• 한국광학회지
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• 제31권3호
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• pp.142-147
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• 2020

본 연구에서는 Yb 광섬유 레이저 MOPA (master oscillator power amplifier) 시스템을 구축하여 고출력, 고효율의 근적외선 레이저 빔을 발진시키고, 이를 주기분극반전 준위상정합 비선형 광학 소자인 MgO:PPSLT에 단일 통과시키는 방식을 통하여 고출력 고효율 연속발진 녹색 레이저 빔을 생성하는 방법을 보고한다. 자발 펄싱을 억제할 수 있는 패브리-패롯 피드백 공진기 구조를 사용한 광섬유 레이저 주공진기를 사용하여 선폭이 좁고 선형 편광된 1064 nm 레이저 씨앗 빔을 안정적으로 생성할 수 있었으며, 이를 Yb 광섬유 증폭단에서 고출력으로 증폭시켰다. 증폭된 레이저 빔을 MgO:PPSLT에 통과시켜 고출력 고효율의 이차조화파를 얻을 수 있었는데, 이때 얻은 532 nm 레이저의 최고 출력은 기본 입사광의 출력이 25.0 W일 때 11.1 W였으며, 변환 효율은 44.4%를 얻었다.

• 한국광학회지
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• 제20권6호
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• pp.339-345
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• 2009

결정을 이용하여 고출력 단일모드 특성을 가지는 수직공진 표면발광 레이저를 제작하고 발진 특성을 관찰하였다. 일반적으로 광 밴드갭 형성을 위해 수십개의 광 결정 홀을 식각하나, 이번 연구에서는 6개의 홀만으로 단일모드를 구현하였고, 폴리이미드로 홀을 메우게 되어 신뢰성이 유리한 장점이 있다. 산화 구경과 광 결정 홀의 크기를 변화시키며 실험을 진행하여 단일모드 특성의 변화를 분석하였다. 다양한 광 결정 구조를 가진 수직공진 표면발광 레이저에서 고출력 단일모드 발진이 가능함을 확인하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.561-569
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• 2002

Laser has been called a "Quantum Machine" because of its mechanism of generation since the development on July 7,1960.by T.H.Maiman. We can now use this machine as a tool for manufacturing in industries. At present, 45kW CO2 laser, 10kW Nd:YAG laser, 6kW LD pumped YAG laser and 4kW direct diode laser facilities are available for welding a heavy steel plate of 40mm in thickness and for cutting metals at high speed of 140m/min. Laser Materials Processing is no longer a scientific curiosity but a modern tool in industries. Lasers in manufacturing sector are currently used in welding, cutting, drilling, cladding, marking, cleaning, micro-machining and forming. Recently, high power laser diode, 10kW LD pumped YAG laser, 700W fiber laser and excimer laser have been developed in the industrialized countries. As a result of large numbers of research and developments, the modem laser materials processing has been realized and used in all kinds of industries now. In the present paper, metallurgical studies on laser materials processing such as porosity formation, hot cracking and the joint performances of steels and aluminum alloys and dissimilar joint are discussed after the introduction of laser facilities and laser applications in industries such as automotive industry, electronics industry, and steel making industry. The wave towards the use of laser materials processing and its penetration into many industries has started in many countries now. Especially, development of high power/quality diode laser will be accelerate the introduction of this magnificent tool, because of the high efficiency of about 50%, long life time and compact.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.118-119
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• 2013

High power, short wavelength red laser diodes (LDs) have attracted significant interests in a variety of fields due to their advantages in terms of reliability, compactness and cost. The higher brightness for human eyes is required, the shorter wavelength like 630 nm is necessary with higher output power. In this respect, LDs are promising as alternative candidates of gas or dye lasers for such applications due to their small size, high optical/electrical power conversion efficiency, robustness and so on. The crystalline quality of GaInP-AlGaInP multiple quantum wells (MQWs) and AlInP cladding layers is a crucial part in the device performance of GaInP red LDs. Here, we first investigated the effect of Si diffusion on the optical properties of GaInP-AlGaInP MQWs grown with different growth temperatures. Secondary ion mass spectroscopy (SIMS) measurements revealed that both the Mg and Si diffusion into MQW active region was significant. To reduce such diffusion, we employed undoped Mg and Si diffusion barrier and could improve the properties.Without both Mg and Si diffusion barriers, no lasing emission was observed. However, lasing emission was observed clearly for the red LDs with both Mg and Si diffusion barriers. We then investigated the temperature dependent optical properties of MQW layers grown with different well thicknesses (6, 8 and 10 nm). When the well thickness was 10 nm, the better crystalline quality was obtained. However, the observed LD performances were similar, probably due to the defects and impurities in the AlGaInP layer. Further investigation with the detailed analyses will be presented later.

