• Journal of the Korean Institute of Gas
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• 제27권1호
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• pp.70-77
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• 2023

Air environment regulations have been strengthened due to increasing air pollutant emissions, the target of reducing emissions has increased and interest in gas measurement methods is also increasing. The sampling method is mainly used, but due to the spatial and temporal measurement limitations, the laser absorption spectroscopy which is a real-time and in-situ method is in the spotlight. In this study, we studied the wavelength modulation spectroscopy and described the calibration-free algorithm. The developed algorithm was modified to reflect 46 multi-absorption lines and was applied to light absorption signal analysis in visible and mid-infrared regions. In addition, the difference between the modulation parameters of laser was analyzed. As a result of reviewing the performance through O₂ and NO gas measurement experiments of various concentration conditions, the linearity was R²_O2=0.99999 and R²_NO=0.99967.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제6권1호
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• pp.58-63
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• 2005

PTFE (polytetrafluoroethylene) thin films were prepared from the pellets of the graphite doped PTFE via pulsed laser ablation with 1064 nm Nd:YAG laser. The graphite powder converts the absorbed photon energy into thermal energy which is transmitted to nearby PTFE. The PTFE is decomposed by thermal process. The deposited films were transparent and crystalline. SEM (scanning electron microscopy) and AFM (atomic force microscopy) analyses indicated that the film surface morphology changed to fibrous structure with increasing thickness. The fluorine to carbon ratios of the film were 1.7 and molecular axis was parallel with (100) Si-wafer substrate. These results obtained by XPS (X-ray photoelectron spectroscopy), FTIR (fourier transform infrared spectroscopy) and XRD (X-ray diffraction).

• Journal of the Korean Society for Nondestructive Testing
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• 제28권2호
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• pp.119-124
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• 2008

In recent years, gradually increasing interest has been directed to the use of terahertz technology in nondestructive testing and non-invasive measurements, and terahertz time domain spectroscopy (THz-TDS) has become a key technology in such applications. This paper deals with the terahertz pulse generation from cadmium telluride via optical rectification process of femto-second infrared laser pulses. The measured terahertz spectrum is compared with the result of model calculation based on space-time domain nonlinear Maxwell equations for coherent frequency mixing process. The propagation process of terahertz and infra-red pulses in the material as well as the surface interference and free space diffraction effects are also considered. The experimental results are in good agreements with the calculated spectrum.

• Korean Journal of Optics and Photonics
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• 제13권2호
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• pp.123-127
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• 2002

We have measured the wavelengths of the absorption lines of the $^{13}$ C$_2$H$_2$molecule by using a wavelength meter calibrated against the national optical frequency standard (iodine Stabilized He-Ne Laser, KRISS-R701) in the visible wavelength region. To measure the absolute wavelengths of the absorption lines, the frequency of the laser has been stabilized in the peaks and the sides of the absorption lines of $^{13}$ C$_2$H$_2$. Also, we have proposed the development of a frequency standard source of ITU-T grid using stabilization in the sides of the absorption lines of $^{13}$ C$_2$H$_2$.

• Proceedings of the Optical Society of Korea Conference
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.236-237
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• 2000

용액인상법에 의하여 Cr$^{3+}$ 이온이 0.1-0.2% 주입된 Alexandrite (Cr$^{3+}$ :BeAl$_2$O$_4$) 단결정을 성장하고, 성장한 단결정을 이용하여 레이저 소자를 제조하였다. 고품질의 단결정을 성장할 수 있는 결정성장조건을 규명하고, Cr$^{3+}$ 이온의 유효편석 계수를 계산하였으며, 결정 결함 및 분광 물성을 조사하였다. 결정성장 실험 결과, 유속 3 1/min의 질소분위기, 이리듐 도가니 및 <001>방위의 Alexandrite 단결정을 종자결정으로 사용하여 결정을 성장하는 경우 최적의 결정성장 조건은 인상속도 0.5-1.0 mm/hr와 회전속도 20-25 rpm이었다. 육성된 결정은 (100)면이 넓게 발달되었으며, (120)과 (010)면이 측면에 발달되는 판상의 직팔각기둥의 형태로 성장되었다. 결정결함으로써 parasite crystal의 형성과 경계면의 균열, striation, inclusion 등이 검출되었다. Alexandrite 단결정 내에 분포하는 Cr$^{3+}$ 이온의 유효편석계수 k$_{eff}$는 2.8로 계산되었다. 분광물성으로써 실온에서의 $^4$A$_2$$\longrightarrow$$^4$T$_2$(689.6-489.3 nm), $^4$A$_2$$\longrightarrow$$^4$T$_1$(489.3-311.33m) 천이에 의한 흡수를 확인하고, $^4$T$_2$$\longrightarrow$$^4$A$_2$(650-800 nm), $^2$E$\longrightarrow$$^4$A$_2$에 의한 nophonon line R$_1$, R$_2$(680.4, 678.5 nm) 및 $^2$T$_1$$\longrightarrow$$^4$A$_2$(655.7, 649.3, 645.2 nm)의 형광방출 스펙트럼을 얻었으며, 형광수명은 0.264 ms로 조사되었다. 제조된 레이저 발진봉은 직경 6.3 m, 길이 45 nm이었다.

