• Journal of the Korean Society for Precision Engineering
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• v.15 no.8
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• pp.102-108
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• 1998

본 논문에서는 Nd-YAG 레이저 용접 프로세스를 이용하여 두께가 다른 STS304스테인레스 박강판을 대상으로한 점용접에 관한 연구로서, 레이저 용접은 미소부위에 효율적인 접합가공이 가능한 공정으로 비접촉식 가열원을 이용하기 때문에 접합공정 중 기계적 변형이 없고, 레이저 빔을 국부가열원으로 하여 매우 좁은 부분에 제한적으로 열을 가할 수 있어서 강한 금속적 결합이 요구되는 소형부품의 접합에 이용될 수 있다. 뿐만 아니라 공정 변수들을 변화시켜 실제 접합부에 들어 가는 입열량을 쉽게 제어할 수 있다는 등 많은 장점을 가지고 있다. 본 연구에서는 1mm이하의 스테인레스 박판에 대한 레이저 점용접을 FDM과 신경회로망을 이용하여 해석하고 용접부의 너겟 크기, 용접부 깊이 등의 형상을 예측하였다. 또한 레이저 점용접에 있어서의 주요 변수인 펄스 에너지, 펄스 타임, 박판의 두께, 두 판사이의 간극크기 등득 변화시켜 실험하고 수치해석을 검증하기 위하여 여러 가지 강에 대한 레이저 점용접 실험을 수행하였다. 또한 수치해석 시뮬레이션을 위하여 윈도우 프로그래밍을 개발하였다.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.612-619
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• 2002

The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.247.1-247.1
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• 2016

Low-cost, high efficiency solar cells are tremendous interests for the realization of a renewable and clean energy source. ZnTe based solar cells have a possibility of high efficiency with formation of an intermediated energy band structure by impurity doping. In this work, ZnO/ZnTe:Cr and ZnO/i-ZnTe structures were fabricated by pulsed laser deposition (PLD) technique. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnTe target, whose density of laser energy was 10 J/cm2. The base pressure of the chamber was kept at approximately $4{\times}10-7Torr$. ZnTe:Cr and i-ZnTe thin films with thickness of 210 nm were grown on p-Si substrate, respectively, and then ZnO thin films with thickness of 150 nm were grown on ZnTe:Cr layer under oxygen partial pressure of 3 mTorr. Growth temperature of all the films was set to $250^{\circ}C$. For fabricating ZnO/i-ZnTe and ZnO/ZnTe:Cr solar cells, indium metal and Ti/Au grid patterns were deposited on back and front side of the solar cells by using thermal evaporator, respectively. From the fabricated ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cell, dark currents were measured by using Keithley 2600. Solar cell parameters were obtained under Air Mass 1.5 Global solar simulator with an irradiation intensity of 100 mW/cm2, and then the photoelectric conversion efficiency values of ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cells were measured at 1.5 % and 0.3 %, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.197.2-197.2
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• 2015

Low-cost, high efficiency solar cells are tremendous interests for the realization of a renewable and clean energy source. ZnTe based solar cells have a possibility of high efficiency with formation of an intermediated energy band structure by impurity doping. In this work, the ZnTe:O/CdS/ZnO structure was fabricated by pulsed laser deposition (PLD) technique. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnTe target, whose density of laser energy was 4.5 J/cm2. The base pressure of the chamber was kept at a pressure of approximately $4{\times}10-7Torr$. ZnO thin film with thickness of 100 nm was grown on to ITO/glass, and then CdS and ZnTe:O thin film were grown on ZnO thin film. Thickness of CdS and ZnTe:O were 50 nm and 500 nm, respectively. During deposition of ZnTe:O films, O2 gas was introduced from 1 to 20 mTorr. For fabricating ZnTe:O/CdS/ZnO solar cells, Au metal was deposited on the ITO film and ZnTe:O by thermal evaporation method. From the fabricated ZnTe:O/CdS/ZnO solar cell, current-voltage characteristics was measured by using HP 4156-a semiconductor parameter analyzer. Finally, solar cell performance was measured using an Air Mass 1.5 Global (AM 1.5 G) solar simulator with an irradiation intensity of 100 mW cm-2.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.162-168
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• 1999

A new design of four-pass dye laser amplifier affording a narrow-bandwidth pulsed output is demonstrated to suppress the amplified spontaneous emission(ASE) carried by the amplifier output and reduce the possibility of parasitic oscillation in the amplifier. By the direct pulsed amplification of a cw 100 mW dye laser under a Q-switched doubled Nd:YAG laser pumping with energy of 5.6 mJ/pulse, high-peak-power pulsed output with 1.5-mJ energy in 130-MHz bandwidth is obtained corresponding to a power gain greater than $2{\times}10^6$ and an energy efficiency of 27%. The ASE ratio in the four-pass amplifier output is dramatically reduced by using a diffraction grating in the amplifier. Compared with the results obtained from the normal operation of the amplifier with no frequency-selective device, the ASE ratio is reduced by a factor in excess of 10 to remain under 1.5% of the amplifier output whereas the total output energy is slightly increased by ~4%.

