• 한국광학회지
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• 제10권3호
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• pp.226-232
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• 1999

연속 발진 Nd: YAG 레이저를 펌핑 광원으로 하여 보다 조밀하고 견고하며, 안정된 연속 발진 파장 가변 Cr4+ : YAG 레이저를 개발하여 레이저 출력 특성, 파장 가변성 및 발진 레이저 선폭 등을 조사하였다. 공진기 구조는 공진기 안정 조건을 계산하여 비점수차가 보상된 Z 자형 접힘 공진기를 구성하였다. 공진기 출력 거울의 투과율이 1%일 때, 결정의 온도를 2$0^{\circ}C$로 유지하며 6W로 펌핑하였을 경우, 중심 파장이 1.45$\mu\textrm{m}$에서 최대 400 mW의 평균 출력을 갖는 매우 안정된 연속 발진 Cr4+ : YAG 레이저를 얻을 수 있었으며, 출력 기울기 효율은 8%였다. 또한 공진기 내에 복굴절 필터를 삽입하여 1.399 $\mu\textrm{m}$에서 1.532 $\mu\textrm{m}$까지의 파장 가변 영역을 얻었고, 1.4903 $\mu\textrm{m}$에서 최대 340 mW의 평균 출력을 얻을 수 있었으며, 이때의 레이저 발진 선폭은 0.21 $\mu\textrm{m}$였다.

• 전기학회논문지
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• 제67권6호
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• pp.789-793
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• 2018

All transparent metal oxide photoelectric device based on $V_2O_5$ was fabricated with structure of $V_2O_5/ZnO/ITO$ by magnetron sputtering system. $V_2O_5$ was deposited by reactive sputtering system with 4 inch vanadium target (purity 99.99%). In order to achieve p-n junction, p-type $V_2O_5$ was deposited onto the n-type ZnO layer. The ITO (indium tin oxide) was applied as the electron transporting layer for effective collection of the photo-induced electrons. Electrical and optical properties were analyzed. The Mott-Schottky analysis was applied to investigate the energy band diagram through the metal oxide layers. The $V_2O_5/ZnO/ITO$ photoelectric device has a rectifying ratio of 99.25 and photoresponse ratios of 1.6, 4.88 and 2.68 under different wavelength light illumination of 455 nm, 560 nm and 740 nm. Superior optical properties were realized with the high transmittance of average 70 % for visible light range. Transparent $V_2O_5$ layer absorbs the short wavelength light efficiently while passing the visible light. This research may provide a route for all-transparent photoelectric devices based on the adoption of the emerging p-type $V_2O_5$ metal oxide layer.

• 천문학회보
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• 제46권2호
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• pp.38.1-38.1
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• 2021

Dust polarization depends on the physical and mechanical properties of dust, as well as the properties of local environments. To understand how dust polarization varies with grain mechanical properties and the local environment, in this paper, we model the wavelength-dependence polarization of starlight and polarized dust emission by aligned grains by simultaneously taking into account grain alignment and rotational disruption by radiative torques (RATs). We explore a wide range of the local radiation field and grain mechanical properties characterized by tensile strength. We find that the maximum polarization and the peak wavelength shift to shorter wavelengths as the radiation strength U increases due to the enhanced alignment of small grains. Grain rotational disruption by RATs tends to decrease the optical-near infrared polarization but increases the ultraviolet polarization of starlight due to the conversion of large grains into smaller ones. In particular, we find that the submillimeter (submm) polarization degree at 850㎛(P850) does not increase monotonically with the radiation strength or grain temperature (Td), but it depends on the tensile strength of grain materials. Our physical model of dust polarization can be tested with observations toward star-forming regions or molecular clouds irradiated by a nearby star, which have higher radiation intensity than the average interstellar radiation field. Finally, we compare our predictions of the P850-Td relationship with Planck data and find that the observed decrease of P850 with Td can be explained when grain disruption by RATs is accounted for, suggesting that interstellar grains unlikely to have a compact structure but perhaps a composite one. The variation of the submm polarization with U (or Td)can provide a valuable constraint on the internal structures of cosmic dust

