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"ABSTRACTA comprehensive study has been made on the dynamical process taking place in the laser-plasma generation i.nduced by a TEA CO2 laser bombardment on metal target and non-metal target Eom low to high pressures surrounding gas. ln the case of metal target, pure zinc plate was used as a target and bombarded with 400 ml laser pulse energy. Dynamical characterization of plasma expansion and excitation were examined in detail both for target atomic emission (Zn I 481.0 nm) and gas atomic emission (He I 587.6 nm) by using an unique time-resolved spatial distribution measurement and conventionalemission spectroscopic detection method. The resultsshowed that the plasma expands and develops with time. The mechanism of plasma generation can be classified into three cases depending on the surrounding gas pressures; target shock wave plasma in the pnessure range between 2 Torr and 20 Torr, coupling shock wave plasma in the pressure range between S0 Torr and 200 Torr and gas ?break down shock wave plasma in the pressure range between 200 Torr and 1 atm. In all cases in the laser-plasma generation under TEA CO; laser bombardment on metal target, shock wave process-always plays important role forexciting the target atoms and gas molecules.ln the case of , non-metal target, a museum glass was used as a target and bombarded with a 400 mJ laser; pulse energy By using the conventional emission spectroscopic detection method, namely temporally and spatially integrated and time-resolved spatially integrated of plasma emission, it was shown that the plasma mainly consists of target atomic emission. Only weak gas atomic emission intensity could be observed even at 1 atm of surrounding gas pressure. These results indicate that the gas breakdown is not a major process responsible to the plasma formation even at high pressure surrounding gas. Shock wave process was considered as animportant role in this plasma formation. By the use of shadowgraph technique to detect the density jump signal due to the shock wave front involving a He-Ne laser as a probe light, simultaneous detection of the shock wave Bent and the emission iiont was successfully implemented. The result showed that at the initial stages of plasma expansion shock wave 'dont and emission front coincide and move together with time. At the later stages of plasma expansion the two fronts become separate with the emission front left behind the shock wave front. These results are completely coinciding with the shock wave plasma model. Unfortunately, in this experiment we succeed to detect the density jump signal only for high pressure surrounding gas, above 100 Torr. At the pressures lower than 100 Torr the density jump signal was very weak and it is diflicult to distinguish with the noise including in the signal.The other important experimental results that support the shock wave plasma model were also obtained in this experiment, namely the coincidence of emission iziont regardless of their atomic weight and sub-target effect. By using lead glass as a sample, which contain Pb, Si, and Ca, it was confirmed that the emission front of the Pb 1450.8 nm, Si I 288.2 nm and Ca I 422.6 nm almost coincide regardless of their atomic weight. This result also supports the shock wave plasma model because, by the stagnation of the propelling atoms, the front position of the all atoms coincides regardless of its mass. In the case of sub-target effect, we confirmed that plasmacould be produced even for sch target if sub-target is set behind the sample. In this case we use a sample as a sub-target and a vinyl tape was attached to the quartz sample as a target. The TEA CO2 laser bombardment was used at 150 mJ and at 1 atm of air. The main role ofthe subtarget is to produce a repulsion force for atom gushing with high speed. For shock wave, high speed is necessary condition to compress the gas.Coincidence of the movement of the shock wave iiiont and the emission front in the initial stages of plasma expansion is a direct proof of the shock wave plasma model. By improving the detection technique of the density jump associated with the shock wave, the correlation between the shockwave fiont and the emission front was examined in detail. For this purpose rainbow interferometer system, which has higher sensitivity compared with the shadowgraph technique, was used to detect the density jump signal. We succeed to realize simultaneous detection of shock wave front and emission front iiom 3 Torr until 1 atm of air when a quartz sample is bombarded with a 600 mJ TEA CO2 laser. In all pressure that were examined, the shock wave front and the emission front always coincide and move together with time in the initial stages and separate at the later stages with emission front left behind the shock wave tiont. The coincidence of the shock wave iiont and emission front and move together with time at the initial stages of plasma expansion was also obtained by using ruby as a sample at 10 Torr and 100 Torr of air as well as with museum glass at the same laser pulse energy."

