• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.44-55
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• 2003

The Nd:YAG laser process is known to have high speed and deep penetration capability to become one of the most advanced welding technologies. This paper describes the machining characteristics of SM45C carbon steel welding by use of an Nd:YAG laser. In spite of its good mechanical characteristics, SM45C carbon steel has a high carbon contents and suffers a limitation in the industrial application due to the poor welding properties. The major process parameters studied in the present laser welding experiment were position of focus, travel speed and laser power. Optical microscope and SEM were used to investigate the microstructures of the welded zone. The experimental results showed that penetration depth of the welding process increases with laser power. Both the microstructural investigation and the theoretical calculations indicated that materials undergoes a very high heating and cooling cycle during welding process. It was also found that the austenite nucleation takes place at the initial stage and the completion temperature of austenite transformation is much higher than in the case of the arc welding.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.829-837
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• 1993

Chemically and geometrically homogeneous mixing of Si3N4 powders with sintering additives(YAG, 3Y2O3$.$5Al2O3) was attempted via coprecipitation method. X-ray dot maps for the additive elements(Al and Y) showed that the additives are evenly distributed in the powder mixture prepared by coprecipitation method(CP). TEM observation of the coprecipittion-treated Si3N4 powders revealed that they are covered with extremely fine crystallites of additive. The shift in isoelectric point(IEP) of Si3N4 powders from pH 6.7 to pH 7.9 after coprecipitation mixing gave another evidence for coating of Si3N4 powders with YAG additives. SIMS analysis for composition on the surface and in the matrix of mixed powders showed that the YAG additives are highly enriched on the surface of coprecipitation-treated Si3N4 powders. Especially when a small amount of additive was used, the effect of homogeneous additive distribution on densification was preceptible: After pressureless-sintering of powder compacts containing 5 mol% YAG at 1800$^{\circ}C$ for 0.5h, a sintered density of 96.5% theoretical was obtained from the specimens prepared bycoprecipitation in comparison with 93.8% from the mechanically-mixed one.

• Journal of Periodontal and Implant Science
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• v.44 no.5
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• pp.227-234
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• 2014

Purpose: Dentin hypersensitivity is a potential threat to oral health. Laser irradiation may provide reliable and reproducible treatment but remains controversial. The present study aimed to evaluate the effects of $CO_2$ or erbium-doped yttrium aluminium garnet (Er:YAG) laser therapy, and to assess mineral content. Methods: Eighteen human single-rooted teeth affected with advanced periodontitis were obtained. Buccal and lingual surfaces were planed to form 36 specimens. Ethylenediaminetetraacetic acid gel (24%) was applied to remove the smear layer and simulate hypersensitive teeth. The experimental groups were: group 1, control (no irradiation); group 2, $CO_2$ laser (repetitive pulsed mode, 2 W, $2.7J/cm^2$); and group 3, Er:YAG laser (slight contact mode, 40 mJ/pulse and 10 Hz). To evaluate dentinal tubule occlusion, six specimens per group (2-mm thickness) were prepared and observed using scanning electron microscopy (SEM) for calculation of the occlusion percentage. To evaluate the mineral content, six specimens per group (0.6-mm thickness) were used, and then the levels of Ca, K, Mg, Na, and P were measured by inductively coupled plasma-atomic emission spectrometry. In addition, the surface temperature of the specimens during laser irradiation was analyzed by a thermograph. Results: The SEM photomicrographs indicated melted areas around exposed dentinal tubules and a significantly greater percentage of tubular occlusion in the $CO_2$ and Er:YAG laser groups than the control, and in the Er:YAG group than the $CO_2$ laser group. In addition, no significant differences were noted among the experimental groups for the mineral elements analyzed. The $CO_2$ laser group showed an evident thermal effect compared to the Er:YAG group. Conclusions: $CO_2$ and Er:YAG laser are effective in treating dentin hypersensitivity and reducing its symptoms. However, the Er:YAG laser has a more significant effect; thus, it may constitute a useful conditioning item. Furthermore, neither $CO_2$ nor Er:YAG lasers affected the compositional structure of the mineral content.

• Journal of Periodontal and Implant Science
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• v.26 no.1
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• pp.276-292
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• 1996

The purpose of this study was to evaluate whether removal of gingival epithelium with pulsed Nd :YAG laser could inhibit the downgrowth of junctional epithelium after alloplastic material grafting in periodontal bone defect. The periodontal bone defects were created surgically on the palatal aspect of the upper right and left molar teeth in 30 rats and filled with resorbable calcium carbonate($Biocoral\;450^{(R)}$: Inoteb, France). The control sites(right molar area) was sutured. The test side (left molar area) received controlled deepithelization of the oral and sulcular epithelium with pulsed Nd:YAG laser($Sunrise\;Maste^{(R)}$: Sunrise Technologies, U.S.A.) under the mode of 1.75W, 15Hz, 116mJ/pulse and was sutured. The control and test sites were evaluated clinically and histologically, at 1, 3, 7, 14, and 28 days postoperation. Clinically, the gingiva showed normal color and shape at the 5th day in the control site and at the 10th day in the test sites. Histologically, the junctional epithelium was formed at the 7th day in the control sites and at the 14th day in the test sites, and the long JE attachment were observed at the 28th day in both sites. The attachment of connective tissue to root surface was observed initially at the 7th day in the control sites and at the 14th day in the test sites, and completed at the 28th day in both sites. In summary, these results showed that the removal of oral epithelium using pulsed Nd:YAG Laser could not prevent epithelial downgrowth after alloplastic material implantation in rat periodontal bone defect.