• 분석과학
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• 제20권2호
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• pp.170-175
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• 2007

올리브유중 벤조피렌을 분석하기 위하여 고속액체크로마토그래피/형광검출기를 이용하였다. 시료의 지방성분을 헥산으로 제거한 후 N,N-DMF 수용액을 다시 헥산으로 추출하여 후로리실 SPE 카트리지로 정제한 후 기기분석하였다. 이동상으로는 아세토니트릴과 물의 혼합용액(8:2)을 사용하였으며 형광검출기의 여기파장은 294 nm이었고 형광파장은 404 nm이었다. 평균 회수율은 95%이었으며, 정량한계는 $0.9{\mu}g/kg$이었다. 대상 식품인 올리브유 중 벤조피렌의 검출수준은 불검출~$1.9\mu}g/kg$이었으나, 식품공전의 기준인 올리브유중 벤조피렌의 최대수준 $2.0{\mu}g/kg$이하이었다.

• 한국입자에어로졸학회지
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• 제6권2호
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• pp.91-103
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• 2010

Size-segregated number concentration and scattering coefficient of urban aerosols were measured using an SMPS (scanning mobility particle sizer) and a nephelometer, respectively in Seoul, Korea, during the winter season of 2003. The average number concentrations of ultrafine particles (20~100 nm) and accumulation mode particles (100~600 nm) were $2,170\;particles\;cm^{-3}$ and $1,521\;particles\;cm^{-3}$, respectively. The scattering coefficient at the wavelength of 550 nm ranged from $62.6Mm^{-1}$ to $330.1Mm^{-1}$ and average value was $163.4Mm^{-1}$. The peak concentrations of ultrafine particles and accumulation mode particles were simultaneously recorded between 6:00 and 9:00 A.M., indicating the effect of vehicle emissions which are major air pollution sources in the urban atmosphere. On average, the number concentration of ultrafine particles was 1.4 times higher than that of accumulation mode particles, although it was a little higher during the morning peak time. The variation of aerosol scattering coefficient was in good agreement with that of accumulation mode particle number concentration rather than that of ultrafine particle number concentration.g coefficient was in good agreement with that of accumulation mode particle number concentration rather than that of ultrafine particle number concentration.

• Current Optics and Photonics
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• 제5권2호
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• pp.186-190
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• 2021

In this study, a compact, picosecond, mid-infrared 3.8 ㎛ MgO:PPLN optical parametric oscillator (OPO) laser output with high peak power is realized using a master oscillator power amplifier (MOPA) 1 ㎛ solid-state laser seeded by a picosecond fiber laser as the pump source. The pump source was a 50 MHz and 10 ps fiber seed source. After AOM pulse selection and two-stage solid-state amplification, a 1,064 nm laser output with a repetition frequency of 1-2 MHz, pulse width of 9.5 ps, and a maximum average power of 20 W was achieved. Furthermore, a compact short cavity with a unsynchronized pump is adopted through the design of an OPO cavity structure. When the injection pump power was 15 W and the repetition frequency was 1 MHz, the average output power of idler light was 1.19 W, and the corresponding peak power was 119 kW. The optical conversion efficiency was 7.93%. When the repetition frequency was increased to 2 MHz, the average output power of idler light was 1.63 W, the corresponding peak power was 81.5 kW, and the optical conversion efficiency was 10.87%. At the same time, the output wavelength was measured at 3,806 nm, and the beam quality was MX2 = 3.21 and MY2 = 3.34.