"ABSTRACT

A series of experimental studies on the emission spectra of laser-induced plasma at reduced ambient gas pressure were carried out for the analyses of organic materials. The plasma was generated by means of a Q-switch Nd-YAG laser having a pulse width of 8 ns, wavelength of 1,064 nm and operated at an energy of 120 mJ. The emission was detected with time-integrated and time resolved spectroscopic techniques. These studies were intended to investigate the possible extension of the previously established technique of laser induced shock-wave plasma spectroscopy (LISPS) for its applications to organic samples of different natures as well as to examine the related excitation mechanism and the effects of different experimental conditions on the plasma generation.

The first experiment was conducted on soft solid organic samples or samples which have low melting point. It is well known that plasma emission from soft organic samples can not be directly produced by Nd-YAG laser irradiation even in low pressure surrounding gas. We have shown in this experiment that this problem can be overcome by placing a hard sub-target behind or underneath the soft samples or putting an obstacle in front of it. The sharp emission lines of light elements such as hydrogen, carbon and chlorine from organic samples were clearly observed from a black polyvinyl chloride plastic sheet when the shock wave plasma was generated in appropriately chosen low-pressure of the ambient air.

In the second experiment, the same technique has been successfully applied for hydrogen and carbon atomic emission analysis in various fossil samples at low gas pressure around 3 Torr. The quality of the spectrum allows a quantitative comparison of the carbon and hydrogen emission intensities with the associated molecular band spectra, yielding a rough estimation of the period of fossilization process. In the third experiment, another successful application of this technique was also achieved for spectrochemical analysis of bead samples, which offers the possibility of its applications for non destructive identifications of genuine beads as well as its potential application to other areas of forgery inspection.

In addition to the variety of applications demonstrated in those experiments, the related study has also verified the distinct role of laser induced shockwave in the generation of excitation process leading to the observed favorable plasma emission. We show in this connection the crucial condition of low pressure ambient gas for producing the sharp emission lines desirable for high resolution and quantitative analysis. It was further demonstrated that the mass difference between the host elements and the impurity elements has a sensitive effect on the pressure dependent characteristics of the emission lines to be analyzed.

On the basis of those results, we have reason to hold out hope for the extension of the technique developed in this study to more credible quantitative spectrochemical analysis of organic samples, including those of biomedical interest and those in the form of thin films."

"ABSTRACT

A series of experimental studies on the emission spectra of laser-induced plasma at reduced ambient gas pressure were carried out for the analyses of organic materials. The plasma was generated by means of a Q-switch Nd-YAG laser having a pulse width of 8 ns, wavelength of 1,064 nm and operated at an energy of 120 mJ. The emission was detected with time-integrated and time resolved spectroscopic techniques. These studies were intended to investigate the possible extension of the previously established technique of laser induced shock-wave plasma spectroscopy (LISPS) for its applications to organic samples of different natures as well as to examine the related excitation mechanism and the effects of different experimental conditions on the plasma generation.

The first experiment was conducted on soft solid organic samples or samples which have low melting point. It is well known that plasma emission from soft organic samples can not be directly produced by Nd-YAG laser irradiation even in low pressure surrounding gas. We have shown in this experiment that this problem can be overcome by placing a hard sub-target behind or underneath the soft samples or putting an obstacle in front of it. The sharp emission lines of light elements such as hydrogen, carbon and chlorine from organic samples were clearly observed from a black polyvinyl chloride plastic sheet when the shock wave plasma was generated in appropriately chosen low-pressure of the ambient air.

In the second experiment, the same technique has been successfully applied for hydrogen and carbon atomic emission analysis in various fossil samples at low gas pressure around 3 Torr. The quality of the spectrum allows a quantitative comparison of the carbon and hydrogen emission intensities with the associated molecular band spectra, yielding a rough estimation of the period of fossilization process. In the third experiment, another successful application of this technique was also achieved for spectrochemical analysis of bead samples, which offers the possibility of its applications for non destructive identifications of genuine beads as well as its potential application to other areas of forgery inspection.