• Journal of the Korean Chemical Society
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• 제34권5호
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• pp.404-412
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• 1990

The time resolved electron spin resonance spectroscopy are used to two measurement methods of chemically induced dynamic electron polarization (CIDEP) and absorption ESR. The spectra of the semiquinone radical anion were successively detected in the laser flash photolysis of anthraquinone in the mixtures of 2-propanol and triethylamine. The semiquinone radical anion was fairly stable and its cw ESR could be observed. The rate constant (T1$^{-1}$) of the spin-depolarization of polarized semiquinone radical anion was 2.6 ${\times}\;1-^5$ sec$^{-1}$ and the decay of the radical anion was the first order with the rate constant (K$_1}$) of 300.0 sec$^{-1}$. The intensity of CIDEP spectra increased with the increasing the microwave power, but the Torrey wiggles appeared following with decay curves.

• Economic and Environmental Geology
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• 제46권6호
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• pp.495-508
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• 2013

Recently, stable isotopes (${\delta}^{18}O$ and ${\delta}D$) of water are increasingly analyzed using laser-based technologies. These methods have advantages over Isotope Ratio Mass Spectrometry (IRMS) in that they can be used for in-situ measurements and require much less maintenance and preparation work. Two types of laser-based methods are currently available, which have different analytical principles; OA-ICOS (off-axis integrated cavity output spectroscopy) and WS-CRDS (wavelength-scanned cavity ring-down spectroscopy). In the WS-CRDS instrument, water is vaporized at controlled environment and transferred to an optical cavity by nitrogen carrier gas, and stable isotopic compositions of water vapor are measured using the degree of absorbance of specific wavelengths and the ratios of attenuation time of the laser intensity with the sensitivity of ppb to tens of ppt level. In this study, we introduce the principle of the WS-CRDS technology and the performance results including stability and comparisons with Isotope Ratio Mass Spectrometry (IRMS) and suggest possible applications of various topics in isotope hydrology.

• Proceedings of the Optical Society of Korea Conference
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• 한국광학회 2003년도 제14회 정기총회 및 03년 동계학술발표회
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• pp.200-201
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• 2003

여러 가지 원소의 동위원소 성분 분석은 생물학, 화학, 환경학, 연대학, 기후학 연구에 있어서 중요한 정보를 제공하는 유용한 수단이다. 그 중에서도 수소, 산소, 그리고 탄소 동위원소 성분비의 정밀한 측정은 지구의 기후 변화 연구 등에 필수적인 수단이며, 가깝게는 식음료의 원산지 및 품질 확인에 이르기까지 다양하게 응용되고 있다 대표적으로 활용되고 있는 예를 보면 다음과 같다. 1. Authenticity Control and Detection of Adulteration： 쥬스류에 첨가제를 사용했는지의 여부를 확인할 수 있고, 포도주의 진품 여부를 확인할 수 있으며 원산지 확인도 가능하다. (중략)

• Journal of the Korean Institute of Gas
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• 제24권5호
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• pp.29-38
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• 2020

It is practically difficult to accurately measure the temperature and concentration of a large combustion systems at industrial sites in real time. Temperature measurement using thermocouple, which are mainly used, is a point-measuring method that is less accurate and less reliable to analyze the wide area range of inner combustion system, and has limitations to internal accessibility. In terms of concentration analysis, most measurement methods use sampling method, which are limited by the difficulty of real-time measurement. As a way to overcome these limitations, laser-based measurement methods have been developed continuously. Laser-based measurement are line-average measurement methods with high representation and precision, which are beneficial for the application of large combustion systems. In this study the temperature and concentration were measured in real time by water vapor and oxygen generated during combustion using Tunable Diode Laser Absorption Spectroscopy (TDLAS). The results showed that the average temperature inside the combustion system was 1330℃ and the mean oxygen concentration was 3.3 %, which showed similar tendency with plant monitoring data.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• 제9권4호
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• pp.207-217
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• 2011

In this study the complex formation reactions between uranium(VI) and 2,6-dihydroxybenzoate (DHB) as a model ligand of humic acid were investigated by using UV-Vis spectrophotometry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The analysis of the spectrophotometric data, i.e., absorbance changes at the characteristic charge-transfer bands of the U(VI)-DHB complex, indicates that both 1:1 and 1:2 (U(VI):DHB) complexes occur as a result of dual equilibria and their distribution varies in a pH-dependent manner. The stepwise stability constants determined (log $K_1$ and log $K_2$) are $12.4{\pm}0.1$ and $11.4{\pm}0.1$. Further, the TRLFS study shows that DHB plays a role as a fluorescence quencher of U(VI) species. The presence of both a dynamic and static quenching process was identified for all U(VI) species examined, i.e., ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$. The fluorescence intensity and lifetimes of each species were measured from the time-resolved spectra at various ligand concentrations, and then analyzed based on Stern-Volmer equations. The static quenching constants (log $K_s$) obtained are $4.2{\pm}0.1$, $4.3{\pm}0.1$, and $4.34{\pm}0.08$ for ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$, respectively. The results of Stern-Volmer analysis suggest that both mono- and bi-dentate U(VI)-DHB complexes serve as groundstate complexes inducing static quenching.