• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.49-54
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• 1989

Thin solid film systems polarizing beam splitter and disk amplifier used in the high power laser system ({{{{ lambda }}0=1060nm) are designed by computer aided optimization technique. Extinction ratio of designed polarizing beam splitter for incidence angle 30$^{\circ}$, 45$^{\circ}$, 55.60$^{\circ}$ are 1:93, 1:895, 1:1991. respectively. Maximum reflectance of designed thin film system of disk amplifier is less than 3% for pumping band (500-900nm) and 0.15% for laser beam. Further, SiO film chosen as one of the suitable thin films in the high power laser system is prepared by the sol=-gel process which gives high damage threshold. When the withdrawal speed is 6.15cm/min -16.62 cm/min and the mixing ratio is in the range of 1 mol (ethylsilicate): 4-8mol(ethylalcohol) : 2mol(water), the thickness of deposited film is in the range of 500{{{{ ANGSTROM }}-1500{{{{ ANGSTROM }}.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1348-1354
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• 2002

We investigate the flame behavior and spatial distribution of OH, PAHs and soot in a confined buoyant diffusion flame with decrease of the coflowing air flow rate. Direct photographs and Schlieren images represent that flame is Ally occupied by blue flame and becomes unstable, which is partially detached to the fuel nozzle tip in a near extinction flame under extremely reduced oxidizer condition. Laser induced fluorescence profiles clearly shows that OH is still generated in near-extinction flame, although intensity becomes weak with decreasing air flow rate. But soot scattering image cannot be seen any more in an oxidizer deficient ambience and simultaneously the PAHs are widely distributed downstream. These results are due to that a decrease of oxygen concentration in the combustion chamber leads to a temperature drop of flame, as a consequence, to a delay in soot growth and to a expanding of the PAHs, as soot precursors.

• 한국화재소방학회논문지
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• 제30권1호
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• pp.37-42
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• 2016

바이오디젤(Soy Methyl Ester, B100)과 디젤(Ultra Low Sulfur Diesel, ULSD)의 연소과정에서 발생되는 연기입자의 무차원 광소멸계수를 측정하였다. 무차원 광소멸계수는 633 nm의 He-Ne 레이저를 이용하여 광학적 방법으로 측정된 연기입자의 체적분율과 중력식 필터법에 의해 채집된 연기입자의 체적분율을 비교하여 결정하였다. 633 nm 대역에서 측정된 평균 무차원 광소멸계수는 각각 바이오디젤의 연기입자가 11.8, 디젤 연기입자가 11.1으로 측정 불확도 범위(${\pm}10.1%$) 내에서 거의 유사하였다. 다만, 라만 spectrum 분석결과를 통해 각 연료에서 발생된 연기입자 간의 광소멸(광흡수/광산란) 특성은 서로 상이할 수 있음을 확인할 수 있었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1997년도 제15회 KOSCO SYMPOSIUM 논문집
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• pp.1-11
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• 1997

The soot and OH radical distributions have been experimentally studied in ethylene and propane laminar diffusion flames. The integrated soot volume fraction was measured along the centerline of a flame using a laser light extinction method. Planar laser light scattering and PLIF techniques are employed for the soot and OH radical distribution measurements utilizing Nd:YAG laser and OPO, FDO system. The concentration of OH radical is rapidly decreased at the edge of sooting region, which implies the importance of OH radical species on the soot oxidation process. For ethylene flames, the addition of air in fuel moves the OH radical distribution towards the center line of a flame at the soot oxidation region, while the concentration of OH radical remains relatively high at the soot formation region. The interaction between soot particles and OH radicals becomes more active with fuel-air at the soot oxidation region. For propane flames, however, any indication of the increased interaction between soot particles and OH radicals with fuel-air was not noticed.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2093-2096
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• 2014

2H-azirine, a less known acetonitrile isomer, is observed in matrix IR spectra from the precursor exposed to radiation from laser ablation of transition-metals. Its vibrational characteristics confirm the previous results, and those for the deuterated and $^{13}C$ substituted isotopomers are also newly reported. The weak absorptions are traced to the low production yield due to its high energy and low extinction constants. IRC computations reveal smooth inter-conversion between 2H-azirine and $CH_2NCH$, providing a rationale for the observed variation of their relative contents during photolysis.