In addition to the variety of applications demonstrated in those experiments, the related study has also verified the distinct role of laser induced shockwave in the generation of excitation process leading to the observed favorable plasma emission. We show in this connection the crucial condition of low pressure ambient gas for producing the sharp emission lines desirable for high resolution and quantitative analysis. It was further demonstrated that the mass difference between the host elements and the impurity elements has a sensitive effect on the pressure dependent characteristics of the emission lines to be analyzed.

On the basis of those results, we have reason to hold out hope for the extension of the technique developed in this study to more credible quantitative spectrochemical analysis of organic samples, including those of biomedical interest and those in the form of thin films."

"A TEA CO2 laser pulse (50 mJ, 100 ns) was focused under reduced pressure on the silicone grease painted on copper plate as a sub-target with a power density of 6 GW/cm2. The comparison was made on the characteristics of the induced laser plasma between the two cases, with sub-target and without sub-target. It is proved that emission spectrum assigned to silicone atom can be detected only for the case with sub-target. It is also proved that in the absence of the sub-target, the gushing speed of the atoms is very low, while for the case with sub-target, the gushing speed of atoms becomes very fast. It is shown that the setting of sub-target is very effective to make laser-induced shock-wave plasma and it is very effective to realize quantitative analysis of soft material."

"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 the quantitative analysis can be applied to the intensities of the analytical emission Iines 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 corresponding element after primary plasma normalization."

"The role of shock wave in the generation of laser induced secondary plasma was first suggested by Kagawa et al. from an experimental result employing N2 laser on metal targets at reduced surrounding air pressure. This so-called shock wave induced plasma model has since been reexamined and confirmed in a series of experiments performed by Kurniawan and Kagawa et al. using TEA (Transversely Excited Atmospheric) CO2 laser and XeCI excimer laser. All of these experiments were performed at reduced gas pressures. The most important characteristics revealed by those experiments consist of the typical hemispherical shape of the plasma with a thin emission shell at the plasma front, which moves with a propagation length proportional to t°-4, in excellent agreement with the shock wave characteristics predicted theoretically by Sedov. It was further demonstrated that ionic emission was generally insignificant compared to neutral atom emission. While those results have provided relatively solid and comprehensive supports for the model, additional evidence on the density jump characteristic of shock wave generation and other on some unique aspect concerning interaction of shock wave with an object will still be desirable for further clarification on the role of the model.A series of experiment have been carried out on the dynamical process taking place in the secondary plasma induced by normal oscillation and Q-switched Nd-YAG (yttrium aluminum garnet) laser on brass, copper and zinc targets at reduced air pressures. Accurate dynamical characterization of the cross-sectional view of the plasma expansion has been made possible by the unique confinement technique using two parallel glass plates. In order to detect the shock front and the emission front simultaneously, a new shadowgraph technique involving a He-Ne laser as a light probe was also developed. Furthermore in an experiment intended for giving support to the shock wave excitation model qualitatively, the plasma was forced to collide with a wedge placed in front of the target in order to examine the reflection and diffraction phenomena. Measurements were also performed on the time-profile of the plasma emission to provide a description of the plasma temperature variation with time. The study was further substantiated by measurement of the time-resolved spatial distributions of emission intensities.The results showed that the plasma was generated through the shock-wave and the dynamical process of the secondary plasma is divided into two stages, namely, the "shock excitation stage" and the "cooling stage". During the shock excitation stage, the atoms gushing out from the target were adiabatically compressed against the surrounding gas, resulting in a rapid rise of the plasma temperature up to around 9,000 K. For the case of 2 Ton gas pressure, with the laser pulse of 86 m7 targeted on copper sample, the shock excitation stage lasted for about 1 µs, which was followed immediately by the cooling stage and the plasma temperature decreases gradually to around 7,500 K in about 3 .is. The excitation stage and the cooling stage periods became longer with increasing laser pulse energy.The multiple excitation processes associated with the secondary plasma emission, and generated by successive multiple shock wave, was clearly observed when the normal oscillation laser was focused onto the surface of the target. The emission characteristics of this secondary plasma showed an extremely low ion and background emissions. This condition is suitable for highly sensitive spectrochemical analysis, as the temperature of the plasma is still high enough (around 7,000 K) for the excitation of neutral atoms. Another favorable conditions is the large amount of material ejected in the process (amounting to 10 µg), which permits an average analysis.For a practical consideration, the condition to increase sensitivity by suppressing the background was also studied. The result showed that the sensitivity of laser induced shock wave plasma spectroscopy could be increased by reducing laser pulse energy, in which the less expensive time-integrated detection method can be applied. On the other hand, when the sample requires a high power laser beam, the sensitivity could also be enhanced with the aid of a time-gated DMA (Optical Multi channel Analyzer) system by cutting-off the ionic emission coming from the shock excitation stage."