• International Journal of Computer Science & Network Security
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• v.24 no.6
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• pp.200-206
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• 2024

Laser induced breakdown spectroscopy (LIBS) technique has been used for the elemental composition of the soils. In this technique, a high energy laser pulse is focused on a sample to produce plasma. From the spectroscopic analysis of such plasma plume, we have determined the different elements present in the soil. This technique is effective and rapid for the qualitative and quantitative analysis of all type of samples. In this work a Q-switched Nd: YAG laser operating with its fundamental mode (1064 nm laser wavelength), 5 nanosecond pulse width, and 10 Hz repetition rate was focused on soil samples using 10 cm quartz lens. The emission spectra of soil consist of Iron (Fe), Calcium (Ca), Titanium (Ti), Silicon (Si), Aluminum (Al), Magnesium (Mg), Manganese (Mn), Potassium (K), Nickel (Ni), Chromium (Cr), Copper (Cu), Mercury (Hg), Barium (Ba), Vanadium (V), Lead (Pb), Nitrogen (N), Scandium (Sc), Hydrogen (H), Strontium (Sr), and Lithium (Li) with different finger-prints of the transition lines. The maximum intensity of the transition lines was observed close to the surface of the sample and it was decreased along the axial direction of the plasma expansion due to the thermalization and the recombination process. We have also determined the plasma parameters such as electron temperature and the electron number density of the plasma using Boltzmann's plot method as well as the Stark broadening of the transition lines respectively. The electron temperature is estimated at 14611 °K, whereas the electron number density i.e. 4.1 × 10¹⁶ cm^-3 lies close to the surface.

• Korean Journal of Materials Research
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• v.15 no.4
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• pp.257-262
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• 2005

Nano-sized ZrVFe alloy powders were prepared by the ablation of powder compact in alcobol using a Nd-YAG pulsed Laser. The $Zr_{57}V_{35.}8Fe_{7.2}$ alloy commercially designated as ST707 has long been known as the ideal solution for various vacuum applications. The target for the ablation was sintered pellets of $Zr_{57}V_{35.}8Fe_{7.2}$ alloy powder. The alloy was prepared by arc melting and Hydride-DeHydride method. The ablated powders were mostly circular having fairly large size distribution smaller than 200 nm in all cases. The X-ray diffraction study revealed that the ablated alloy retained the crystal structure of the target alloy. Nevertheless, Fe and V contents in the ablated powder were lower than those in the target alloy. This was believed to result from the high vapour pressures of Fe and V compared to that of Zr. The size of the powders ablated at high energy fluence tends to decrease due at least partly to the breakdown of previously made ones.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.306.1-306.1
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• 2016

ZnO semiconductor material has been widely utilized in various applications in semiconductor device technology owing to its unique electrical and optical features. It is a promising as solar cell material, because of its low cost, n-type conductivity and wide direct band gap. In this work ZnO/Si heterojunctions were fabricated by using pulsed laser deposition. Vacuum chamber was evacuated to a base pressure of approximately $2{\times}10^{-6}Torr$. ZnO thin films were grown on p-Si (100) substrate at oxygen partial pressure from 5mTorr to 40mTorr. Growth temperature of ZnO thin films was set to 773K. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnO target, whose density of laser energy was $10J/cm^2$. Thickness of all the thin films of ZnO was about 300nm. The optical property was characterized by photoluminescence and crystallinity of ZnO was analyzed by X-ray diffraction. For fabrication ZnO/Si heterojunction diodes, indium metal and Al grid patterns were deposited on back and front side of the solar cells by using thermal evaporator, respectively. Finally, current-voltage characteristics of the ZnO/Si structure were studied by using Keithly 2600. Under Air Mass 1.5 Global solar simulator with an irradiation intensity of $100mW/cm^2$, the electrical properties of ZnO/Si heterojunction photovoltaic devices were analyzed.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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• pp.43-58
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• 1998

