• Journal of Welding and Joining
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• v.25 no.3
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

• Journal of the Korean Society of Combustion
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• v.9 no.3
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• pp.27-35
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• 2004

Diode laser absorption sensors are advantageous because they may provide fast, sensitive, absolute, and selective measurements of species concentration. These systems are very attractive for practical applications owing to its compactness, resonable cost, robustness, and ease of use. In addition, diode lasers are fiber-optic compatible and thus enable simultaneous measurements of multiple species along a line-of-sight. Recent advances of room-temperature, near-IR and visible diode laser sources for telecommunication, optical data storage applications make it possible to be applied for combustion diagnostics based on diode laser absorption spectroscopy. Therefore, combined with fiber-optics and high sensitive detection strategies, compact and portable sensor systems are now appearing for variety of applications. The objectives of this research are to develope a new gas sensing system and to verify feasibility of this system. Wavelength and power characteristics as a function of injection current and temperature are experimentally found out. Direct absorption spectroscopy has been demonstrated in these experiments and has a bright prospect to this diode laser system.

• Journal of the Korean Vacuum Society
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• v.16 no.2
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• pp.116-121
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• 2007

TiNi shape memory alloy(SMA) was fabricated by PLD(plused laser deposition) using equiatomic TiNi target. Composition and crystallization of TiNi thin films which were fabricated in ambient Ar gas(200m Torr)and vacuum($5{\times}10^{-6}\;Torr$) were investigated. Composition of TiNi thin films was characterized by energy-dispersive X-ray spectrometry (EDXS) and crystallization was confirmed by X-ray diffraction (XRD). The composition of films depends on the distance between target and substrate but does not sensitively depend on the substrate temperature. It is found that the composition of films can be easily controlled when substrate is placed inside plume in ambient Ar gas. It is also found that the in situ crystallization temperature ($ca.\;400^{\circ}C$) in ambient Ar gas is lowered in comparison with that of TiNi film prepared under vacuum. The low crystallization temperature in ambient Ar gas makes it possible to prepare the crystalline TiNi thin film without contamination.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.57-60
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• 2000

In this paper, it is purpose to develop a pulsed $CO_2$ laser with stable output at pulse repetition rate range of 2 KHz. We used a IGBT as a switching device. The laser cavity was fabricated as an axial and water cooled type. It was used a ring blower to increase a cooling effect The laser performance characteristics as parameters, such as pulse repetition rate, gas pressure have been investigated. The experiment was done under 3 electrode-type instead of 2 electrode-type. To achieve 3 electrode-type, we used two pulse-transformers which is operated parallel. As a result, the maximum output was about 28 W at the total pressure of 20 Torr, the gas mixture $Co_2$:$N_2$:He=1:9:15 and the pulse repetition rate of 1300 Hz.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.185-185
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• 2011

ZnTe semiconductor is very attractive materials for optoelectronic devices in the visible green spectral region because of it has direct bandgap of 2.26 eV. The prototypes of ZnTe light emitting diodes (LEDs) have been reported [1], showing that their green emission peak closely matches the most sensitive region of the human eye. Another application to photovoltaics proved that ZnTe is useful for the production of high-efficiency multi-junction solar cells [2,3]. By using the pulse laser deposition system, ZnTe thin films were deposited on ZnO thin layer, which is grown on (0001) Al2O3substrates. To produce the plasma plume from an ablated ZnO and ZnTe target, a pulsed (10 Hz) YGA:Nd laser with energy density of 95 mJ/$cm^2$ and wavelength of 266 nm by a nonlinear fourth harmonic generator was used. The laser spot focused on the surface of the ZnO and ZnTe target by using an optical lens was approximately 1 mm2. The base pressure of the chamber was kept at a pressure around $10^{-6}$ Torr by using a turbo molecular pump. The oxygen gas flow was controlled around 3 sccm by using a mass flow controller system. During the ZnTe deposition, the substrate temperature was $400^{\circ}C$ and the ambient gas pressure was $10^{-2}$ Torr. The structural properties of the samples were analyzed by XRD measurement. The optical properties were investigated by using the photoluminescence spectra obtained with a 325 nm wavelength He-Cd laser. The film surface and carrier concentration were analyzed by an atomic force microscope and Hall measurement system.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.21-26
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• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.57-65
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• 1993

