• 한국광학회:학술대회논문집
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• 한국광학회 2006년도 하계학술발표회 논문집
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• pp.123-124
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• 2006

• 한국항공우주학회지
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• 제46권6호
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• pp.519-526
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• 2018

우주 자원을 분석하기 위해서는 지구로 가져와야 한다는 단점이 있었다. 하지만, 레이저 유도 분해 분광법(Laser-induced breakdown spectroscopy, LIBS)고 라만 분광법(Raman spectroscopy)을 활용한다면 우주 광물의 실시간 정성 정량적으로 분석이 가능하다. 레이저 유도 분해 분광법은 높은 에너지의 레이저를 물질 표면에 집중시켜 플라즈마를 생성한후, 방출되는 빛을 분광기를 통해 획득하여 원자 구성을 분석하는 분광법이다. 라만 분광법은 레이저를 물질 표면에 조사시켜 산란되는 빛을 측정하여 분자구조를 분석하는 분광법이다. 이 두 가지 분광법은 각각 미지의 광물의 원자 분자를 분석하는 상호보완적인 분광법으로 우주탑재체로서 효율적인 장점을 가지고 있다. 본 연구에서는 주성분 분석법(Principal Component Analysis, PCA)을 활용하여 광물을 정성적으로 분석했다. 또한, 두 가지 광물을 혼합한 시료를 제작하여 구성 성분 비율에 따른 신호 세기로부터 물질의 구성 비율을 예측하는 정량분석을 시행하였다.

• Rapid Communication in Photoscience
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• 제4권3호
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• pp.54-58
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• 2015

Under the condition of femtosecond impulsive nonlinear optical irradiation, the bright and narrowed blue emission of silicon nanocrystal was observed. This synthetic method produced very small (~ 4 nm) oxide-capped silicon nanocrystal having probably ultra small emitting core (~ 1 nm) inferred from luminescence. By controlling the stirring condition, very high efficiencies of luminescence ( 4 fold higher) were obtained compared with the other conventional femtosecond laser fragmentation methods, which was attributed to the differences in hydration shell structure during the femtosecond laser induced irreversible phase transition reaction. When we properly adjusted the irradiation times of the white light continuum and stirring condition, very homogeneous luminescent silicon nanocrystal bands having relatively sharp lineshape were obtained, which can be attributable to the luminescent core site isolated and free from the surface defects.

• Transactions on Electrical and Electronic Materials
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• 제10권2호
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• pp.53-57
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• 2009

In this paper we develop a method to observe faults in semiconductor devices and transmission lines by calculating the variation of the reflection function in a dielectric microstrip line that has an open-ended termination containing an optically induced plasma region. It is analyzed with the assumption that the plasma is distributed homogeneously in laser illumination. With the non linear material of degradation, the concentration of the carrier in the part of the material has changed. Since the input wave has produced the phenomenon of reflection, the input signal to the open-ended microstrip lines can be observed on reflection to identify the location of the fault. The characteristic impedances resulting from the presence of plasma are evaluated by the transmission line model. The variation of the reflection wave in the microwave system has been calculated by using an equivalent circuit model. The transient response has been also evaluated theoretically for changing the phase of the variation in the reflection. The variation of characteristic response in differentially localized has been also evaluated analytically.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.179-179
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• 2012

Low pressure radio-frequency glow discharges are investigated using theoretical modeling and various experimental diagnostic methods. In the calculations, global models and transformer models are developed to understand the chemical kinetics as well as the electrical properties such as the effective collision frequency, the heating mechanism and the power transferred to the plasma electrons. In addition, Boltzmann equation solver is used to compensate the effect of the electron energy distribution function (EEDF) shape in the global model, and the general expression of energy balance for non-Maxwellian electrons is developed. In the experiments, a number of traditional plasma diagnostic methods are used to compare with calculated results such as Langmuir probe, optical emission spectroscopy (OES), optical absorption spectroscopy (OAS) and two-photon absorption laser-induced fluorescence (TALIF). These theoretical and experimental methods are applied to understand several interesting phenomena in low pressure ICP discharges. The chemical and physical properties of low pressure ICP discharges are described and the applications of these methods are discussed.

• 분석과학
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• 제26권4호
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• pp.235-244
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• 2013