"A special interferometric technique with high sensitivity has been devised on the basis of rainbows refractometer without the use of an additional and delicate amplitude-splitting setup. This new technique was use for the characterization of shock wave plasma induced by a Q-sw Nd-YAG laser on various kinds of metal samples under reduced gas pressures. An unmistakable signal of density jump was detected simultaneously with the emission front signal. It is proved that at the initial stage of the secondary plasma expansion, the front of the emission and the front of the blast wave was coincide and move together with time. However, at a later stage, the front of the emission will separate from that of the blast wave induced in the surrounding gas at low pressures. Using Cu and Zn samples, the experimental result showed that the separation of the emission front and blast wave front took place at 4 mm above sample surface for the laser energy of 140 mJ."

"ABSTRACTAn comprehensiove study has been carried out for the study and extension of lases induce shock wave plasma spectroscopy (LISPS) application to non metalic soft and hard samples. For this purpose, a series of experiments were conducted to investigate the dynamical process taking place in the laser plasma generated by a high power and short pulse laser irradiations on a non metal soft and hard samples it was found that in the case of non metal soft sample, the ablated atoms failed to induce a visible plasma at the surface of the target however, it became possible, after a few laser shots depending on the target layer thickness, to generate the sock wave plasma emitting the characteristic spectral line of the target material.Another related phenomenon studied in this experiment is the pre-irradiation effect pbserved on a non metal hard sample such as quartz sample, which was characterized by absence of secondary plasma at athe initial shots. The disappearance of this effect at a later stage was found to be connected with the appearance of a crater of appropriate depth on the sample surface created by iniatial repeated irradiations on the sample surface. The plasma produced thereafter exhibited typical features of a secondary plasma. Further experiment employing aaratificial ring crater on the sample surface has eliminated the pre-irraduation effect completely, and has thus demonstrated that it is the confinenement effect of the crater which was solely responsible for the generation of secondary plasma from the non metal hard tearget. This conclusion is ini confrormation with the shock wave proposed earlier.These experimental studies have thus considerably substantiated our understanding of the process of secondary plasma generatuion. In turn, this result helps to improve the quality and extend the scope of LISPS applications in the future"