The Kwinana Shoreline Fumigation Experiment (KSFE) took place at Fremantle, WA, Australia between January 23 and February 8, 1995. The CSIRO DAR LIDAR measured plume sections from near the Kwinana Power Station (KPS) stacks to up to about 5 km downstream. It also measured boundary layer aerosols and the structure of the boundary layer on some occasions. Both stages A and C of KPS were used as tracers at different times. The heart of the LIDAR system is a Neodymium-doped Yttrium-aluminum-garnet (Nd:YAG) laser operating at a fundamental wavelength of 1064 nm, with harmonics of 532 nm and 355 nm. For these experiments the third harmonic was used because the UV wavelength at 355 nm is eye safe beyond about 50 m. The laser fires a pulse of light 6 ns in duration (about 1.8 m long) and with an energy (at the third harmonic) of about 70 mJ. This pulse subsequently scattered and absorbed by both air molecules and particles in the atmosphere. A small fraction of the laser beam is scattered back to the LIDAR, collected by a telescope and detected by a photo-multiplier tube. The intensity of the signal as a function of time is a measure of the particle concentration as a function of distance along the line of the laser shot. The smoke plume was clearly identifiable in the scans both before and after fumigation in the thermal internal boundary layer (TIBL). Both power station plumes were detected. Over the 9 days of operation, 1,568 plumes scans (214 series) were performed. Essentially all of these will provide instantaneous plume heights and widths, and there are many periods of continuous operation over several hours when it should be possible to compile hourly average plume statistics as well. The results of four days LIDAR observations of the dispersion of smoke plume in the TIBL at a coastal site are presented for the case of stages A and C.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.24-24
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• 2015

최근 생체재료의 개발이 눈부시게 발전되고 생체적합성이 우수한 표면을 요구함에 따라 생체재료의 표면처리에 대한 연구가 활발히 진행되고 있다. Laser Deposition법은 항공기 부품제조 분야에 주로 사용되고 있으며 최근에 오하이오 주립대 타이타늄합금연구센터를 중심으로 표면처리에 관한 연구가 주로 이루어졌다. 특히 이를 이용하여 치과재료의 표면처리에 응용을 시도하였다. 치과에서 응용될 수 있는 경우는 주로 임플란트는 부분 또는 완전 무치악 환자의 보철수복에 사용되는 보철물의 제작등에 사용될 수 있으며 이중에서도 특히 생체용 임플란트의 표면처리응용으로 임플란트와 조직간의 접합성을 개선하는 표면처리법으로 연구되었다. 임플란트의 성공과 실패는 물성적인 측면에서 임플란트의 형태, 표면거칠기 및 표면처리방법, 초기하중 등에 의하여 좌우되며 임플란트 재료에 작용하는 응력차폐는 생체적합성을 좌우하는 큰 요인이 되고 있다. 이를 위하여 저 탄성계수합금을 설계하지만 하중을 버티는 강도가 낮아지는 단점이 있어 레이저증착법을 이용하여 임플란트재료인 Ti6Al4V합금에 탄성계수가 낮은 Ta, Nb등을 코팅하는 방법을 통하여 이를 해결하고자하는 시도가 이루어지고 있다. 이 방법은 최근의 3D 프린팅의 원리가 되고 있다. 따라서 발표에서는 Laser Deposition방법을 이용하여 치의학분야에서 응용되고 있는 예를 강연하고 응용 가능 분야에 대하여 토론 하고자한다. 또한 펨토레이저를 이용하여 생체합금의 표면처리는 생체활성화를 더욱 증진시키며 이를 위하여 많은 연구 수행되고 있다. 본 발표에서는 매식용 합금 표면에 펨토레이저를 이용하여 텍스춰링하여 세포가 잘 성장 할 수 있는 크기의 조절함으로써 기존의 표면처리와는 다른 효과를 얻을 수 있는 장점을 알아본다. 펨토레이저를 이용하면 여러 가지 형태의 텍스춰링이 가능하며 원형, 사각형등등 자유자제로 형태의 묘사가 가능하고 깊이 또한 쉽게 조절할 수 있는 장점이 있다. 지금까지는 표면 개질에 사용되는 레이저는 주로 Nd:YAG 레이저의 파장을 반으로 줄인 녹색레이저 (${\lambda}=532nm$)를 사용하거나, 자외선파장영역의 레이저를 사용하는 경우가 일반적으로 가장 보편화되었다. 이를 이용하여 제조된 Ti합금에 펨토 초(10-15 second) 펄스폭 대역을 갖는 레이저를 이용하여 나노크기의 미세 요철을 표면에 형성한 후, 나노튜브를 형성하여 그 표면특성의 변화를 알아보고 펨토레이저가 의료분야에 적용되고 있는 예를 살펴보고자 한다.