• E2M - 전기 전자와 첨단 소재
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• 제11권11호
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• pp.28-36
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• 1998

Widely tunable diodes integrated with periodically sampled and chirped DBR(distributed Bragg reflector) and an EA(electroabsorption) modulator are analyzed dynamically using the improved largesinal time-domain model. The tuning characteristics of sampled- and chirped-grating DBR laser diodes are demonstrated theoretically. The results of the simulation agree well with those of the experiment. And the intensity-modulation properties of the laser diodes integrated with an EA modulator are calculated. It is shown that the external modulation has the lower frequency chirp by 1/20 for the same extinction ratio than the direct modulation, and also the short pulse train can be generated using the optical gating of an EA modulator.

• 한국대기환경학회지
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• 제25권5호
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• pp.450-458
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• 2009

The range-dependent overlap factor of a lidar system can be determined experimentally if a Raman backscatter signal by molecule is measured in addition to the usually observed elastic backscatter signal, which consists of a molecular component and a particle component. The direct determination of the overlap profile is presented and applied to a lidar measurement according to variation of telescope field-of-view and distance between telescope and transmitting laser. The retrieval of extinction coefficient by Raman method can generate high errors for heights below planetary boundary layer if the overlap effect is ignored. The overlap correction method presented here has been successfully applied to experimental data obtained in Gwangju, Korea.

• 한국인쇄학회지
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• 제29권3호
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• pp.17-30
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• 2011

The polarizer is an important optical element used in a variety of applications. Nano-wire grid polarizers in the form of sub-wavelength metallic gratings are an attractive alternative to conventional polarizers, because they provide high extinction ratio. This study has been carried out to fabrication of the 17inch area size nano-wire grid polarizer(NWGP) The master for NWGPs with a pitch of 200nm and the area size $730mm{\times}450mm$ were fabricated using laser interference lithography and aluminum sputtering and wet etching. And The NWGP fabrication process was using by the Roll to-Roll UV imprinting and was applied to flexible PET film. The results were a transmission of light (Tp) 46.7%, reflectance (Rs) 40.1% and Extinction ratio of above 16 for the visible light range.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.391-397
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• 2006

The soot yield has been studied by a premixed propane-oxygen-inert gas combustion in a specially designed disk-type constant-volume combustion chamber to investigate the effect of pressure, temperature and turbulence on soot formation. Premixtures are simultaneously ignited by eight spark plugs located on the circumference of chamber at 45 degrees intervals in order to observe the soot formation under high temperature and high pressure. The eight converged flames compress the end gases to a high pressure. The laser schlieren and direct flame photographs with observation area of 10 mm in diameter are taken to examine the behaviors of flame front and gas flow in laminar and turbulent combustion. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in-situ laser extinction technique and simultaneously the corresponding burnt gas temperature by the two-color pyrometry method. The changes of pressure and temperature during soot formation are controlled by varying the initial charging pressure and the volume fraction of inert gas compositions, respectively. It is found that the soot yield increases with dropping the temperature and raising the pressure at a constant equivalence ratio, and the soot yield in turbulent combustion decreases as compared with that in laminar combustion because the burnt gas temperature increases with the drop of heat loss for laminar combustion.

• 해양환경안전학회지
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• 제16권3호
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• pp.301-306
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• 2010

DME는 환경 친화적인 특성으로 인해 현재 전 세계적으로 주목을 받고 있다. 지금까지 DME는 매연을 적게 생산하는 청정 에너지라는 특성으로 인해 디젤 자동차의 주요 대체 에너지로서 연구되어 왔다. 이에 본 연구에서는 에틸렌 대향류 확산화염에 DME를 5%, 14% 및 30% 혼합했을 때, DME의 혼합 비율에 따른 매연의 수밀도 및 크기에 대한 영향을 조사하였다. 레이저 투과법 및 산란법을 이용해 수밀도 및 크기를 측정하였다. 그 결과 DME를 30% 혼합한 경우에는 매연이 감소한 반면, 5%와 14%의 혼합 비율에서는 매연이 증가하는 경향을 나타내었다. 이 결과는 DME가 매연 생성이 적은 청정 연료로 알려진 것과는 달리 에틸렌 확산화염 내에서는 DME의 혼합에 따라 매연 생성이 증가될 수 있다는 것을 의미한다.