"ABSTRACTAn comprehensiove study has been carried out for the study and extension of lases induce shock wave plasma spectroscopy (LISPS) application to non metalic soft and hard samples. For this purpose, a series of experiments were conducted to investigate the dynamical process taking place in the laser plasma generated by a high power and short pulse laser irradiations on a non metal soft and hard samples it was found that in the case of non metal soft sample, the ablated atoms failed to induce a visible plasma at the surface of the target however, it became possible, after a few laser shots depending on the target layer thickness, to generate the sock wave plasma emitting the characteristic spectral line of the target material.Another related phenomenon studied in this experiment is the pre-irradiation effect pbserved on a non metal hard sample such as quartz sample, which was characterized by absence of secondary plasma at athe initial shots. The disappearance of this effect at a later stage was found to be connected with the appearance of a crater of appropriate depth on the sample surface created by iniatial repeated irradiations on the sample surface. The plasma produced thereafter exhibited typical features of a secondary plasma. Further experiment employing aaratificial ring crater on the sample surface has eliminated the pre-irraduation effect completely, and has thus demonstrated that it is the confinenement effect of the crater which was solely responsible for the generation of secondary plasma from the non metal hard tearget. This conclusion is ini confrormation with the shock wave proposed earlier.These experimental studies have thus considerably substantiated our understanding of the process of secondary plasma generatuion. In turn, this result helps to improve the quality and extend the scope of LISPS applications in the future"

"Perkembangan teknologi menuntut pembaruan di berbagai bidang, salah satunya bidang keamaanan. Di antaranya, terdapat pengembangan pemanfaatan laser di dalam air. Dalam pengembangan sistem deteksi berbasis cahaya laser, diperlukan berbagai data mengenai sifat cahaya laser di dalam air yang mana akan diteliti dalam buku skripsi ini. Jenis laser yang digunakan adalah laser gas Helium-Neon dengan panjang gelombang 632 nm dan daya 30 mW. Penelitian dilakukan dengan menganalisis daya terukur dari laser sebelum dan setelah terjadi propagasi serta pemantulan pada akuarium yang berisikan air dengan berbagai tingkat salinitas. Hal-hal yang dikaji pada penelitian ini adalah karakteristik propagasi laser dan rugi-rugi daya laser. Tahap berikutnya adalah menyusun jaring-jaring laser dengan arah propagasi cahaya horizontal, tegak lurus dinding akuarium. Selanjutnya pada posisi terakhir berkas cahaya digunakan detektor LDR, yang menggunakan Arduino UNO sebagai mikrokontrolernya. Rangkaian tersebut memberikan peringatan berupa suara buzzer dan kedipan LED merah ketika jaring-jaring laser Helium-Neon tidak terdeteksi oleh LDR. Dari hasil eksperimen diperoleh bahwa rugi-rugi daya laser untuk jaring-jaring horizontal berkisar antara 33,16% sampai 73,19%; dengan rugi-rugi lebih tinggi terjadi ketika berkas laser berpropagasi menembus akuarium. Dari hasil perhitungan diperoleh nilai absorptivitas air dengan salinitas 35 ppt adalah 0,00962 L mol-1cm-1, nilai ini merupakan nilai dengan error terkecil pada perhitungan. Dengan pengembangan lebih lanjut, diharapkan hasil riset ini dapat diaplikasikan untuk membangun sistem pendeteksi obyek di dalam air.

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Technological developments demand updates in various fields, one of which is security. Among them is the development of the use of lasers in water. In developing a laser light-based detection system, various data regarding the properties of laser light in water are needed, which will be examined in this thesis. The type of laser used is a Helium-Neon gas laser with a wavelength of 632 nm and a power of 30 mW. The research was conducted by analyzing the measured power of the laser before and after propagation and reflection occurred in an aquarium containing water with various levels of salinity. In this work, the characteristics of laser propagation and laser power losses were studied, followed by the arrangement of the laser mesh with the light propagation direction horizontal, perpendicular to the aquarium wall. Furthermore, in the last position of the light beam, an LDR detector is used, which uses an Arduino UNO as the microcontroller. The circuit gives a warning in the form of a buzzer and red LED flashes when the Helium-Neon laser mesh is not detected by the LDR. From the experimental results, it was found that the laser power losses for horizontal mesh ranged from 33.16% to 73.19%; with higher losses occurring when the laser beam propagated through the aquarium. From the calculation results, the absorptivity value of water with a salinity of 35 ppt is 0.00962 L mol-1cm-1, this value is the value with the least error in the calculation. With further development, it is hoped that the results of this research can be applied to build an object detection system in water."