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열적 메커니즘에 의한 펄스레이저 어블레이션 현상의 수치계산
오부국(Bukuk Oh),김동식(Dongsik Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
High-power pulsed laser ablation under atmospheric pressure is studied utilizing numerical and<br/> experimental methods with emphasis on recondensation ratio, and the dynamics of the laser induced vapor<br/> flow. In the numerical calculation, the temperature pressure, density and vaporization flux on a solid substrate<br/> are first obtained by a heat-transfer computation code based on the enthalpy method, and then the plume<br/> dynamics is calculated by using a commercial CFD package. To confirm the computation results, the probe<br/> beam deflection technique was utilized for measuring the propagation of a laser induced shock wave.<br/> Discontinuities of properties and velocity over the Knudsen layer were investigated. Related with the analysis<br/> of the jump condition, the effect of the recondesation ratio on the plume dynamics was examined by<br/> comparing the pressure, density, and mass fraction of ablated aluminum vapor. To consider the effect of mass<br/> transfer between the ablation plume and air, unlike the most previous investigations, the equation of species<br/> conservation is simultaneously solved with the Euler equations. Therefore the numerical model computes not<br/> only the propagation of the shock front but also the distribution of the aluminum vapor. To our knowledge,<br/> this is the first work that employed a commercial CFD code in the calculation of pulsed ablation phenomena.
오부국(Bukuk Oh),김동식(Dongsik Kim),김재구(Jaegu Kim),이제훈(Jae-hoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
A numerical tool for simulating the fs laser ablation of metals is developed. Two temperature model is introduced to predict the ablation rate and the crater shape of metals. Phase explosion and spallation are considered as the ablation schemes for high fluence and low fluence regime, respectively. The ultrashort thermoelastic model is used in the low fluence regime, to obtain the laser-induced stress field. The results show that the thermoelastic stress generated within the target can exceed the yield stress of the material at a relatively low fluence. Numerical results obtained by the adapted models are compared with the experimental ones, Cu, Ni.
피코초 레이저를 이용한 고세장비 미세 홀가공의 실험적 연구
오부국,김종기,김두영,이승기,정수화,홍순국,Oh, Bukuk,Kim, Jongki,Kim, Dooyoung,Lee, Seungkey,Jeong, Soohoa,Hong, Michael 한국레이저가공학회 2015 한국레이저가공학회지 Vol.18 No.2
Pressure-drop in a micro-channel is critical when a hole diameter is less then 100um with the high aspect ratio, more than 40. To minimize these pressure loss for micro-channel applications is important and there would be the best hole diameter, taper angle, and their combinations. In this work, the parametric study for laser drilling of anodized material is conducted to obtain the micro-channel hole with high aspect ratio.
오부국,김동식 한국레이저가공학회 2003 한국레이저가공학회지 Vol.6 No.3
Pulsed laser ablation is important in a variety of engineering applications involving precise removal of materials in laser micromachining and laser treatment of bio-materials. Particularly, detailed numerical simulation of complex laser ablation phenomena in air, taking the interaction between ablation plume and air into account, is required for many practical applications. In this paper, high-power pulsed laser ablation under atmospheric pressure is studied with emphasis on the vaporization model, especially recondensation ratio over the Knudsen layer. Furthermore, parametric studies are carried out to analyze the effect of laser fluence and background pressure on surface ablation and the dynamics of ablation plume. In the numerical calculation, the temperature, pressure, density, and vaporization flux on a solid substrate are obtained by a heat-transfer computation code based on the enthalpy method. The plume dynamics is calculated considering the effect of mass diffusion into the ambient air and plasma shielding. To verify the computation results, experiments for measuring the propagation of a laser induced shock wave are conducted as well.
압밀 금속 마이크로 입자의 펄스 레이저 ABLATION에 의한 나노입자 합성
장덕석,오부국,김동식 한국레이저가공학회 2002 한국레이저가공학회지 Vol.5 No.2
This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ns, fluence 0.8∼2.0 J㎠). Microparticles of mean diameter 18-80 μm are ablated in the ambient air. The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.