• 한국레이저가공학회지
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• 제11권4호
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• pp.7-12
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• 2008

Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• 한국광학회지
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• 제13권4호
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• pp.347-355
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• 2002

티타늄 사파이어 레이저에 대한 활용도를 높기 위하여 4개의 거울로 구성된 Z-형태의 대칭형 레이저 공진기를 구성하여 넓은 파장가변성을 갖는 고효율 연속 발진 티타늄 사파이어 레이저를 제작하였다. 또한 Kerr-렌즈 모드-록킹(KLM)을 일으키기 위한 KLM 강도 및 공진기 모드 크기가 Kerr 매질을 포함하는 Z-형태의 대칭형 공진기에 대하여 공진기 내의 위치, 내부 공진기 레이저 출력 및 안정 파라메터 등에 의존함을 확인하였고, 이를 근거로 하여 펌핑 효율이 높고 KLM 강도가 강한 KLM 티타늄 사파이어 레이저를 제작하여 출력 특성, 펄스폭 및 스펙트럼 반치폭 등을 측정하였다. 그 결과 연속 발진 티타늄 사파이어 레이저의 출력에 대한 기울기 효율은 31.3%이고, 5W의 Ar-이온 펌핑 레이저 출력에 대해 최대 1420㎽의 평균 출력을 얻을 수 있었으며, 파장가변 영역은 730㎚~908㎚까지 모두 700㎽ 이상의 평균 출력을 보였다. 자체-조리개 효과에 의한 KLM 동작 또한 쉽게 얻을 수 있었으며, KLM된 티타늄 사파이어 레이저로부터 출력에 대한 기울기 효율은 16%이고, 5W 펌핑 출력에 대해 최대 500㎽의 평균 출력을 얻었다. 또한 중심 파장 807㎚에서 스펙트럼 반치폭이 33㎚이며, 펄스 반복률이 82㎒인 27fs의 안정된 짧은 펄스를 얻을 수 있었다.

• Journal of Welding and Joining
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• 제20권2호
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• pp.95-101
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• 2002

After high power lasers are avaliable in the commercial market, the number of applications of the laser welding has been increased in manufacturing industries. Although the tailored blank laser welding of butt jointed steel sheets is well known recently in the automotive industries, the lap joint laser welding is a new technology to the automotive manufacturing people as well as the design people. But the deep penetration laser welding seems to be preferred to the partial penetration welding for the lap joint welding in the automotive manufacturers because the partial penetration is a serious deflect for the butt joint. In this study, the feasibility of partial penetration welding fur the lap joint $CO_2$ laser welding was studied fur the 1mm thick 390MPa high strength steel sheets for automotive bodies. The process window of the lap joint partial penetration welding was obtained from experiments with the gap size and the welding speed as process parameters. The partial penetration welding was found excellent on the basis of the tensile shear strength and sectional geometry. The bead width, input energy Per volume, tensile-shear strength, deformation energy and the sectional geometries after tensile-shear tests of partial penetration welded specimens are compared with those of full penetration welded specimens with a series of gaps and welding speeds.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1780-1781
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• 2011

There have been numerous studies on application of robots to in-pipe inspection system. In this thesis, a mobile robot that can move through elbows and vertical pipes having diameter 100mm is developed. Defect detection technology for locating wall-thinnings, corrosions and foreign materials is developed for high temperature and pressure pipings in thermal power plants, utilizing laser sensors installed on the robot. Actual defect detection performance is evaluated with application of the developed robot system to a mock-up pipings.

• Current Optics and Photonics
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• 제7권1호
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• pp.90-96
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• 2023

We numerically solve the nonlinear Schrödinger equation for pulse propagation in a passively mode-locked Yb:KGW laser. The soliton-like pulse formation as a result of balanced negative group-delay dispersion (GDD) and nonlinear self-phase modulation is analyzed. The cavity design and optical parameters of a previously reported high-power Yb:KGW laser were adopted to compare the simulation results with experimental results. The pulse duration and energy obtained by varying the small-signal gain or GDD reproduce the overall tendency observed in the experiments, demonstrating the reliability and accuracy of the model simulation and the optical parameters.

• 한국태양에너지학회 논문집
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• 제39권3호
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• pp.9-17
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• 2019

Laser cutting cell of solar cells can achieve high voltage and efficiency through more array than conventional 6 inch cell compared to same area. In this study, we fabricated c-Si cutting cell with various lasers and laser conditions such as power, speed, and number of times. In the case of picosecond laser, excellent surface characteristics were obtained due to small surface defects and low thermal damage at the output of 20W and the speed of 100 mm/s. However, it is not possible to fabricate a cutting cell having good characteristics due to nonuniform cutting inside the wafer when the processing for forming a cutting cell is not sufficiently performed. For nanosecond lasers, the best wafer characteristics were obtained for fabrication of excellent cutting cells at a frequency of 500 kHz and a laser speed of 100 mm/s. However, the nanosecond laser has not been processed sufficiently in the condition of a number of times. As a result, it was confirmed that the wafer thickness was cut by $63{\mu}m$ of the cell thickness of $170{\mu}m$ in the condition of five times of laser process. It was found that more than 30% of the wafer thickness had to be processed to fabricate the cutting cell. After cutting the 6-inch cell having the voltage of 0.65 V, we obtained the voltage of about 0.63 V.