Small XeCl laser of charge transfer discharge excitation was fabricated and output charateristics were investigated according to gas mixture ratio. Beam cross section of 2.7cm${\times}$1.5cm was obtained by constructing excimer laser which preionization is operated automatically and which has chang profile electrode. According to the component gas mixture ratio, the condition of maximum output energy, efficiency were investigated. The maximum energy, efficiency and specific energy were obtained 230 mJ, 1.6% and 1.1 J/l, respectively. The long pulse effect is observed by constructing low peaking to main capacitance ratio of 1:3.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.593-595
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• 1992

To improve the lifetime and output power in a sealed-off $CO_2$ laser, a series of Nd$_{1-x}$Sr$_x$CoO$_3$(x = 0.0, 0.25, 0.40, 0.50, 0.60, 0.75) perovskite-type compounds has been synthesized and used for a cathode material. Using a typical method samples were sintered at 1150$^{\circ}$C and their structures were determined as a cubic form by means of XRD analysis. The degrees of $CO_2$ dissociation were measured by PAS (photoacoustic spectroscopy) with the lapse of time. In the case of $Nd_{0.4}$Sr$_{0.6}$$CoO_3$, which showed the highest catalytic cathode effect, only 7% of the initial $CO_2$ concentration were dissociated at 30 torr of gas mixture and 5 mA of discharge current. The more the gas pressure decreased and the discharge current increased, the more the degree of dissociation occurred. The ability of catalytic cathode to regenerate CO$_2$ in the laser cavity lies in order for x, 0.60 > 0.50 > 0.40 > 0.75 > 0.25 ${\gg}$ 0.0. Except for the case of x = 0.0 the amounts of $CO_2$ dissociation were found to be within 7-15% of the initial $CO_2$ concentration.

• Journal of Sensor Science and Technology
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• v.28 no.1
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• pp.23-29
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• 2019

A copper tetracumylphenoxy phthalocyanine (CuPccp) thin film was formed on an organic insulator film by Langmuir-Blodgett (LB) deposition for gas sensor fabrication. To increase the reproducibility of film transfer, stearyl alcohol was used as a transfer promoter. The structural properties of the CuPccp layers were optically monitored through attenuated total reflection and polarization-modulated ellipsometry techniques. The average thickness of a single layer of the CuPccp LB film was measured to be 2.5 nm. Despite the role of the transfer promoter, the stability of the layer transfer was not sufficient to ensure homogeneity of the LB film. This was probably due to the presence of aggregates in the molecular structure of the CuPccp LB film. Nevertheless, copper phthalocyanine polymorphism can be greatly suppressed by the LB arrangement, which appears to contribute to the improvement of electrical conductivity. The p-type semiconductor characteristics were confirmed by Hall measurements from the CuPccp LB films.

• Journal of Powder Materials
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• v.30 no.1
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• pp.7-12
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• 2023

Metal-additive manufacturing techniques, such as selective laser sintering (SLS), are increasingly utilized for new biomaterials, such as cobalt-chrome (Co-Cr). In this study, Co-Cr gas-atomized powders are used as charge materials for the SLS process. The aim is to understand the consolidation of Co-Cr alloy powder and characterization of samples sintered using SLS under various conditions. The results clearly suggest that besides the matrix phase, the second phase, which is attributed to pores and oxidation particles, is observed in the sintered specimens. The as-built samples exhibit completely different microstructural features compared with the casting or wrought products reported in the literature. The microstructure reveals melt pools, which represent the characteristics of the scanning direction, in particular, or of the SLS conditions, in general. It also exposes extremely fine grain sizes inside the melt pools, resulting in an enhancement in the hardness of the as-built products. Thus, the hardness values of the samples prepared by SLS under all parameter conditions used in this study are evidently higher than those of the casting products.