• Laser Solutions
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• v.14 no.4
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• pp.14-20
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• 2011

The advantage of using lasers for through silicon via (TSV) drilling is that they allow higher flexibility during manufacturing because vacuums, lithography, and masks are not required; furthermore, the lasers can be applied to metal and dielectric layers other than silicon. However, conventional nanosecond lasers have disadvantages including that they can cause heat affection around the target area. In contrast, the use of a picosecond laser enables the precise generation of TSVs with a smaller heat affected zone. In this study, a comparison of the thermal and crystallographic defect around laser-drilled holes when using a picosecond laser beam with varing a fluence and repetition rate was conducted. Notably, the higher fluence and repetition rate picosecond laser process increased the experimentally recast layer, surface debris, and dislocation around the hole better than the high fluence and repetition rate. These findings suggest that even the picosecond laser has a heat accumulation effect under high fluence and short pulse interval conditions. To eliminate these defects under the high speed process, the CDE (chemical downstream etching) process was employed and it can prove the possibility to applicate to the TSV industry.

• Current Optics and Photonics
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• v.1 no.3
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• pp.221-227
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• 2017

To apply a square-shaped beam homogenizer to laser shock peening, it should be designed with a long working distance and by considering metal targets with various shapes and textures. For long working distances, a square-shaped beam homogenizer with a long depth of focus is required. In the range of working distance, the laser beam is required to have not only high efficiency but high uniformity, in other words, a good peening quality is guaranteed. In this study, we defined this range as the working distance for laser shock peening. We have simulated the effect of some parameters on the working distance. The parameters include the focal length of the condenser lens, pitch size of the array lens, and plasma threshold of the metal. The simulation was performed through numerical analysis by considering the diffraction effect.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.583-588
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• 2002

The purpose of the study is to evaluate fracture toughness on the Laser and the electron beam welded joints of high tensile steels (HT500, HT550, HT650) by using 3-point bend CTOD and Charpy impact test. WM (weld metal) CTOD tests have been carried out using two kinds of CTOD specimen, the Laser beam welding (108mm length, and 24mm width, and 12mm thickness) and the electron beam welding (l71mm length, and 38mm width, and 19mm thickness). WM Charpy impact specimen is a standard V-notch type, and the temperature of the experiment is changed from -45 to 20 degree of centigrade. FE-analysis is also performed in order to investigate the effect of stress-strain fields on fracture characteristics. Results of the standard V-notch Charpy test are influenced by strength mis-match effect and the absorbed energy vE depends on crack path, and The transition temperature of Laser beam welded joints is more higher than that of electron beam welded joints. Results of the 3-point bend test give low critical CTOD and the crack path is in the weld metal of al specimens. These results indicate fracture toughness characteristics of the welded joints and transition temperature of HT500 are similar both a Laser beam welded joint and an electron beam welded joint. But the fracture toughness and the transition temperature of the electron beam welded joints of HT550 and HT650 are higher than those o the Laser beam welded joints.

• Journal of Institute of Convergence Technology
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• v.5 no.2
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• pp.21-25
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• 2015

This paper proposes a fabrication process of deposited layer with micro patterns that uses a combination of a pulsed laser beam machining and an electrodeposition. This process consists of the electrodeposition and the laser beam machining. The deposited layer on metal can be selectively eliminated by laser ablation. As a result, the deposited layer with micro patterns can be fabricated without a mask. The characteristics of the deposited layer on stainless steel were investigated according to the average power and marking speed in the pulsed laser beam machining. The optimal laser beam conditions for precise micro patterning of the deposited layer were determined. Finally, the deposited copper layer with micro text was successfully fabricated by the pulsed laser beam machining.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1452-1457
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• 2004

In this paper, a method of measuring the length of defects on the wall and restructuring the defect image is proposed based on the estimation algorithm of a camera orientation which uses the declination angle of a laser slit beam. The estimation algorithm of the horizontally inclined angle of CCD camera adopts a 3-dimensional coordinate transformation of the image plane where both the laser beam and the original image of the defects exist. The estimation equation is obtained by using the information of the beam projected on the wall and the parameters of this equation are experimentally obtained. With this algorithm, the original image of the defect can be reconstructed to an image normal to the wall. From the result of a series of experiments, the measuring accuracy of the defect is measured within 0.5% error bound of real defect size under 30 degree of the horizontally inclined angle. The proposed algorithm provides the method of reconstructing the image taken at any arbitrary horizontally inclined angle to the image normal to the wall and thus, it enables the accurate measurement of the defect lengths only by using a single camera and a laser slit beam.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.193-196
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• 2003

