• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2256-2258
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• 1999

This paper describes preliminary discussions on spatial distribution of NO density, which is mostly contained in simulated NOx exhaust, between a wire-cylinder geometry discharge gaps by using Laser Induced Fluorescence(LIF) Spectroscopy, Spatial distribution of NO density will be measured with varying NO concentrations from 166 to 644 [ppm] and diameters of central electrode from 6 to 10mm. Pulsed Nd:YAG laser. Optical Parametric Oscillator(OPO), and Frequency Doubler are used to excite NO molecules to their excited state.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1807-1809
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• 1997

The salt contamination on the surface of the porcelain insulators used electric power systems causes flash-over accidents. Therefore the quantity of salt contamination should be monitored not to exceed a limit. In this study, we tried laser aided measurement of salt contamination. The Nd:YAG laser beam was focused on the surface of the porcelain insulators which were artificially contaminated, and we detected the D-Line (${\cong}589nm$) of spontaneous emission from the excited sodium atoms with a PMT and an oscilloscope. And we deduced the relation between the detected signals and degree of salt contamination.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1905-1907
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• 1997

The experiments of laser-guided de discharge were carried out by using pulsed Nd:YAG laser radiation at low air pressure ranging from 0.3 to 20 torr. The minimum laser-guided de discharge voltages($V_{MD}$) at given pressure and distances between anode and cathode electrode were obtained. In order to generate TEM(transverse electromagnetic waves) modes, a pinhole was installed between a rod and a half mirror, and its diameter was adjusted from 6mm to 1.7mm. And then, we investigated the characteristics of laser-guided de discharge corresponding to different TEM modes. As a result, it was found that $V_{MD}$ at $TEM_{00}$ mode was lower than $V_{MD}$ at multimodes.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.169-176
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• 1996

The specimens which were prepared from $\alpha$-Si3N4 with additions of YAG(3Y2O3.5Al2O3)-10 wt% and various AlN contents were sintered in N2 atmosphere at 1$700^{\circ}C$ The effect of $\alpha$,$\beta$-solid solution contents and sintering time on mechanical properties were investigated. As the content of $\beta$-solid solution and sintering time increased the hardness is reduced but the hardness of specimen sintered over 10 hours is constant irrespective of sintering time. While the fracture toughness increased with increasing of $\beta$-solid solution and sintering time. The fracture toughness of specimen with 80% $\beta$-solid solution content increased from 3.89 to 6.66 MPam1/2 with sintering sintering up to 20 hours/ But the amount of increased fracture toughness of specimen with below 20% $\beta$-solid solution content is not significant.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1308-1314
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• 1995

Changes in phase and microstructure were investigated in the SiC-AlN ceramics prepared by pressureless sintering using yttrium aluminum garnet (YAG) as a sintering aid at 200$0^{\circ}C$ and 210$0^{\circ}C$. The SiC/AlN ratio made a remarkable difference in densification, phase relations and the morphology of grains. In the AlN-rich composition, major phase was 2H and microstructure was composed of the densified equiaxed grains irrespective of the sintering temperatures. While those sintered at 200$0^{\circ}C$ were porous with major phase being 3C, the rod-like and the equiaxed grains were coexisted when sintered at 210$0^{\circ}C$ in the SiC-rich composition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.50-53
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• 2001

Flame propagation during the initial stages of ignition in a non-premixed swirl, having some of characteristics of the primary zone of an aero gas turbine combustor, has been investigated. Nd:YAG laser was adopted as the principal ignition source to allow arbitrary placing of the ignition site i subsequent flame development was monitored using a natural light high speed filming technique for many ignition site at two different swirl ratios and an overall equivalence ratio of 0.9. For ignition offset from the burner centreline, buoyancy force associated with radial pressure gradient produced a strong inward movement of the flame kernel. At the burner exit. flame kernels invariably developed into cylindrical form and a 'radial confinement /axia expansion' (RCAE) process was observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.53-57
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• 2007

고속회전의 원심력으로 연료를 공급하고 액체연료의 미립화를 초래하는 회전연료분무장치에 대한 분무특성 시험연구를 수행하였다. 특정한 공간상에 존재하는 액적의 특성을 이해하고자 고속회전 연료분사시스템을 설계 제작하였다. 시험장치는 고속으로 회전하는 Spindle, 회전연료노즐, 가압식 물탱크, 아크릴 케이스로 구성하였다. 액적의 크기와 속도를 측정하기 위해 PDPA(Phase Doppler Particle Analyzer)시스템을 사용하였고, ND-Yag Laser를 사용하여 분무를 가시화 하였다. 시험결과 고속회전 연료분사시스템의 분무특성을 확인할 수 있었고, 회전속도는 액적 크기, 속도, 분무각 및 분무패턴 등의 분무특성에 주요한 영향을 미치는 것으로 확인되었다.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.239-243
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• 1992

We have investigeted the interference phenomena of the second harmonic waves of Nd:YAG laser generated at KDP single crystals and the nitrogen CARS signals. To get the phase difference between the successively generated nonlinear optical signals, a phase shifting unit made of BK-7 glass and a high pressure gas cell are used. Coherence lengths of several samples for the nonlinear signals are measured. Adjusting the thickness of the phase shifting unit where the CARS signals make destructive interference completely, the CARS spectrum of nitrogen suppressed over wide wavelength range is obtained. Also, we have observed the change in degree of suppression of the spectrum for the variation of the thickeness of the phase shifting unit.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.26-30
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• 1997

A wide dynamic range heterodyne interferometer scheme using intermode beat between a stabilized, dual frequency He-Ne laser beam has been applied for a measurement of optical thickness of an optical medium. Resolution of the optical thickness measurement is about $\pm$ 1.74 ${\mu}{\textrm}{m}$. Using this technique, we are able to determine the optical thickness of an organic dye film. We also obtain a map of the optical thickness variations over a surface of the film

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.220-221
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• 2003

Intracavity second harmonic generation of diode pumped solid state lasers in the visible and ultraviolet regions provide efficient, compact and robust light sources for various applications, such as optical data storage, material processing, spectroscopy and bioanalysis. Advantages of neodymium vanadate (Nd：$YVO_4$) as a gain medium for intracavity-doubled lasers over Nd：YAG lie in the facts that the gain spectrum consists of a single line with short absorption depth, and that the stimulated emission cross sections are larger. (omitted)