• 대한기계학회논문집B
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• 제25권8호
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• pp.1140-1147
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the microscale regime are essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing application, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse(λ=248nm, FWHM=24ns) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of 0.1㎛ and 1m/s, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• Journal of Welding and Joining
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• 제33권5호
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• pp.53-60
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• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.199-199
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• 2009

Recently, polymeric microlens arrays have become important elements in many applications. Microlens arrays have been used to enhance luminance efficiency and luminance power efficiency of light-emitting diodes (LEDs) and organic LEDs. Many processes for fabrication of microlens array are studied. Though the MLA has been fabricated by electroformed mold, LIGA process and reflow method, these methods were required masks, multiple process steps and post processing. In this paper, we proposed rapid and direct UV laser direct fabrication process using colorless liquid photopolymer, NOA60 for polarization activated microlens. The microlens arrays are formed on the NOA60 on glass, after the focused laser energy was irradiated to the material. The diameter of MLA was varied from 42 to 88 ${\mu}m$, and the height from 0.9 to 1.6 ${\mu}m$. The MLA fabricated using NOA60 shows more then 85% transmittance as well as good hardness for optical module.

• Journal of Welding and Joining
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• 제34권1호
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• pp.75-81
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• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• 한국응용과학기술학회지
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• 제23권4호
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• pp.340-346
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• 2006

The influences of fluorescence, scattering, and flocculation in turbid material by light scattering were interpreted for the scattered fluorescence intensity and wavelength, it has been studied the molecular properties by the spectroscopy of laser induced fluorescence (LIF). The effects of optical properties in scattering media have been found by the optical $parameters({\mu}_s,\;{\mu}_a,\;{\mu}_t)$. Flocculation is an important step in many solid-liquid separation processes and is widely used. When two particles approach each other, interactions of several colloid particles can come into play which may have major effect on the flocculation and LIF process, The value of scattering coefficient ${\mu}_s$ is large by means of the increasing particles of scatterer it has been found that the slope decays exponentially as a function of distance from laser source to detector. It may also aid in designing the best model for oil chemistry, biopharmaceutical products, laser medicine and application of medical engineering on LIF and coagulation in particle transport mode.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1120-1125
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• 2004

Welding characteristics of STS304 stainless steel and Inconel 600 using a continuous wave Nd:YAG laser are experimentally investigated. Alloy 600 being used in steam generator tubing of pressurized water reactor(PWR) exposed to some corrosion environment, stress corrosion cracking can occur on this material. Presented here are the results from a series of experiments in which dissimilar metal welds were made using the gas tungsten arc welding process with pure argon shielding gas. But It is well known that solidification cracking susceptibility of austenitic alloys depends on the solidification temperature range and amount/distribution of solute rich liquid that exists at the terminal stages of solidification. An experimental study was conducted to determine effects of welding parameters and to optimize those parameters that have the most influence on eliminating or reducing the extent welding zone formation at dissimilar metal welds.

• 한국결정성장학회지
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• 제30권2호
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• pp.73-77
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• 2020

본 연구에서는 차세대 자동차 레이저 헤드램프 적용을 위하여 분무건조법을 통하여 가넷 구조를 갖는 구형의 YAG : Ce 형광체를 합성하였으며 이를 기반으로 형광체 세라믹을 제조하고 광학적 특성을 분석하였다. 분무건조법 기반으로 합성된 구형의 YAG : Ce 형광체를 이용한 형광체 세라믹의 두께를 100 ㎛, 150 ㎛, 200 ㎛로 조절하여 두께에 따른 광변환 효율, 열 소광, 휘도 및 색온도의 광학적 특성을 비교하였다. 연구 결과, 양자효율 및 광속 값은 두께가 150 ㎛ 일 때, 가장 높게 나타났다. 본 연구 결과는 기존의 액상법을 기반으로 한 YAG : Ce 나노 형광체 제조의 고 비용, 저 수율 등의 문제점을 개선한 방법으로 향 후, 형광체 세라믹 제조에 큰 역할을 할 수 있을 것이라 기대된다.

• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3547-3552
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• 2014

Laser Raman spectroscopy is one of the most powerful technologies for standoff detection of hazardous materials including explosives. Supported by recent development of laser and sensitive ICCD camera, the technology can identify trace amount of unknown substances in a distance. Using this concept, we built a standoff detection system, in which nanosecond pulse laser and nanosecond gating ICCD technique were delicately devised to avoid the large background noise which suppressed weak Raman signals from the target sample. In standoff detection of explosives which have large kill radius, one of the most important technical issues is the detection distance from the target. Hence, we focused to increase the detection distance up to 54 m by careful optimization of optics and laser settings. The Raman spectra of hazardous materials observed at the distance of 54 m were fully identifiable. We succeeded to detect and identify eleven hazardous materials of liquid or solid particles, which were either explosives or chemical substances used frequently in chemical plants. We also performed experiments to establish the limit of detection (LOD) of HMX at 10 m, which was estimated to be 6 mg.

• Journal of Dairy Science and Biotechnology
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• 제25권2호
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• pp.5-10
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• 2007

Ultrasonication was employed to prepare solid lipid nanoparticles (SLN) for smart probiotic nanoparticles as a nanofood. The model probiotic material, lactocin from Lactobacillus plantarum (CBT-LP2), was incorporated into SLN. The CBT-LP2 loaded SLN (CBT-LP2-SLN) were spherical in the photograph of scanning electron microscope (SEM). The particle size measured by laser diffraction (LD) was found to be $97.3{\pm}8.2nm$. Zeta potential analyzer suggested the zeta potential of LP-SLN was $-29.36{\pm}3.68$ mV in distilled water. The entrapment efficiency (EE%) was determined with the sephadex gel chromatogram and high-performance liquid chromatogram (HPLC), and up to 90.59% of nanofood was incorporated. Stability evaluation showed relatively long-term stability with only slight particle growth (P>0.05) after storage at room temperature for 4 weeks. Therefore, ultrasonication is demonstrated to be a simple, available and effective method to prepare high quality SLN loaded probiotic material.

• 한국광학회지
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• 제10권4호
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• pp.318-322
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• 1999

액체 레이저의 매질 개발을 목적으로 $Nd^{3+}$ 주위에 저진동 모드의 결합으로 배위자를 형성하는 $Nd(HFA-D)_3$ 착물에 있어서의 $Nd^{3+}$ 이온의 발광특성은 유기용매의 종류에 의존하며, 강한 배위능력을 지니고 있는 용매일수록 발광특성이 우수한 결과로부터 액체 레이저 매질의 개발 시 유기용매로서는 $DMSO-d_6$가 유력한 후보임을 제시하였다. $DMSO-d_6$ 용매로 사용한 $Nd(HFA-D)_3$ 착물의 경우, 파장 585nm($^4F_{3/2}$)에 있어서의 흡수단면적은 $0.92{\times}10^{-20}\textrm{cm}^2$, 발광강도는 1.0$\mu\textrm{m}$대($^4F_{3/2}\Rightarrow ^4I_{11/2}$, Peak파장 : 1062nm)에서 가장 강하였으며, 발광스펙트럼의 반치폭 (FHWM)은 31nm, 발광수명은 약 12.0mus, 유도방출 단면적은 $3.89{\times}10_{-20}\textrm{cm}^2$ 였다.