• 한국통신학회논문지
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• 제18권12호
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• pp.1935-1944
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• 1993

레이저 다이오드단면의 최적 무반사 코팅 조건을 활성층 두께의 함수로써 세가지 간단한 수치해석 방법을 사용하여 계산하였다. 세가지 간단한 수치해석 방법을 사용하여 얻은 결과가 서로 가른 것은 각 방법에서 사용한 레이저 다이오드내의 유효 굴절율이 다르기 때문이다. 또한 간단한 수치해석 방법의 정확성을 검토하기위하여 정확한 수치해석 결과와 그 결과들을 비교하였다. 레이저 다이오드의 유효 굴절율이 도과모드를 구성하는 각 편면파의 입사간도에 따라 변해 굴절율이 도파모드를 구성하는 각 평면파의 입사각도 따라 변화하도록 설정한 방법이 TE와 TM 모드에 대해서 또 활성층 굴절율과 클래딩층의 굴절율차가 작은 경우 클 경우 각각에 대하여 정확한 수치해석 결과와 잘 일치함을 알 수 있었다.

• 한국정밀공학회지
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• 제18권10호
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• pp.134-147
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• 2001

Laser cladding process accompanies phase transformations from melting (on heating) through solidifying (on cooling) at the same time within a small material volume and to final solid phase. The phase transformations are not reversible, but an irreversible thermodynamic process; they accompany either absorption or release of thermal energy (referred to latent heat) during transformation. Yet, most analyses on materials processed by laser as a heat source have been performed on models of neglecting the latent heat in the process and those did not Justify the simplification. With literatures on the laser material process, we have not place an answer to how little the assumption affects on analyses. This led us to our current study: the effects of latent heat on thermo-mechanical analysis. To this end, we developed a fairly accurate program accommodating an algorithm for enforcing the latent heat whenever necessary and ran it combining with ABAQUS$^{TM}$. The simulation techniques we used in this study were verified by directly comparing our prediction with experimental publications elsewhere; our numerical results agreed accurately with the experiments. On the effects of the latent heat, we performed two alternatives about considering the latent heat in analysis, and compared each other. As a result, we found that more accurate conclusions might come out when considering the latent heat in process analyses.s.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.56-60
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• 2008

Laser cladding technology was studied as a method for upgrading the present repair procedures of damaged tubes in a nuclear steam generator and Doosan subsequently developed and designed a new Laser Cladding Repair System. One of the important features of this newly developed Laser Cladding Repair System is that molten metal can be deposited on damaged tube surfaces using a laser beam and filler wire without the need to install sleeves inside the tube. Laser cladding qualification tests on the steam generator tube material, Alloy 600, were performed according to ASME Section IX. Residual stress analyses were performed for weld metal and heat affected zone of as-welded and PWHT with SYSWELD software.

• Journal of Welding and Joining
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• 제25권4호
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• pp.49-57
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• 2007

The optimization of the cladding parameters was studied to maximize the deposition efficiency in the laser cladding using a low power pulsed Nd:YAG laser. STS304 stainless steel plate and Co alloy powder were used as a substrate and powder for cladding, respectively. The six cladding parameters were selected through preliminary experiments and their effects on the deposition efficiency were analyzed statistically. Experiments were designed and carried out using the Taguchi experimental method using a L18 orthogonal array. It was found from the results of analysis of variance(ANOVA) that the powder feed position and powder feed angle had the most significant effects on the deposition efficiency, but the powder feed rate and laser focal position had nearly no effects. The deposition efficiency could be maximized at 0mm of the powder feed position and 50o of the powder feed angle in the experimental range. From this experimental analysis, a new laser cladding head with 20o of the powder feed angle was designed and manufactured. With a new laser cladding head, the highest deposition efficiency of 12.2% could be obtained.

• 전자공학회논문지D
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• 제36D권5호
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• pp.88-98
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• 1999

레이저의 종축방향으로 회절격자층을 형성하는 위쪽 클래딩 층의 가운데 부분의 굴절률을 양 옆부분과 다르게 하여 유효위상천이 효과를 넓은 영역에서 얻는 refractive index midulated (RIM) DFB 레이저를 제안한다.RIM-DFB 레이저는 SHB 효과를 줄이기 위하여 기존에 제안되었던 회절격자의 주기를 변화시켜 넓은 영역에 걸쳐서 유효 위상 천이를 주는 corrugation pitch modualtion (CPM) 방법과 레이저의 종축 방향으로 결합계수를 달리하여 주는 distributed coupling coefficients (DCC) 방법의 효과를 동시에 얻을 수 있는 실현 가능한 구조이다. 급격한 위상천이가 없기 때문에 광자밀도분포가 균일해져 SHB 효과가 줄어 들게 되며 레이저 공진기 가운데 부분의 결합계수가 양 옆 부분의 결합계수보다 커서 분포결합계수의 효과를 주기 때문에λ/4 위상천이 레이저와 CPM-DFB 레이저에 비해 고출력에서 좋은 단일 모드 특성을 보인다. 그리고, 굴절률이 다른 가운데 부분의 길이가 RIM-DFB 레이저의 동작특성에 미치는 영향에 대하여 연구하였다.