We have developed a laser welding monitoring system to monitor laser welding process conditions such as sample feed rate, laser focal position, and laser power. A 2 ㎾ Nd:YAG CW laser beam has been applied to the welding of a stainless steel plate (SUS306) to investigate the welding monitoring. Theradiation signal from the weld pool was guided back through the focusing optics and the laser delivery fiber, and measured by a photo detector. By changing the focus of the laser beam along the z-direction, the penetration depth of the welding material has been measured. That shows the penetration depth depends on the frequency fluctuations of the plume signals which can be used in welding quality control.

• Journal of Institute of Convergence Technology
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• v.4 no.2
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• pp.41-45
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• 2014

Micro fabrication technologies of aluminium have been required to satisfy many demands in technology fields. Pulsed laser beam machining can be an alternative method to accomplish the micro machining of aluminium. Pulsed laser beam can be applied to micro machining such as micro drilling and milling. Using pulsed laser beam, the machining characteristics of aluminium in micro drilling and milling were investigated according to average power, repetition rate, moving speed of spot. The laser beam machining with the optimal conditions can achieve precise micro figures. As a result, micro pattern, text and structures on aluminium surface was successfully fabricated by pulsed laser beam machining.

• Korean Journal of Optics and Photonics
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• v.35 no.2
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• pp.49-60
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• 2024

We analyze the number of phase screens required for the simulation of a high-energy laser beam's propagation over an atmospheric channel. For high-energy lasers exceeding tens of kilowatts (kW) in power, the laser beam is mainly affected by atmospheric turbulence and thermal blooming. When using the split-step method to implement losses due to atmospheric absorption and scattering and distortion of the beam due to turbulence and thermal blooming, the number of phase screens is a critical factor in determining the accuracy and time required for the simulation. By comparing simulation results obtained using a large number of phase screens (e.g., 150 screens) under a wide range of atmospheric turbulence conditions, we provide new guidelines for the number of phase screens required for simulating the beam propagation of a high-power laser below 2.5×10⁶ W/m² (e.g., a 500-kW laser beam having a 50-cm diameter).

• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.171-179
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• 2004

Micro-stereolithography technology has made it possible to fabricate a freeform 3D microslructure. This technology is based on conventional stereolithography, in which a UV laser beam irradiates the open surface of a UV-curable liquid photopolymer, causing it to solidify. In micro-stereolithography, a laser beam of a few $\mu m$ diameter is used to solidify a very small area of the photopolymer. This is one of the key technological elements, and can be achieved by using a focusing lens. Thus, the solidification phenomena of the liquid photopolymer must be carefully investigated. In this study, the photopolymer solidification phenomena in response to variations in the scanning pitch of a focused laser beam was investigated experimentally. The effect of layer thickness on the solidification width and depth was also examined. These studies were conducted under the conditions of relatively lower laser power and relatively higher scanning speed. Moreover, the photopolymer solidification phenomena for the relatively higher laser power and lower scanning speed was investigated, too. In this case, comparing to the case of lower laser power and higher scanning speed, the photopolymer absorbed large amount of irradiation energy of the laser beam. These results were compared with those obtained from a photopolymer solidification model. From these results, a new laser-scanning scheme was proposed according to the shape of the 3D model. Samples by each method were fabricated successfully.

• Laser Solutions
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• v.2 no.2
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• pp.8-17
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• 1999

This study includes a basic feature of laser surface alloying for enhancing the surface properties of materials. Effects of laser processing parameters such as beam power, beam size, scanning speed on the shape and composition of alloyed layer was simulated in case of moving beam conditions (2-dimensional numerical methods). Simulated results were compared with experiments, in which the plasma coating of 80% Ni ＋ 20% Cr deposited on the SS41 substrate was remelted with CO2 laser with Gaussian energy distribution. Simulation and experiments revealed that the shape (dimension)and composition of laser alloyed layer were strongly dependent upon the process parameters, especially interaction time (travel speed) as compared to beam diameter, beam power and absorptivity. The shape and composition of alloyed layervaried more or less exponentially with parameters.