• Korean Journal of Crystallography
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• v.11 no.3
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• pp.151-156
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• 2000

Yb/YAG single crystals were grown from the melt composition of Y/sub 1-x/Yb/sub x/)₃Al/sub 5/O/sub 12/ where x equal to 5, 10, 15, 20, 25, 33, 50, 75 and 100 at % by floating zone method. Optimum growth parameters to get high quality single crystals were 3.5 mm/h of growth rate and 20 rpm of rotation rate under the N₂ atmosphere. After the growth, color of crystals was appeared with pale blue due to the lack of oxygen, but it was disappeared after annealing at 1450℃ for 2 hr. Absorption coefficients were linearly increased depending on the concentration of Yb/sup 3+/ ions. Broad emission band was measured in the range of 1020 to 1050 nm with the peak intensity at 1031 nm and 1051 nm because of ²F/sub 5/2/(1)→²F/sub 7/2/(3) and ²F/sub 5/2/(1)→²F/sub 7/2/(4) transition respectively. When Yb/sup 3+/ ions were substituted with high rates, there were tendency to decrease the measured fluorescent lifetime for Yb ions depending on the concentration of Yb/sup 3+/ ions.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.961-966
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• 1995

국내 상업적으로 운용증인 경수로 원자력 발전소중, 중기발생기의 건전성 유지를 위하여 보수 유지에 많은 비용을 소비하고 있다 특히 중기발생기 전열관으로 사용되는 inconel 600 재질에 많은 문제점이 발생되었다. 전열관 파손에 대한 보수 및 방지기술은 plugging, sleeving, shot penning, Ni-plating 등이 있다. 특히 최근에 개발된 고출력 Nd:YAG 레이저를 이용한 sleeving 보수 기술이 개발되었다. Nd:YAG 레이저를 이용한 보수 방식은 미국의 WH 및 일본의 MHI 등이 선정하여 실용화 단계에 있으며, 이는 광섬유로 전송이 가능한 Nd:YAG 레이저를 이용하여 원격으로 가공할 수 있는 기술이다. 현재 한국 원자력 연구소에서는 전열관 레이저 보수 용접에 대한 개념을 확립하고 장비 및 기구를 개발하였으며, 고리 1 호기 전열관규격에(7/8") 3/4" sleeve tube를 삽입하여 약 50 m 떨어진 곳으로부터 원격 레이저 용접을 실험실적 규모로 실증 하였다.모로 실증 하였다.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.434-440
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• 2000

We fabricated a high power Nd:YAG laser pumped by a 1 kW diode laser with a Lambertian-type diffusive reflector. Maximum cw power of 500 W with a slope efficiency of 49%, which corresponds to an optical efficiency of 46.7%, was obtained from a short linear resonator when a 5 mm rod was used. The efficiencies decreased when a 6 mm rod was used, due to the poor quality of the absorption distribution in the rod. The measured beam quality factor of 70, which is slightly smaller than the value calculated from the measured thermal focal lengths, shows that the absorption distribution in the rod is fairly uniform. iform.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.19-26
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• 2005

The objective of this study is to investigate the influence of process parameters, such as power of laser, cutting speed of laser and material thickness, on the practical cutting region and the kerfwidth fer the case of cutting of CSP IN sheet using high power Nd:YAC laser in continuous wave(CW) mode. In order to obtain the practical cutting region and the relationship between process parameters on the kerfwidth, several laser cutting experiments are carried out. The effective heat input is introduced to consider the influence of power and cutting speed of laser on the kerfwidth together. From the results of experiments, the allowable cutting region and the relationship between the effective heat input and kerfwidth fur the case of cutting of CSP 1N sheet using high power CW Nd:YAG laser have been obtained to improve the dimensionalaccuracyofthecutarea.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.1
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• pp.1-7
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• 2016

RE : YAG ($RE=Nd^{3+}$, $Er^{3+}$) single crystals are laser diodes and generally grown by Czochralski method with controlling the various growth parameter. Since the defects occurred by temperature gradient or the rotation speed of solid-liquid growth interface act as the decline of crystal optical property during the growth procedure, crystalline quality improvement via defects analysis is necessary. The etch pit density (EPD) analysis was used to confirm the surface defect of grown RE : YAG single crystal and to select the area of transmission electron microscopy (TEM) analysis. Defects in the specimen produced by tripod polishing method such as buckling, rod shaped, bend contours by internal stress, segregation and others were observed by using 200 kV TEM and 300 kV FE-TEM.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.22 no.1
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• pp.33-42
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• 2000

The purpose of this study was to compare the wound healing process after skin incision using scalpel, $CO_2$ laser and pulsed Nd:YAG laser in rats. After skin on the back was incised 3 cm long, rats were sacrificed at 1, 3, 7, 14, 21 and 28 days. Macroscopic, histologic and immunohistochemical examinations using the collagen type IV and the CD34 antibodies which are necessary to the forming process of new capillary were performed. Results obtained were as follows ; Macroscopically the initial wound healing of the laser group was about $1{\sim}2$ weeks slower than that of the scalpel group. There weren't however any remarkable differences in all groups in 4 weeks after incision. By histologic finding, acute inflammatory cells were more prominent during the initial wound healing in the scalpel group than in the other groups. Epithelialization started in the order of scalpel, $CO_2$ and Nd:YAG laser group after skin incision. By the Masson's trichrome stain, collagen synthesis in the Nd:YAG laser group was more slowly initiated than in the other groups. But it was completed at the $3{\sim}4$ weeks in all groups. Immunohistochemically, collagen type IV and CD34 expression were markedly increased at 2 weeks in the scalpel and $CO_2$ laser group. Meanwhile, in the Nd:YAG laser group, these reactions were observed later tan the other groups. Collagen type IV and CD34 expression were decreased in all groups after 4 weeks. These results suggest that $CO_2$ and Nd:YAG laser showed similar healing process compared with scalpel and a potential substitute for scalpel in skin incision.