• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.499-505
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• 1997

A non-invasive technique to measure absorption and scattering coefficients was investigated The reflected backscattered light from the surface of phantom and biological tissue was obtained by using a time-correlated single photon counting system in pico-second time domain. The absorption and scattering coefficients were acquired by the time of peak and asymptotic behavior of the time-resolved reflectance curve and agreed well the ones that is obtained with deconvolution method It was found that the approximation method was good for biological medium to calculate optical properties due to its convenience and accuracy.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.434-440
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• 2000

We fabricated a high power Nd:YAG laser pumped by a 1 kW diode laser with a Lambertian-type diffusive reflector. Maximum cw power of 500 W with a slope efficiency of 49%, which corresponds to an optical efficiency of 46.7%, was obtained from a short linear resonator when a 5 mm rod was used. The efficiencies decreased when a 6 mm rod was used, due to the poor quality of the absorption distribution in the rod. The measured beam quality factor of 70, which is slightly smaller than the value calculated from the measured thermal focal lengths, shows that the absorption distribution in the rod is fairly uniform. iform.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.429-434
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• 2012

Ignition delay of micro/nano aluminum particles is caused by aluminum oxide shell. The method of minimizing this ignition delay is proposed in the study. Generating and heating of particles are processed at the same time. As soon as heated particles are produced, they immediately contact with oxygen. Chemical reaction is induced on the contact surface instead of crystallization of oxide shell. Finally particles are ignited. Aluminum particles are generated by laser ablation on an aluminum plate using Nd:YAG pulse laser. Injected particles are confirmed through visualization of particles using scattering method. $CO_2$ continuous laser supplies heat to aluminum plate and generated particles. Trace of burning particles is observed in the experiment.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.1-1
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• 2002

PLLIF(Planar Laser Liquid Induced Fluorescence) 기법은 분무장을 교란시키지 않고 고해상도의 2차원 질량분포를 빠르게 측정할 수 있기 때문에 기존의 기계적인 분무 분포 측정방법의 한계를 극복하였을 뿐만 아니라 접근이 불가능하였던 인젝터 근방의 분무에 대한 중요한 정보를 제공하고 있다. 그러나 레이저 광을 받은 액적에 의한 산란광의 강도가 클 경우에는 인접한 액적들을 형광시킬 수 있고 액적의 형광신호가 액적들을 통과하면서 감쇠되는 이차산란에 의한 오차는 PLLIF 기법의 정량화에 가장 큰 난점으로 인식되고 있다. 특히 이러한 현상은 분무 분포의 밀도가 높고 액적의 크기가 클수록 강하게 나타나는데, 액체로켓에서 일반적으로 사용되고 있는 like-doublet 인젝터는 이러한 분무 특성을 갖는다. 따라서 Mechanical Patternator 및 PDPA(Phase Doppler Particle Analyzer)로부터 측정한 like-doublet 인젝터의 분무 질량 분포 결과와 비교하여 이차산란에 의한 오차를 파악하여 PLLIF 기법의 적용 가능성을 진단하였다.

• Journal of the KSME
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• v.33 no.12
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• pp.1063-1068
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• 1993

왕복식엔진에서 연소과정은 실린더내 유체유동에 지배되므로 최적조건의 엔진설계를 위해서는 실린더내 유체유동을 효과적으로 이용하는 것이 필요하다. 연소과정에 중요한 영향을 미치는 압축말기 연소실내 난류강도는 흡입과정시 생성된 유동의 에너지가 압축과정을 거치면서 작은 스케일의 에디(eddy)로 깨지면서 발생된다. 연소과정시 이러한 에디들은 초기화염생성을 촉진 시키고 화염전파속도를 증진시키는 역할을 함으로써 실린더내 유체유동에 대한 이해증진을위해 실린더내 평균속도 및 난류유동을 측정하는 연구들이 많이 진행되고 있다. 엔진유동은 매사이 클의 유동이 엄밀히 주기적인 운동을 하지 않고, 각 사이클의 유동이 비정상유동을 하며, 유동의 생성 및 소멸이 매우 짧은 특성을 가진다. 따라서 산란입자가 측정체적을 통과할 때 속도데이 터가 발생하는 LDV(laser Doppler velocimetry) 측정에 있어서 레이저빔의 산란광노이즈 감소와 산란입자의 효율적인 공급으로 데이터 발생률을 높이는 것이 어려운 점이다. 이 글에서는 엔진 유동의 LDV측정시 고려해야 할 문제점들, 실험장치구성, 그리고 데이터처리 방법과 주요측정 결과에 대해 본 연구팀에서 지금까지 수행한 연구결과를 토대로 하여 기술하고자 한다.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.337-344
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• 1995

We have detected the resonant stimulated Raman scattering signal when the Q-switched Nd:YAG laser beam are incident on the $35~62{\mu}m$ sized water droplet as pump beam. The signals appeared as uniformly spaced peaks and the intervals between peaks become narrow as the droplet size increases. Also we have confirmed the morphology dependent resonances (MDR's) characteristic of the stimulated Raman scattering signal when the water droplet becomes nearly spherical shape after two water droplets are coupled to a droplet. The error in the measured intervals between MDR's of same mode order is about 5%.out 5%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.502-510
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• 2009

Laser Inertial Navigation System(LINS) consists of Ring Laser Gyroscopes(RLG) and accelerometers. RLG has a lock-in region in which there is zero output for input angular rates less than 0.1deg/sec. The lock-in region is generated by the imperfect mirrors in RLG. To avoid the lock-in region, sinusoidal motion which is called dither motion is applied on RLG. Therefore without the fault in LINS, the dither motion must be measured by RLG/accelerometer. In this paper, we propose the method to detect the fault of LINS through checking out whether or not the dither motion is always measured by RLG/accelerometer using the Fast Fourier Transformation(FFT) on the real time. The feasibility of the fault detection method proposed in this paper is verified through the stationary and van test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.241-242
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.373-374
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• 2007

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.87-88
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• 2008