• 한국레이저가공학회지
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• 제13권2호
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• pp.10-16
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• 2010

Laser-assisted machining is dependent on absorbed energy density into workpiece. Generally, the absorptivity of laser beam is dependent on wave length of laser, materials, surface roughness, etc. Various shapes and energy densities for beam irradiation can be used to laser-assisted machining. In this thesis, efficient method of heat source modeling was developed and designed by using one fundamental experimental trials. And then, laser-assisted machining of rod-shaped cast iron was simulated by using commercial FEM code MARC. Simulations and experiments with various conditions were carried out to determine suitable condition of pre-heating for laser-assisted turning process. Temperature distribution of cutting zone could be predicted by simulation.

• 한국레이저가공학회지
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• 제11권3호
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• pp.5-9
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• 2008

The effect of a laser peening on the surface residual stress of SUS 304 was investigated using a second harmonic Nd:YAG laser beam. The energy density and the diameter of the laser beam were $400mJ/mm^2$ and about 1mm, respectively. According to the test results, the effect of a laser peening for improving the surface residual stress was not big enough to induce a high compressive stress on the SUS 304 surface. This is thought to be attributed to the small radius of the laser beam used in this study, even though its energy density is big enough. From this study, it can be concluded that to induce a recognizably high compressive stress on a metal surface, the energy density as well as the size (diameter) of the laser beam should be large enough to generate surface plasma with a high energy to have a big impact to a metal surface.

• 한국전기전자재료학회논문지
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• 제13권1호
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• pp.60-65
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• 2000

The structural and electrical characteristics of PLZT thin films fabricated onto Pt/Ti/SiO\ulcorner/Si substrates by a pulsed laser deposition were investigated to develop the high dielectric thin films were fabricated with different energy density by pulsed laser deposition. This PLZT thin films of 5000 thickness were crystallized at 600 $^{\circ}C$, 200 mTorr O\ulcorner pressure for 2 J/$\textrm{cm}^2$ laser energy density, the arain structure was transformed from planar to columnar grain. It was clearly noted from the SEM observations that oxygen pressured laser powers affect microstructures of the PLZT thin films. 14/50/50 PLZT this film showed a maximum dielectric constant value of $\varepsilon$\ulcorner=1289.9. P-E hysteresis loop of 14/50/50 PLZT thin film was flim ferro-electric. Leakage current density of 14/50/50 PLZT thin film was 10\ulcorner A/$\textrm{cm}^2$.

• 한국분말재료학회지
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• 제8권4호
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• pp.239-244
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• 2001

To investigate the effect of process parameters on selective laser sintering of Cu/polyamide mixed powder, Cu/polyamide mixed powder was sintered by selective laser with changing laser power and scanning speed. The properties of sintered body were evaluated by measuring the density and tensile strength, and analysis of XRD, FT-Raman and microstructure. With an increase in the laser power, the density and ultimate tensile strength of sintered Cu/polyamide body increase and then decrease. The maximum values of the density and ultimate tensile strength were decreased with increasing laser scanning speed. These changes were concerned with the difference of irradiation energy of laser into the powder layer. It was considered that the change of the mechanical property of the sintered body with irradiation energy of laser is due to the changes of amount of copper particle and property of polyamide.

• Journal of Welding and Joining
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• 제11권1호
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• pp.52-61
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• 1993

Laser welding of ASTM no. 1060 Al plate with a pulsed Nd: YAG laser of 200W average power was performed for end capping of KMRR nuclear fuel elements In this research, we performed basic welding experiments. Firstly, laser output parameters which affect laser welding parameters were studied by changing laser input parameters for effective welding of 1060 Al plates. We found that laser power density and pulse energy are important parameters for smooth bead shape. Secondly, welding parameters which affect weld width-to-depth ratio were studied by changing power density and pulse energy, shielding gas, and defocusing. We found that power density must be higher than 0.3 Mw/cm$^{2}$ pulse energy must be higer than 3 J. travel speed must not exceed 200mm/sec, laser focus must be existed beneath 2-3mm from plate surface and helium is proper shielding gas. Thirdly, we studied the weld defects of Al-1060 such as crack and porosity in lap-joint welding. We designed new welding geometry for crack free welding of Al-1060 plates, and obtained crack free weldment but with lack of fusion. However, with Ti, Zr grain refiner elements, we can weld Al plates without solidification hot crack. Finally, we studied the origin of porosity by changing shielding gas. And we found that porosity was resulted from entrapment of shielding gas by the collapsing keyhole.

• 한국레이저가공학회지
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• 제13권4호
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• pp.7-13
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• 2010

Today, the most common process for generating Through Silicon Vias (TSVs) for 3D ICs is Deep Reactive Ion Etching (DRIE), which allows for high aspect ratio blind holes with low surface roughness. However, the DRIE process requires a vacuum environment and the use of expensive masks. The advantage of using lasers for TSV drilling is the higher flexibility they allow during manufacturing, because neither vacuum nor lithography or masks arc required and because lasers can be applied even to metal and to dielectric layers other than silicon. However, conventional nanosecond lasers have the disadvantage of causing heat affection around the target area. By contrast, the use of a picosecond laser enables the precise generation of TSVs with less heat affected zone. In this study, we conducted a comparison of thermalization effects around laser-drilled holes when using a picosecond laser set for a high pulse energy range and a low pulse energy range. Notably, the low pulse energy picosecond laser process reduced the experimentally recast layer, surface debris and melts around the hole better than the high pulse energy process.

• 전자공학회논문지A
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• 제33A권6호
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• pp.172-177
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• 1996

We have characterized XeCl excimer-laser-induced crystallization of thin amorphous silicon films deposited by PECVD (${\alpha}$-Si:H) and LPCVD (${\alpha}$-Si). The electrical properties, surface roughness and crystallinity of crystallized thin films have been measured. The dc conductivities, crystallinity andsurface roughness of the films increased as the laser energy density and shot density were increased. The properties of laser annealed films deposited by LPCVD were better than those of thin films deposite by PECVD. We have also found that the multiple shots with relative low energy density were more benifical to the improsvement of surface roughness than the single shot with high energy density preserving the crystallinity.

• 한국정밀공학회지
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• 제26권12호
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• pp.41-46
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• 2009

• Journal of the Optical Society of Korea
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• 제12권3호
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• pp.178-185
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• 2008

Recent progress in high power lasers enables us to access a regime of high-energy-density and/or ultra-strong fields that was not accessible before, opening up a fundamentally new physical domain which includes laboratory astrophysics and laser nuclear physics. In this article, new applications of high-energy and ultra-intense laser will be reviewed.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.42-47
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• 2009

The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.