• 한국해양공학회지
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• 제36권1호
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• pp.32-40
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• 2022

Underwater optical images face various limitations that degrade the image quality compared with optical images taken in our atmosphere. Attenuation according to the wavelength of light and reflection by very small floating objects cause low contrast, blurry clarity, and color degradation in underwater images. We constructed an image data of the Korean sea and enhanced it by learning the characteristics of underwater images using the deep learning techniques of CycleGAN (cycle-consistent adversarial network), UGAN (underwater GAN), FUnIE-GAN (fast underwater image enhancement GAN). In addition, the underwater optical image was enhanced using the image processing technique of Image Fusion. For a quantitative performance comparison, UIQM (underwater image quality measure), which evaluates the performance of the enhancement in terms of colorfulness, sharpness, and contrast, and UCIQE (underwater color image quality evaluation), which evaluates the performance in terms of chroma, luminance, and saturation were calculated. For 100 underwater images taken in Korean seas, the average UIQMs of CycleGAN, UGAN, and FUnIE-GAN were 3.91, 3.42, and 2.66, respectively, and the average UCIQEs were measured to be 29.9, 26.77, and 22.88, respectively. The average UIQM and UCIQE of Image Fusion were 3.63 and 23.59, respectively. CycleGAN and UGAN qualitatively and quantitatively improved the image quality in various underwater environments, and FUnIE-GAN had performance differences depending on the underwater environment. Image Fusion showed good performance in terms of color correction and sharpness enhancement. It is expected that this method can be used for monitoring underwater works and the autonomous operation of unmanned vehicles by improving the visibility of underwater situations more accurately.

• 대한환경공학회지
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• 제28권2호
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• pp.223-228
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• 2006

본 연구에서는 fluorescence derivatization 기법과 HPLC를 이용하여 수중에 nanograms per liter로 존재하는 극미량 N-nitrosodimethylamine(NDMA)를 분석하고자 하였다. 이를 위해 먼저 다양한 조건 하에서의 fluorescence intensity를 측정함으로써 derivatization 기법을 최적화하였는데, fluorescence detector의 excitation/emission wavelength는 340 nm(excitation)과 530 nm(emission)에서, denitrosation 후 용액의 pH는 9-12의 범위에서, 그리고 dansyl chloride의 농도는 330-500 mg/L 범위에서, 최대 fluorescence intensity를 보여주였다. 용매추출을 통한 수질 시료의 분석에서, 표준농도와 검출농도의 차이는, 저농도(10-200 ng/L) 범위에서 12-162%, 고농도(100-1000 ng/L) 범위에서 6-23%를 보여, 저농도 범위에서 더 많은 차이가 나는 것으로 나타났으나, 두 농도 범위 모두 표준농도와 검출농도의 평균 대비율이 1에 매우 근접해 있어, 수십에서 수백 nanograms NDMA per liter의 분석이 가능함을 보여주었다. 하수처리장 처리수에 주입한 NDMA의 분석에서도 다른 물질에 의한 간섭없이 정확한 농도 검출이 가능했는데, 이는 목적물질을 선별적으로 분석해내는 derivatization 과정에 의한 것으로 나타났다. HPLC와 fluorescence derivatization 기법을 이용한 NDMA의 분석은 상수 및 하수를 사용하는 다양한 실험 연구에서 NDMA를 분석하는 방법으로 효과적으로 사용될 수 있을 것이다.

• 천문학회보
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• 제43권1호
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• pp.34.2-35
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• 2018

