breakdown spectroscopy (LIBS), which usually carried out at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. This specific characteristic of the pressure dependence of hydrogen is interpreted based on our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host elements.

Spectral and Dynamic Characteristics of Helium Plasma Emission and its Effect on a Laser-Ablated Target Emission in a Double-Pulse Laser-Induced Breakdown Spectroscopy (LIBS) Experiment

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 (1s 1 3d 1 ). 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.

Hole-Modulated Plasma for Suppressing Background Emission in Laser-Induced Shock Wave Plasma Spectroscopy

An experimental study has been carried out on the dynamical process taking place in the partially confined secondary plasma generated by a Q-switched Nd-YAG laser (47 mJ, 8 ns) focused into a small hole of proper size on a zinc plate in a surrounding air of reduced pressure. The undesirable continuum emission from the primary plasma is effectively kept within the hole, away from the expanding secondary plasma, and enhances the detection sensitivity of the plasma emission in elemental analysis. The simultaneous detection of density jump and emission of Zn I 481.0 nm and the time profile of averaged temperature in the expanding plasma support the scenario of the shock wave excitation mechanism, which has been proposed by the present authors.

Quantitative and sensitive analysis of CN molecules using laser induced low pressure He plasma

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 μg/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.

Excitation mechanisms in 1 mJ picosecond laser induced low pressure He plasma and the resulting spectral quality enhancement

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...

Water Analysis by Laser-Induced Shock Wave Plasma Spectroscopy Using Re-crystallized KBr Powder Confined in a Cylindrical Tube

It has been demonstrated that shock wave plasma is produced even for a powder sample when a Q-sw Nd:YAG laser beam was focused at a reduced pressure on the surface of powder confined in a small vertical hole. KBr powder was dissolved in the water to be analyzed, and the water was boiled. The re-crystallized KBr, which consisted of trapped impurities present in the water, was contained in the hole to be irradiated by the laser pulse at low pressure.

H-D Analysis Employing Low-Pressure microjoule Picosecond Laser-Induced Breakdown Spectroscopy

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.

Laser-Induced Breakdown Spectroscopy (LIBS) for spectral characterization of regular coffee beans and luwak coffee bean

Luwak (civet) coffee refers to a type of coffee, where the cherries have been priorly digested and then defecated by a civet (Paradoxurus Hermaphroditus), a catlike animals typically habited in Indonesia. Luwak will only selectively select ripe cherries, and digesting them by enzymatic fermentation in its digestive system. The defecated beans is then removed and cleaned from the feces. It is regarded as the world’s most expensive coffee, Traditionally the quality of the coffee is subjectively determined by a tester. This research is motivated by the needs to study and develop quantitative parameters in determining the quality of coffee bean, which are more objective to measure the quality of coffee products. LIBS technique was used to identify the elemental contents of coffee beans based on its spectral characteristics in the range 200-900 nm. Samples of green beans from variant of arabica and robusta, either regular and luwak, were collected from 5 plantations in East Java. From the recorded spectra, intensity ratio of nitrogen (N), hydrogen (H), and oxygen (O) as essential elements in coffee is applied. In general, values extracted from luwak coffee bean is higher with increases 0.03% - 79.93%. A Discriminant Function Analysis (DFA) also applied to identify marker elements that characterize the regular and luwak beans. Elements of Ca, W, Sr, Mg, and H are the ones used to differentiate the regular and luwak beans from arabica variant, while Ca and W are the ones used to differentiate the regular and luwak beans of robusta variant.