• 한국광학회지
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• 제32권3호
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• pp.120-125
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• 2021

본 연구에서는 다파장 빔결합을 위한 master oscillator power amplifier (MOPA) 구조의 선편광 고출력 이터븀 첨가 광섬유 레이저를 개발하였다. 유도 브릴루앙 산란(stimulated Brillouin scattering, SBS)을 억제하기 위하여 pseudo-random binary sequence (PRBS) 신호로 위상 변조 및 비트길이를 최적화한 선폭 약 10 GHz의 시드 레이저를 구현하였으며, 이를 이용하여 3단 증폭을 하였다. 주 증폭단에서는 모드 불안정성 현상(mode instability, MI)의 문턱값을 높이기 위하여 코어 및 클래딩의 직경이 각각 20 ㎛, 40 ㎛인 편광유지(polarization maintaining, PM) 이터븀 첨가 광섬유를 이용하고 지름이 약 9-12 cm인 나선형 홈에 적용하였다. 그 결과, 입사된 여기광 대비 기울기 효율이 83.7%인 1.004 kW의 레이저 출력을 얻었다. 또한, 빔품질(M²)과 편광소광율(polarization extinction ratio, PER)은 각각 1.12와 21.5 dB로 측정되었다. 더욱이, 역방향 스펙트럼의 레일리 신호와 SBS 신호의 첨두 세기 비율은 2.36 dB로 관측되어, SBS가 완화된 레이저 구현을 확인하였다. 또한 증폭 출력에 따라 기울기 효율 및 빔품질의 저하가 없어 모드불안정이 발생하지 않음을 확인하였다.

• 마이크로전자및패키징학회지
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• 제24권3호
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• pp.53-56
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• 2017

Laser cladding is a technique for forming beads by melt-sintering with a laser while directly feeding metal powder onto the base material through nozzles. This technique, which is applied in laser surface treatment technology, is useful for repairing broken or worn parts by allowing selective formation of the surface layer of the base metal material. In this paper, laser cladding process was performed on STS316L powder using high power continuous wave laser with IR wavelength and the cladding characteristics according to process conditions were experimentally analyzed.

• Journal of Welding and Joining
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• 제19권5호
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• pp.481-485
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• 2001

Laser cladding processing allows rapid transfer of heat to the material being processed with minimum conduction into base metal. The effect of $CO_2$ laser cladding with high viscosity mixed powders was investigated. High viscosity mixed powder consists of bronze powder and flux that is used at a high temperature condition. The mixed powder has a high viscosity that it can be easily pasted over a curved or slope substrate. The device for mixed powder was designed and manufactured. It consists of the high viscosity mixed powder feeding system, the preheating system and the shielding gas system which prevents the clad layer from being oxidized. The results of experiment indicated that the feed rate of high viscosity mixed powder was important for later cladding with mixed powder feeding. The high viscosity mixed powder and substrate must be preheated to prevent porosity from breaking at the clad layer. The experimental result shows that the high viscosity mixed can be applied for laser cladding process.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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• pp.256-259
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• 2000

High viscosity mixing powder is a very useful material for laser cladding. This material has a high viscosity so that it can be sticked to substrate. Therefore, Laser cladding can be performed on a curved or slope surface. Laser cladding can be easily performed with the material instead of wire that is difficult to be manufactured in some case. In this experiment, it was used a high viscosity mixing powder which consists of a high temperature flux and a bronze powder. And AC2B alloy material was used as a substrate. Flux prevents the clad layer from being oxidized and increases bonding property between substrate and cladding material. It makes possible to laser cladding at low level energy.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.196-198
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• 2007

Laser cladding technology was studied as a method for upgrading the present repair procedures of damaged tubes in a nuclear steam generator and Doosan subsequently developed and designed a new Laser Cladding Repair System. One of the important features of this newly developed Laser Cladding Repair System is that molten metal can be deposited on damaged tube surfaces using a laser beam and filler wire without the need to install sleeves inside the tube. Laser cladding qualification tests on the steam generator tube material, Alloy 600, were performed according to ASME Section IX.