• Title, Summary, Keyword: Pulsed Laser

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Heat Transfer Analysis of the Opaque Solid Heated by Pulsed Laser (Pulsed Laser에 의하여 가열되는 불투명 고체의 열전달 해석)

  • 전민호;이은호;유재석
    • Journal of Energy Engineering
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    • v.8 no.1
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    • pp.181-188
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    • 1999
  • 재료의 표면을 pulsed laser로 가열할 때, 유한한 두께를 가지는 반무한 평판의 온도분포를 해석하여 열확산계수, 재료의 두께, 열원의 주기, 그리고 열원의 반경이 온도분포에 미치는 영향을 알아보았다. Pulsed laser에 의하여 가열되는 불투명 고체의 시간에 따른 온도는 전체적으로 증가하지만 열원의 주기와 동일한 주기를 가지고 일정한 온도차를 가지는 전체온도와 평균온도의 차, Tac가 존재한다. 열확산계수가 증가하면 재료 내부로 에너지의 확산이 활발하기 때문에 Tac는 커진다. 재료의 두께가 열확산길이보다 얇은 경우에는 두께변화에 따라서 온도가 민감하게 변하지만, 열확산길이보다 재료의 두께가 두꺼울 때는 두께의 변화에 관계없이 거의 일정한 온도가 나타난다. 열원의 단속주파수가 증가하면 한 주기당 에너지가 작아지므로 Tac의 크기는 작아진다. 열원의 반경이 커지면 단위면적당 에너지가 감소하므로 Tac의 크기는 삼각파, 싸인파, 사각파 순으로 크게 나타난다. 따라서 열원의 파형을 측정하여 이를 적용하는 것이 바람직하다.

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Fabrication and Properties of ZnSnO3 Piezoelectric Films Deposited by a Pulsed Laser Deposition (Pulsed Laser Deposition 방법으로 증착된 ZnSnO3 압전 박막의 성장과 특성 평가)

  • Park, Byeong-Ju;Yoon, Soon-Gil
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.27 no.1
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    • pp.18-21
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    • 2014
  • Because the Pb-based piezoelectric materials showed problems such as an environmental pollution. lead-free $O_3$ materials were studied in the present study. The $O_3$ thin films were deposited at $640^{\circ}C$ on $Pt/Ti/SiO_2$ substrate by pulsed laser deposition (PLD) and were annealed for 5 min at $750^{\circ}C$ using rapid thermal annealing (RTA) in nitrogen atmosphere. Samples annealed at $750^{\circ}C$ showed a smooth morphology and an improvement of the dielectric and leakage properties, as compared with as-grown samples. However, electrical properties of the $O_3$ thin films obtained in the present study should be improved for piezoelectric applications.

Characteristics of Output Energy and Optical Parameters in Welding of Braun Tubes by Pulsed Nd:YAG Laser (펄스 Nd:YAG 레이저에 의한 브라운관 부품의 용접시 빔의 출력특성과 광학변수)

  • Kim Jong-Do;Ha Seung-Hyup
    • Journal of Korean Society of Laser Processing
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    • v.8 no.1
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    • pp.27-37
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    • 2005
  • During laser spot welding of the braun tube electron gun, phenomena such as serious spattering and oxidative reaction, etc. were occurred. The spatter occurred from weld pool affects the braun tube, namely it blocks up a very small hole on the shadow mask and causes short circuit between two poles of the electron gun. We guessed that high power density and oxidative reaction are main sources of these problems. So, we studied to prevent and to reduce spatter occurring in spot welding of the braun tube electron gun using pulsed Nd:YAG laser. The characteristics of laser output power was estimated, and the loss of laser energy by optical parameter and spatter was measured by powermeter. The effects of welding parameters, laser defocused distance and incident angle, were investigated on the shape and penetration depth of the laser welded bead in flare and flange joints. From these results, the laser peak power was a major factor to control penetration depth and to occur spatter. It was found that the losses of laser energy by optic parameter and sticked spatter affect seriously laser weldability of thin sheets.

