Maria Margaretha Suliyanti

Characteristics of a laser plasma induced by irradiation of a normal-oscillation YAG laser at low pressures

The generation of a laser-induced shock wave plasma in air at reduced pressure was achieved by focusing a normal-oscillation Nd:YAG laser on a brass sheet. The characteristics of the plasma were analysed under three different conditions: free expansion of the plasma, confinement of the plasma by limiting the plasma region using two parallel glass plates and interruption of the plasma by placement of a wedge in front of the plasma, in order to interrupt the expansion of the plasma. Spatially and temporally integrated methods were also developed in order to develop a more detailed understanding of the excitation mechanism of the plasma. Furthermore, a new technique of shadow graphing which involves the use of a He - Ne laser as a probe light was also developed as well as a measurement of the time profile of the temperature. By using this new method the relationship between the density jump and the starting point of atomic emission was detected simultaneously. The results show that the plasma was also generated by the shock wave as for the case of the short-pulse laser (Q switched). The extremely low ion and background emission, as low as compared with neutral emission, makes this plasma potentially useful for spectrochemical analysis.

Subtarget Effect on Laser Plasma Generated by Transversely Excited Atmospheric CO2 Laser at Atmospheric Gas Pressure.

An experimental study has been carried out on the dynamical process taking place in the laser plasma generated by Transversely Excited Atmospheric CO2 laser (100 mJ, 50 ns) irradiation of a soft sample at surrounding helium pressure of 1 atm. It is shown that the presence of a copper subtarget behind the soft sample is crucial in raising the gushing speed of the atoms to the level adequate for the generation of shock wave laser plasma even at atmospheric pressure. It is also found that the time profiles of spatially integrated emission intensity of the targets atoms and gas atoms exhibit a characteristic dynamical process that consists of successive excitation and cooling stages even at such a high pressure, which is typical of shock wave laser plasma. It is therefore suggested that the generation of the laser plasma at atmospheric pressure is more likely due to the shock wave mechanism than to the widely known breakdown mechanism. Initial spectrochemical analysis of water from the blow off of a boiler system was also carried out, showing a detection limit of as low as 5 ppm for calcium.

Preliminary analysis of C and H in a Sangiran fossil using laser-induced plasma at reduced pressure

A Nd:YAG laser (1064nm, 120mJ, and 8ns) was focused on various types of fossil samples, including fossilized buffalo horns (around 400 000 and 1×106yr old, respectively) found in Sangiran, Indonesia. Such fossils represent an important starting point for tracing man’s origin and evolution during the Pleistocene era. Carbon emission was found to decrease significantly with the degree of fossilization and no carbon emission was found in a horn fossil dated at 1×106yr. Some molecular band spectra were also found in all the fossils examined in this study. It was assumed that by combining information on carbon emission, hydrogen emission, and molecular band spectra that the degree of fossilization might be quantitatively calculated. Further results showed that silicon emission is not detected in old fossils, but it is present as a major constituent. This is probably due to the fact that silicon is strongly bound to other elements in old fossils and is ablated in the form of clusters. In order to prove the abov...

The role of He in enhancing the intensity and lifetime of H and D emissions from laser-induced atmospheric-pressure plasma

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 Hα and Hβ 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 S10 metastable state, which was also responsible for the delayed excitation of H and D atoms via an energy transfer mechanism involving a Penning-...

Detection of deuterium and hydrogen using laser-induced helium gas plasma at atmospheric pressure

An experimental study on gas analysis by means of laser-induced breakdown spectroscopy was conducted using a Nd-yttrium aluminum garnet laser (1,064 nm, 120 mJ, 8 ns) and helium host gas at atmospheric pressure on a sample of mixed water (H2O) and heavy water (D2O) in vapor form. It was shown that completely resolved hydrogen (Hα) and deuterium (Dα) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that the helium metastable excited state plays an important role in the hydrogen excitation process.

Application of primary plasma standardization to Nd-YAG laser-induced shock wave plasma spectrometry for quantitative analysis of high concentration Au–Ag–Cu alloy

Abstract A study was performed on a laser-induced shock wave plasma generated on high concentration Au–Ag–Cu alloys by a Q-switched Nd-YAG laser of 4.8 mJ under reduced air pressure of 2 torr. It was found that the total emission intensity of the secondary plasma is proportional to the intensity of the primary plasma. Assuming linear proportionality between the intensity of the primary plasma and the number of atoms vaporized from the target, it is proposed that quantitative analysis can be applied to the intensities of the analytical emission lines normalized by the total intensity of the primary plasma. This experimental result demonstrated for each metal element shows an excellent linear relationship between the normalized emission line intensity and the content of the corresponding element.

Quenching of He-induced intensity enhancement effect in H and D emission produced by Nd-doped yttrium aluminum garnet laser irradiation on solid targets in low pressure helium gas

An experimental study was performed on the N2-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 dis...

Intensity distributions of enhanced H emission from laser-induced low-pressure He plasma and a suggested He-assisted excitation mechanism

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...

Study of Hydrogen and Deuterium Emission Characteristics in Laser-Induced Low-Pressure Helium Plasma for the Suppression of Surface Water Contamination

An experimental study was conducted in search of the experimental condition required for the much needed suppression of spectral interference caused by surface water in hydrogen analysis using laser-induced low-pressure helium plasma spectroscopy. The problem arising from the difficulty in distinguishing hydrogen emission from hydrogen impurity inside the sample and that coming from the water molecules was overcome by taking advantage of similar emission characteristics shared by hydrogen and deuterium demonstrated in this experiment by the distinct time-dependent and pressure-dependent variations of the D and H emission intensities from the D-doped zircaloy-4 samples. This similarity allows the study of H impurity emission in terms of D emission from the D-doped samples and thereby separating it from the H emission originating from the water molecules. Employing this strategy has allowed us to achieve the large suppression of water induced spectral interference from the previous minimum of 400 microg/g to the current value of 30 microg/g when a laser beam of 34 mJ under tight focusing condition was employed. Along with this favorable result, this experimental condition has also provided a much better (about 6-fold higher) spatial resolution, although these results were achieved at the expense of reducing the linear calibration range from the previous 4 300 microg/g to the present 200 microg/g.

Plasma emission induced by an Nd-YAG laser at low pressure on solid organic sample, its mechanism, and analytical application

An Nd-YAG laser (1064 nm, 120 mJ, 8 ns) was focused on various types of solid organic samples such as a black acrylic plate, a black polyvinyl chloride plastic sheet, and a methoxy polyaniline film coated on the surface of a glass substrate, under a surrounding air pressure of 2 Torr. A modulated plasma technique was used to study the mechanism of excitation of the emission of the organic material. As a result, we conclude that ablated atoms and molecules are excited by a shock-wave mechanism, similar to the case of hard samples such as metal. The ablation speed of hydrogen emission (H I 656.2 nm) was examined and the results show that the release speed of the ablated atoms is relatively low (less than Mach 10) and persists for a longer period of time (around 1 μs); this phenomenon can be understood by assuming that the soft target absorbs recoil energy, causing a low release speed of ablated atoms which would form the shock wave. This was overcome by placing a subtarget on the back of the soft sample so ...