Galaxy transition from star-forming to quiescent, accompanied with morphology transformation, is one of the key unresolved issues in extragalactic astronomy. Although several environmental mechanisms have been proposed, a deeper understanding of the impact of environment on galaxy transition still requires much exploration. My Ph.D. thesis focuses on which environmental mechanisms are primarily responsible for galaxy transition in different environments and looks at what happens during the transition phase using multi-wavelength photometric/spectroscopic data, from UV to mid-infrared (MIR), derived from several large surveys (GALEX, SDSS, and WISE) and our GMOS-North IFU observations. Our multi-wavelength approach provides new insights into the *late* stages of galaxy transition with a definition of the MIR green valley different from the optical green valley. I will present highlights from three areas in my thesis. First, through an in-depth study of environmental dependence of various properties of galaxies in a nearby supercluster A2199 (Lee et al. 2015), we found that the star formation of galaxies is quenched before the galaxies enter the MIR green valley, which is driven mainly by strangulation. Then, the morphological transformation from late- to early-type galaxies occurs in the MIR green valley. The main environmental mechanisms for the morphological transformation are galaxy-galaxy mergers and interactions that are likely to happen in high-density regions such as galaxy groups/clusters. After the transformation, early-type MIR green valley galaxies keep the memory of their last star formation for several Gyr until they move on to the next stage for completely quiescent galaxies. Second, compact groups (CGs) of galaxies are the most favorable environments for galaxy interactions. We studied MIR properties of galaxies in CGs and their environmental dependence (Lee et al. 2017), using a sample of 670 CGs identified using a friends-of-friends algorithms. We found that MIR [3.4]-[12] colors of CG galaxies are, on average, bluer than those of cluster galaxies. As CGs are located in denser regions, they tend to have larger early-type galaxy fractions and bluer MIR color galaxies. These trends can also be seen for neighboring galaxies around CGs. However, CG members always have larger early-type fractions and bluer MIR colors than their neighboring galaxies. These results suggest that galaxy evolution is faster in CGs than in other environments and that CGs are likely to be the best place for pre-processing. Third, post-starburst galaxies (PSBs) are an ideal laboratory to investigate the details of the transition phase. Their spectra reveal a phase of vigorous star formation activity, which is abruptly ended within the last 1 Gyr. Numerical simulations predict that the starburst, and thus the current A-type stellar population, should be localized within the galaxy's center (< kpc). Yet our GMOS IFU observations show otherwise; all five PSBs in our sample have Hdelta absorption line profiles that extend well beyond the central kpc. Most interestingly, we found a negative correlation between the Hdelta gradient slopes and the fractions of the stellar mass produced during the starburst, suggesting that stronger starbursts are more centrally-concentrated. I will discuss the results in relation with the origin of PSBs.

• 한국대기환경학회지
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• 제34권5호
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• pp.727-734
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• 2018

In this study, real-time absorption coefficients of carbonaceous species in $PM_{2.5}$ was observed using a dual-spot 7-wavelength Aethalometer between November 1, 2016 and December 31, 2017 at an urban site of Gwangju. In addition, 24-hr integrated $PM_{2.5}$ samples were simultaneously collected at the same site and analyzed for organic carbon and elemental carbon (OC and EC) using the thermal-optical transmittance protocol. A main objective of this study was to estimate mass absorption cross section (MAC) values of black carbon (BC) particles at the study site using the linear regression between aethalometer-based absorption coefficient and filter-based EC concentration. BC particles observed at 880 nm is mainly emitted from combustion of fossil fuels, and their concentration is typically reported as equivalent BC concentration (eBC). eBC concentration calculated using MAC value of $7.77m^2/g$ at wavelength of 880 nm, which was proposed by a manufacturer, ranged from 0.3 to $7.4{\mu}g/m^3$ with an average value of $1.9{\pm}1.2{\mu}g/m^3$, accounting for 7.3% (1.5~20.9%) of $PM_{2.5}$. The relationship between aerosol absorption coefficients at 880 nm and EC concentrations provided BC MAC value of $15.2m^2/g$, ranging from 11.4 to $16.2m^2/g$. The eBC concentrations calculated using the estimated MAC of $15.2m^2/g$ were significantly lower than those reported originally from aethalometer, and ranged from 0.2 to $3.8{\mu}g/m^3$, with an average of $1.0{\pm}0.6{\mu}g/m^3$, accounting for 3.7% of $PM_{2.5}$ (0.8~10.7%). Result from this study suggests that if the MAC value recommended by the manufacturer is applied to calculate the equivalent BC concentration and radiative forcing due to BC absorption, they would result in significant errors, implying investigation of an unique MAC value of BC particles at a study site.