• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.186-191
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• 2008

A phase retrieval method using an error reduction algorithm is developed for reconstructing a wavefront aberration of an 100-TW Ti:sapphire laser pulse from the measurement of a focal spot. The phase retrieval method can successfully reconstruct a wavefront aberration of a 100-TW Ti:sapphire laser pulse, and the reconstructed wavefront aberration shows a good agreement with the wavefront aberration measured with a wavefront sensor. The effect of the dynamic range and the intensity noise on the reconstruction is also investigated in reconstructing a wavefront aberration of an 100-TW Ti:sapphire laser pulse.

• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.13-21
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• 1997

This paper describes the effectiveness of laser pulse shaping in eliminating weld defects such as porosity, cracks and undercuts in pulsed Nd:YAG Laser welding. A large porosity was formed in a keyhole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 303 with about 0.3%s. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S. through high speed video photographing technique. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.

• Current Optics and Photonics
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• v.7 no.6
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• pp.732-737
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• 2023

A high-power Yb-doped femtosecond (fs) fiber laser at a repetition rate of 1.83 GHz is reported. By employing a 5-stage repetition rate multiplier, the repetition rate of the mode-locked master oscillator was multiplied from 57.1 MHz to 1.83 GHz. The ultrashort pulse output at 1.83 GHz was amplified in a two-stage Yb-doped fiber amplifier, leading to >100 W of fs laser output with a pulse duration of 290 fs. The theoretical pulse width along the fiber was simulated, showing that it was in good agreement with experimental results. Further improvement in power scaling is discussed.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.777-783
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• 2001

This paper is mainly concerned with the state of the practical developments of a constants PWM bridge type resonants DC-DC suitable converter for Nd:YAG Laser with a Microprocessor. (PIC16C54 & 8051) The use of IGBT power supply with feedback control of flashLamp currents imparts a advantages to Nd:YAG Laser for materials processing. these include the alility to tailor the pulseshape and modify pulse parameters on a pulse- by pulse basis. And Correct choice of pulseshape can enhance the repeatability of the process. as higher power IGBT became available, act ive pulseforming power supplies will find greater user in deep hole drilling machine By Using certain control tecniques, utililized in designing Pic16c54 from Microchip technology and Intel 8051, also Mornitoring from Microsoft Visual Basic 5, And it allowed us to designed and fabricate ahigh repel it ion rate and high power(HRHP) pulsed Nd:YAG laser system, As a result of that, the current pulsewidth could be contort led 200s to 350s(step 50s) , and the pulse repetition rate could be adjusted 500pps to 1150pps. In addition, in the case of one laser head consisting of a Nd:YAG laser rod and two flashlamps , the maximum laser output of 240w was produced at the condition of 350s and 1150pps, and that of about 480w was generated at the same condition when two laser heads were arranged in cascade.

• Laser Solutions
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• v.13 no.4
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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.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.91-96
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• 2015

The laser-arc hybrid welding of SS400 steel was carried out with the use of disk laser equipment of 6.6kW maximum power and MAG equipment of pulse mode. Parameter regarding heat input is one of the most important factors that directly affect penetration characteristics and welding defect. Therefore in this study, the effects of laser power, welding speed and current, voltage and pulse correction were investigated. As experiment result, it was found that the lower heat input, the more likely humping bead is formed at the back, and such humping bead could be suppressed by increasing laser power and arc current or decreasing welding speed, thus increasing heat input. Also deep penetration could be achieved by reducing arc voltage or pulse correction parameter in the same welding condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.74-77
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• 2000

A pulsed Nd:YAG laser has been used in a wide variety of fields : measuring, material processing and so on. In a material processing, it is very important to control the laser energy density. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this study, pulsed Nd:YAG laser system was designed and manufactured to control the laser output usefully and easily. This system adopted the sequential charge and discharge circuit is controlled by 80196 micro- processor. As a result, it is found that laser output is controlled minutely by changing laser input and pulse repetition rate, and usefully by using 80196 microprocessor.

• Laser Solutions
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• v.9 no.3
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• pp.15-21
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• 2006

A Polypropylene (PP) film was ablated using a femtosecond laser with a center wavelength of 785 nm, a pulse width of 184 fs and a repetition rate of 1 kHz. Increments of both pulse energy and the shot number of pulses lead to co-occurrence of photochemical and thermal effect, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated PP films were imaged by a scanning electron microscope (SEM) and measured a 3D optical measurement system (NanoFocus). And, the oxygen transmission rate (ORT) of periodically laser-ablated PP film were characterized by oxygen permeability tester for modified atmosphere packaging (MAP) of fresh fruit and vegetable. Our results demonstrate that femtosecond pulsed laser is efficient tools for breathable packaging films in modifying the flow of air and gas into and out of a fresh produce container, where the micropatterns are specifically tailored in size, location and number which are easily controlled by laser pulse energy and pulse patterning system.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.99-104
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• 2010

Magnesium and magnesium alloys, the lightest structural materials, have been received plenty of global attention recently. These alloys could be applied in various fields, especially the electronics industry, because of their excellent electromagnetic interference shielding. However, the welding technique of magnesium alloys has not been established. This study is related to the welding of AZ31B magnesium alloy by a short-pulsed a Nd:YAG laser. Two types of pulse waves, square pulse and variable pulse, were used to control weld defects. Results show that the crack and porosity, generated in the weld, had not been controlled by general square pulse. But through the application of variable pulse, the defects could be prevented and the good weld zone was obtained.

• Laser Solutions
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• v.12 no.3
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• pp.18-22
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• 2009

Experimental results for the laser shock peening of stainless steels, duplex stainless steel and STS304, for the enhancement of surface hardness are reported. A high power Nd:YAG laser (532 nm, 2nd harmonics) was used to irradiate the workpiece in water at the irradiances of 5, 10, $15\;GW/cm^2$. The surface of a workpiece was covered with Fe or Al foil for protection of the original surface and reduction of laser reflection. The laser pulse densities were varied from $25\;pulse/mm^2$ to $75\;pulse/mm^2$. In the case of the STS304, the surface hardness increased with increasing pulse density and the maximum increase of about 29% was achieved using Fe foil at $10\;GW/cm^2$ and $75\;pulse/mm^2$ conditions. The maximum increase in surface hardness of duplex stainless steel was about 8% at $10\;GW/cm^2$ and $75\;pulse/mm^2$ with also Fe foil. In the case of the Al foil, less increase of surface hardness was obtained, possibly due to the thermal expansion effect.