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Analytic Study on Pulsed-Laser Polishing on Surface of NAK80 Die Steel (펄스레이저에 의한 NAK80 금형강 표면연마의 해석적 연구)

  • Kim, Kwan-Woo;Kim, Seung-Hwan;Cho, Hae-Yong
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.14 no.6
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    • pp.136-141
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    • 2015
  • Laser surface polishing is a polishing method for improving surface roughness using an integrated laser beam. Using a laser for surface polishing can improve the surface condition without physical contact or chemical action. Laser polishing has mainly been used to polish the surface of diamond or optical articles, such as lenses and glasses. Recently, diverse studies on laser polishing for metals have been conducted. The analytic study of laser surface polishing has been conducted with experimental trials for comparison, so that the proper conditions for laser polishing can be recommended. In this study, laser surface polishing was simulated in order to predict the heat-affected zone on the die steel depending on the power of the pulsed laser. The simulated results were verified by comparing them to those of the experimental trials. Through this study, therefore, the application of FEM to the selection of appropriate laser conditions could be possible.

The Structural Characteristic and Surface Morphology of ZnO Thin Films by Pulsed Laser Deposition (PLD를 이용한 ZnO 박막의 구조적 특성과 표면의 형태에 관한 연구)

  • Kim, Jae-Hong;Lee, Kyoung-Cheol;Lee, Cheon
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.52 no.6
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    • pp.231-234
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    • 2003
  • ZnO thin films on (100) p-type silicon substrates have been deposited by pulsed laser deposition(PLD) technique using an Nd:YAG laser with a wavelength of 266nm. The influence of the deposition parameters, such as oxygen pressure, substrate temperature and laser energy density variation on the properties of the grown film, was studied. The experiments were performed for oxygen gas flow rate of 100~700 sccm and substrate temperatures in the range of 200~$500^{\circ}C$. We investigated the structural and morphological properties of ZnO thin films using X-ray diffraction(XRD), scanning electron microscopy(SEM) and atomic force microscopy(AFM).

Characteristics of ZnO Thin Films Grown on p-type Si and Sapphire Substrate by Pulsed Laser Deposition

  • Lee, K. C.;Lee, Cheon
    • KIEE International Transactions on Electrophysics and Applications
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    • v.3C no.6
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    • pp.241-245
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    • 2003
  • ZnO thin films on (l00) p-type Si and sapphire substrates have been deposited by a pulsed laser deposition technique using an Nd:YAG laser with a wavelength of 266 nm. The influence of the deposition parameters such as oxygen pressure, substrate temperature and laser energy density on the properties of the grown films was studied. The experiments were performed for substrate temperatures in the range of 200∼50$0^{\circ}C$ and oxygen pressure in the range of 100∼700 sccm. All of the films grown in this experiment show strong c-axis orientation with (002) textured ZnO peak. With increasing substrate temperature, the FWHM (full width at half maximum) and surface roughness were decreased. In the case of using sapphire substrate, the intensity of PL spectra increased with increasing ambient oxygen flow rate. We investigated the structural and morphological properties of ZnO thin films using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Modeling of Pulsed Laser Heating of Tissue: Implications or Skin Resurfacing (Pulsed Laser를 이용한 생체조직 가열을 위한 모델링 : Skin Resurfacing을 위한 연관성)

  • Kwon, Y.H.;Rastegar, S.
    • Proceedings of the KOSOMBE Conference
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    • v.1997 no.11
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    • pp.375-379
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    • 1997
  • Pulsed Er:YAG and $CO_2$ lasers induced temperature rise of tissue are studied using axisymmetric, two-dimensional, and transient Pennes' bio-heat equation or the implications of skin resurfacing. Model results indicate that Er:YAG laser induced temperature has much higher but more shallow distribution in tissue than that of the $CO_2$ laser because of its higher absorption coefficient. The increase of repetition rate does not affect the temperature rise too much because these laser modalities have much shorter heat diffusion time than the temporal length of each off-pulse. This model works as a tool to understand the photothermal effect in the laser-tissue interaction.

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