• Laser Solutions
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• v.15 no.1
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• pp.15-19
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• 2012

The fabrication of internal diffraction gratings with photoinduced refractive index modification in transparent materials was demonstrated using low-density plasma formation excited by a femtosecond (130 fs) Ti: sapphire laser (${\lambda}_p$=800 nm). The refractive index modifications with diameters ranging from $1{\mu}m$ to $3{\mu}m$ were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than $2.0{\times}10^{13}W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1270-1273
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• 1997

We have investigated the latchup characteristics of BL/BILLI retrograde twin well CMOS that has the high energy ion implanted buried layer to intend for more improvement of latchup compare to conventional retrograde well and BILLI structures. We explored the dependence of various latchup characteristics such as n+ trigger latchup and p+ trigger latchup on the buried layer implant doses. We show various DC latchup characteristics that allow us to evaluate each technology and suggest guidelines for the reduction of latchup susceptibility.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1292-1297
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• 1997

본 연구에서는 latch-up 개선책의 일환으로 개발중인 매립층을 갖는 retrograde well의 형성기술과 더불어 공정 단순화를 목적으로 개발된 BILLI (Buried Implanted Layer for Lateral Isolation) well 구조[1]에 대한 공정 유기 결함을 분석하고 그에 의한 소자 열화 특성을 분석 하였으며 그 개선책을 제시 하고자 하였다. 매립층 형성에 의한 유기결함은 접합 누설전류와 Gate oxide 신뢰성을 열화 시켰으나 이온주입 후 $1000^{\circ}C$ 이상의 온도에서 10sec 정도의 RTP anneal에 의해 그 소자 특성이 개선되며 표면 결함이 감소함을 알 수 있었다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.9-17
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• 2020

In this study, the surface changes of titanium alloy using laser surface treatment and the surface analysis using laser-induced plasma spectroscopy were carried out. The laser surface treatment induced changes in surface roughness and the diffusion of atmospheric elements. Excessive melting or less melting caused roughness changes, but when moderate levels of energy were applied, a smoother surface could be obtained than the initial surface. In the process, the diffusion of atmospheric elements took place. To analyze the diffusion of atmospheric elements with respect to surface morphology, the surfaces were re-shaped with grinding. In this experimental conditions, the effect of plasma formation by surface roughness was identified. Compensated plasma signals for the material properties were obtained and analysed by removing the background plasma signal.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.60-65
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• 2013

Ar, $N_2$, and He are the conventional kind of shield gas that are used for laser welding. Many researches on the impact of laser welding shield gas have been done, and it is on going until now. However, there are few studies that analyze the changes and differences of the plasma emission signal. Therefore, in this study, we evaluated the change in the penetration characteristics according to the type of shield gas during fiber laser welding impacts to the plasma signal. As a result, if was checked that the difference in molecular weight of Ar, $N_2$, and He affects to the amount of spatter, and also found that the measured plasma radiation signal changes similar to the order of the molecular weight of the gases. Especially, clear change on the signal intensity per each shield gas was measured through RMS, and found that the shield gas was nothing to do with the FFT analyzed result.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.109-115
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• 2002

In this study high power Nd:YAG laser welding of structural steel was investigated. For the test steel blocks of $50{\times}50{\times}200mm$ were cut and machined, and bead-on-plate weld was made on the machined surface. Argon, nitrogen, helium, dry air or mixed gases were used to find the effect of shielding conditions on the bead formation. Results demonstrated that there were Fe I rich region and Fe II rich region in the laser induced plasma column based on the spectral analysis with S-2000 field spectrometer The Fe I region was located at the root of the column near keyhole opening. On the other hand, Fe II region was found at the middle of the plasma column. In the Nd:YAG laser welding, Fe I region emitted continuum which had peak value at wave length of around 710nm, and Fe II region had the peak at 580nm. In the welding of steel by $CO_2$ laser, however, no continuum was observed. There showed two groups of strong spikes in the $CO_2$ laser welding; the first group was displayed at the wave band of 450-560nm. This spike group emitted stronger intensity of light and sharper peaks than those group at 680-800nm.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.33 no.5
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• pp.173-180
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• 1984

The spectra of scattering light fromlaser-produced plasma near its fundamental and second harmonic wavelength were observed respectively by means of spectroscopic technique. The experimental results and the generation mechanism of nonlinear effects such as the second garmonics and the brillouin scattering were analysed theoretically. The spectra of reflected laser light became wider than that of incident laser light. And the peak of spectrum of reflected light shifted to red-side from that of incident light. The second harmonic light is generated from the nonlinear interaction of the incident laser light and the electron plasma wave excited in resonance region by the oblique incidence of laser light to the plasma. The Brillouin backscattering from laser-produced plasmas of hydrogen and deuterium has shown an isotope effect in the red-side region of the generated second harmonic light. This isotope shift is explained by the parametric instability at the cutoff (resonance) region using frequency-and phase-matching conditions of the waves.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.523-532
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• 1999

This study is aimed to obtain fundamental knowledge of pulse laser welding phenomena the authors investigated the structure and composition of evaporated particles of Al alloys in air and in the Ar atmosphere during pulsed laser welding. The ultra-fine particles of 5 to 100nm diameter in a globular or irregular shape were formed in laser-induced plasma and the main structure was $MgAl_2O_4$ The composition of particles was ifferent depending on the power density of a laser beam; namely under the low power density conditions magnesium was predominant in the parti-cles while aluminium content increased with an increase in the power density. These results were attributed to evaporation phenomena of metals with different boiling points and latent heats of vaporization. On the other hand the number density of laser-induced plasma species was obtained by Saha's equation. it was confirmed that the number density depends upon the plasma tempera-ture and total pressures.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.6
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• pp.479-487
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• 2020

A new double-pulse laser system that combines Raman and laser induced plasma spectroscopy (LIPS) in a single unit is proposed. The study attempts to enhance the laser induced plasma signals while simultaneously extracting the desired molecular signals from Raman spectroscopy. In low pressure conditions such as the lunar atmosphere, the measuring of plasma emission is hard because of the low electron density and short persistence time causing a rapid plasma expansion. Furthermore, in the integration of the detecting system aimed at space exploration, the minimization of laser system is important in terms of the payload mass. Simultaneous molecular and atomic detection that gave highly resolved spectral data at pressure below 0.07 torr is demonstrated amongst eight rock samples test. The plasma stacking produced from the double-pulse laser enhanced the signal intensity of calcium and oxygen lines in calcite matrix by twofold, compared to a conventional LIPS.

• Journal of Welding and Joining
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• v.9 no.1
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• pp.23-31
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• 1991

Laser beam weldability of zircaloy-4was investigated using a pulsed Nd: YAG laser of 200W average power. Mechanical properties of laser and GTA bead-on-plate welded zircaloy-4 test specimens were compared. The influence of plasma generated during laser welding was analyzed and optimum laser welding parameters were investigated.