• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.231-232
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.107-108
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• 2010

• Journal of the Korean Society of Industry Convergence
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• v.22 no.3
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• pp.243-250
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• 2019

The nanosecond laser assisted ablation have been investigated. The biocompatable polymer PMMA was employed as the target material and the two distinctive surface conditions were test. The first surface condition is a dry surface for which the target surface is exposed to air and the second surface condition is the wet surface for which the target surface is covered with dehydrated water. The ablation volume, the laser induced acoustic wave, the laser induced plasma were investigated for both wet and dry condition. The nanosecond laser pulse ablatied more on the wet surface compared to the dry surface. The enhanced ablation of wet surface is attributed to the confined acoustic wave and the laser-induced plasma in the liquid layer.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.108-115
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• 2009

Although nanosecond pulsed laser drilling and milling are rapid and non-wear processes in micromachining, the quality cannot meet the precision standard due to the recast layer and heat affected zone. On the other hand, electrical discharge machining (EDM) is a well-known high precision machining process in micro scale; however, the low material removal rate (MRR) and tool wear remain as drawbacks. In this paper, hybrid process of laser beam machining (LBM) using nanosecond pulsed laser and micro EDM was studied for micro drilling and milling. While the quality of the micro structure fabricated by this hybrid process remains as high as direct EDM, the machining time and tool wear can be reduced. In addition, variable depth of layer was introduced as an effective method improving efficiency of hybrid milling.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.2 s.191
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• pp.134-139
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• 2007

Usually nanosecond pulsed laser processing of metal is mainly affected by the thermal ablation. Many studies of the theoretical analysis and modeling to predict the laser ablation of metal are suggested on the basis of the photothermal mechanism at higher laser fluence. In this paper, we investigate the etching depth and laser fluence of laser ablation of copper foils and propose the simplified SSB Model(Srinivasan-Smrtic-Babu model) to study the photothermal effect of nanosecond pulsed laser ablation. The experimental results show that the photothermal ablation of the 355nm DPSS $NdYVO_{4}$ laser is useful to process the copper thin foils.

• Laser Solutions
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• v.6 no.3
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• pp.37-45
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• 2003

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.

• Laser Solutions
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• v.14 no.3
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• pp.7-11
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• 2011

As an active emission display using emissive polymer has had much attention recently, needs for a selective patterning of emissive layer for those displays have been increased abruptly. Therefore, the various laser sources in terms of its wavelength has been used for laser direct patterning. In this work, the feasibility of those processes is examined using numerical analysis and the experimental investigation. A sample has multi-layered structure, emissive polymer on aluminum which is deposited on a glass substrate. Key factors for optimizing the laser patterning of the emissive polymer are considered into the control of ablation products, large-sized particle, and the choice of the appropriate wavelength for minimizing the heat affected zone and the remnant layer.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.118.1-118.1
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• 2016

The laser surface modification has been reported for its functional applications for improving tribological performance, wear resistance, hardness, and corrosion property. In most of these applications, continuous wave lasers and pulsed lasers were used for surface melting, cladding, alloying. Since flexibility in processing, refinement of microstructure and controlling the surface properties, technology utilizing lasers has been used in a number of fields. Especially, femtosecond laser has great benefits compared with other lasers because its pulsed width is much shorter than characteristic time of thermal diffusion, which leads to diminish heat affected zone. Moreover, laser surface engineering has been highlighted as an effective tool for micro/nano structuring of materials in the bio application field. In this study, we applied femtosecond and nanosecond pulsed laser to treat biometals, such as Mg, Mg alloy, and NiTi alloy, by heating to improve corrosion properties and functionalize their surface controlling cell response as implantable biomedical devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.804-812
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• 2003

This paper introduces optical methods for in-situ measurement of surface temperature and pressure transient in thermal processes having nanosecond time scales. In the temperature measurement, a p -Si thin film whose refractive index is calibrated as a function of temperature is embedded beneath the sample surface and the photothermal reflectance is monitored for estimating the surface temperature. The pressure transients are measured using the photoacoustic optical deflection method. The experimental technique is used to analyze the nanosecond laser induced vaporization process that is central to numerous engineering and bio-medical applications. Based on the experimental results, discussions are made on the experimental technique and the physical mechanisms of laser-driven explosive vaporization phenomena.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.10
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• pp.1089-1095
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• 2012

Laser beam machining (LBM) using nanosecond pulsed laser is widely known to be rapid and non-wear process for micromachining. However, the quality itself cannot meet the precision standard due to the recast layer and heat affected zone. In this paper, a fabrication method for machining micro features in stainless steel using a hybrid process of LBM using nanosecond pulsed laser and electrochemical etching (ECE) is reported. ECE uses non-contacting method for precise surface machining and selectively removes the recast layer and heat affected zone produced by laser beam in an effective way. Compared to the single LBM process, the hybrid process of LBM and ECE enhanced the quality of the micro features.