할로겐족 원소들의 강한 원자 방출선들은 진공자외선 영역에 존재하여, 공기 중에서 레이저 펄스를 시료에 집속하여 플라즈마 방출 스펙트럼을 얻어 원소 분석을 수행하기 매우 어렵다. 또한 근적외선 영역에 할로겐족 원소들의 들뜬 전자 상태들 사이의 전이에 의한 원자 방출선들이 존재하는데, 이들은 스타크 효과에 의한 선폭 넓어짐 현상이 매우 커서, 공기 중에서 원소 분석에 충분한 신호 대 잡음비를 얻기 어렵다. 헬륨 가스 플로우를 이용하여 근적외선 영역의 할로겐족 원소들의 원자 방출선들은 레이저유도 플라즈마로부터 관측하였다. 특히, 804.374 nm와 905.833 nm의 아이오딘 원자 방출선들은 레이저유도 플라즈마에서 처음으로 관찰된 것이다. 헬륨 분위기에서 스타크 효과에 의한 선폭 넓어짐 현상과 연속 배경복사의 세기는 현저히 억제되었다. 헬륨 가스 플로우의 유량에 따른 원자 방출선의 세기, 플라즈마 온도, 전자 밀도의 변화를 조사하였다. 이 방법을 이용하여 고무의 난연제 성분에 포함된 염소와 불소를 레이저유도 플라즈마 분광법을 이용하여 검출하였다. 마지막으로 레이저유도 플라즈마 분광법을 이용하여 할로젠 원소들을 검출하는데 헬륨 가스 소모량을 줄일 수 있는 가스 펄스 젯 장치를 제안한다.

• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.636-644
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• 2006

Recently, there were some successful examples that the laser welding was introduced into production line. However, the spread of laser welding is not sufficient in many industries. There are several reasons why it is difficult to penetrate the laser welding into production lines. Because it is different from reflection, absorption and permeation of laser beam according to material and surface condition. Moreover, there are significant problems in processing such as absorption and scattering of beam by the induced plasma or plume. Therefore, understanding of mechanism on formation of weld defect in laser welding of the laminated core for motor is very important. In this paper, it was analyzed in terms of materials which was source of defect in laser welding and conventional arc welding. As a results of analysis, insulation coating film of the laminated core was judged to main factor of weld defect. it could be well aware as tracing carbon volume, and it was deduced that weld defect by insulation coating film was caused by difference of mechanism between the two heat sources.

• Journal of the Optical Society of Korea
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• 제17권6호
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• pp.548-558
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• 2013

In this work, laser induced breakdown spectroscopy (LIBS) is used to investigate soil samples collected from different desert areas of Riyadh city in Saudi Arabia. Both qualitative analysis and plasma parameters are studied via the observed LIBS spectra. These experiments have been done using a Spectrolaser-7000 system with 50 mJ fundamental wavelength of Nd:YAG laser and detection delay time of 1 microsecond. Many spectral lines are highly resolved for many elements like Al, Fe, Mg, Si, Mn, Na, Ca and K. The electron temperatures Te and electron densities Ne, for the constituent of generated LIBS plasma, are determined for all the collected samples. It is found that both Te and Ne vary from one desert area to other. This variation is due to the change of the elemental concentration in different desert areas that affects the sample's matrices. Time dependent measurements have also been performed on the soil samples. While the signal-to-base ratio (SBR) reached its optimal value at 1 microsecond, the plasma parameters Ne and Te reach values of $4{\times}10^{17}cm^{-3}$ and 9235 K, respectively, at 2.5 microsecond. The later indicate that the plasma cooling processes are slow in comparison to the previously observed results for metallic samples. The observed results show also that in the future it is possible to enhance the exploitation of LIBS in the remote on-line environmental monitoring application, by following up only the values of Ne and Te for one element of the soil desert sample using an optical fiber probe.

• Current Optics and Photonics
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• 제1권4호
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• pp.402-411
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• 2017

Combined LIBS-Raman spectroscopy has been widely studied, due to its complementary capabilities as an elemental analyzer that can acquire signals of atoms, ions, and molecules. In this study, the classification of polymorphs was performed by laser-induced breakdown spectroscopy (LIBS) to overcome the limitation in molecular analysis; the results were verified by Raman spectroscopy. LIBS signals of the $CaCO_3$ polymorphs calcite and aragonite, and $CaSO_4{\cdot}2H_2O$ (gypsum) and $CaSO_4$ (anhydrite), were acquired using a Nd:YAG laser (532 nm, 6 ns). While the molecular study was performed using Raman spectroscopy, LIBS could also provide sufficient key data for classifying samples containing different molecular densities and structures, using the peculiar signal ratio of $5s{\rightarrow}4p$ for the orbital transition of two polymorphs that contain Ca. The basic principle was analyzed by electronic motion in plasma and electronic transition in atoms or ions. The key factors for the classification of polymorphs were the different electron quantities in the unit-cell volume of each sample, and the selection rule in electric-dipole transitions. The present work has extended the capabilities of LIBS in molecular analysis, as well as in atomic and ionic analysis.

• 해양환경안전학회지
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• 제3권2호
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• pp.23-31
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• 1997

The results of high speed photography, acoustic emission detection and plasma UV radiation intensity measurement during CO2 laser welding of stainless steel 304 are presented. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of a high speed melt flow which originated from the part of weld pool and flowed along the sides wall of keyhole was confirmed by the slag motion on the weld pool. the characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal acoustic emission (AE) and light emission (LE) spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. (The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation.) The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10mm/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.