• Journal of Welding and Joining
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• v.24 no.1
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• pp.88-92
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• 2006

Laser-rotating arc hybrid welding was introduced by combining $CO_2$ laser and rotating gas metal arc welding. While the arc rotation enhances the weld pool motion, it reduces the undercut formation which is one of most critical weld defects in the conventional laser-arc hybrid welding. This research investigated the bead characteristics according to the welding parameters such as frequency of rotation, welding voltage, shielding gas composition and interspacing distance between laser and we. The welding parameters were selected to reduce spatter generation and ensure sound weld beads fur bead welding and butt welding with various joint gaps. Gap bridging ability was improved, such that the sound weld beads were achieved for butt joint with up to 2mm joint sap, with no adjustment of CTWD(Contact tip-to-workpiece distance) and electrode diameter.

• Korean Journal of Acupuncture
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• v.22 no.2
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• pp.163-181
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• 2005

Objective: The purpose of this study is to review research papers on low level laser therapy (LLLT) and to improve the knowledge of LLLT field. Methods: For introduction, laser characteristics, including wavelength, medium, beam size, power, and unit power were explained. In order to understand LLLT, tissue optics and light-biomatter interaction were briefly mentioned. We reviewed 21 Korean papers on laser acupuncture and LLLT on the viewpoint of laser apparatus. Results and Conclusion: We found that the description of laser apparatus employed for LLLT experiments were not fully written. Laser wavelength and power which are the most crucial parameters, were omitted in several papers. No paper had information on beam size. In order to have high efficacy, laser should be used with proper laser parameters. Conditions of irradiation area or acupoints should be considered too. Some future technology on laser acupuncture were mentioned.

• Journal of Welding and Joining
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• v.9 no.1
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• pp.32-39
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• 1991

A 200W pulsed Nd: YAG laser for fine welding was developed. The important laser parameters such as laser peak power, average power, pulse width, and pulse energy for welding were studied. In order to obtain the sufficient laser power density for welding, thermal lensing effects were analyzed and a laser resonator with laser beam divergence was designed. The power supply unit was designed to support up to 7kW input. The pulse control unit was developed using a GTO thyristor and could control over 100kW input power to obtain 3.5kW peak power laser. Also due to the GTO thyristor the pulse width could be varied continuously from 0.1 to 20 msec and maximum repetition rate was as high as 300pps.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.5-5
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• 2010

The depth of the object pointed by the laser beam is computed depending on the pixel position on the CCD There involved several number of internal and external parameters such as inter-pixel distance, focal length, position and orientation of the system components in the depth measurement error. In this paper, it is shown through the error sensitivity analysis of the parameters that the most important parameters in the sense of error sources are the angle of the laser beam and the inter pixel distance. Also, the calibration technique to minimize their effect for the depth computation is proposed.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.54-61
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• 2005

A simulator for virtual laser machining is developed to help understanding and predicting the effects of machining parameters on the final machined results. Main program is based on the model for polymer ablation with short pulse excimer lasers. Version f of the simulator is built using Visual Fortran to make the user work under visual environment such as Windows on PC, where the important machining parameters can be input via dialog box and the calculated results for machined shape, beam fluence, and temperature distribution can be plotted through the 2-D graphics windows. Version II of the simulator is built using HTML, CGI and JAVA languages, allowing the user to control the input parameters and to see the results plot through the internet.

• Journal of Oral Medicine and Pain
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• v.21 no.1
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• pp.183-196
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• 1996

The author examined the clinical and histological changes on the dorsal tongue mucosa of adult Sprague-Dawley rats after lasing by pulsed Nd:YAG laser. The dorsal tongue was lased for 3 seconds by 1.5, 2.0, 2.5, 3.0, 3.5, 4.0W and 10, 15, 20, 20pps. After tissue changes were observed clinically, the excised samples were observed histologically and the width of tissue destruction was analyzed quantitatively under the Confocal laser microscope respectively. The following results were obtained : 1. Whitening of peripheral tissue was observed more as increasing pulsed per second (Hz) below power 2.5W and observed at all parameters above power 3.0W. 2. Charring of mucosal surface was observed at all parameters but mild at parameters below power 2.0W. 3. The destruction of epithelium was observed at all parameters and tissue destruction was extended to lamina propria at higher pulses per second. 4. The width of tissue destruction was more widening as increasing energies per pulse (p<0.001) and the narrowest at 20Hz than 10Hz, 15Hz and 30Hz(p<0.05). As the above results, author suggests power below-3.5W and 20Hz as the lasing parameters for oral soft tissue therapy.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.250-251
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• 2006

It is known that powder characteristics including particle size and distribution, particle shape, and chemical composition are important parameters which influence direct laser sintering of metal powders. In this paper, we introduce a first order kinetics model for densification of steel powders during laser sintering. A densification coefficient (K) is defined which express the potential of different powders to be laser-sintered to a high density dependent on their particle characteristics.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.475-476
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• 2009

• Proceedings of the Korean Society of Laser Processing Conference
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• 2001.05a
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• pp.86-91
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• 2001

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.743-746
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• 2000

The removal of contaminants of silicon wafers has been investigated by various methods. Laser cleaning is the new dry cleaning technique to replace wafer wet cleaning in the near future. A dry laser cleaning uses inert gas jet to remove contaminant particles lifted off by the action of a KrF excimer laser. A laser cleaning model is developed to simulate the cleaning process and analyze the influence of contaminant particles and experimental parameters on laser cleaning efficiency. The model demonstrates that various types of submicrometer-sized particles from the front sides of silicon wafer can be efficiently removed by laser cleaning. The laser cleaning is explained by a particle adhesion model. including van der Waals forces and hydrogen bonding, and a particle removal model involving rapid thermal expansion of the substrate due to the thermoelastic effect. In addition, the experiment of wafer laser cleaning using KrF excimer laser was conducted to remove various contaminant particles.