• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.63-70
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• 2005

Optical Line Patternator(OLP) has been applied to get a distribution of the spray at high ambient pressure. OLP is a combined technique of extinction measurement and image processing. The attenuated intensity of laser beam after traversing spray region was measured by using a photo-detector, and the line image of Mie-scattering was captured simultaneously in the path of each laser beam by using a CCD camera. The distribution of extinction coefficient in the spray is obtained by processing these data with the algebraic reconstruction technique. From the distribution of extinction coefficient, the surface distribution of spray can be reconstructed. OLP does not use laser sheet but use laser beam so that the noise effect of multiple scattering, caused by increasing number density of droplet in high pressure environment, is reduced drastically. OLP is expected as a suitable method which can investigate the characteristics of relatively large spray under the high pressure environment such as liquid rocket engine.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.725-732
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• 2000

Laser induced incandescence (LII) method is frequently used to measure soot volume fraction in flames. In this study, experiments were performed to measure soot volume fraction in coaxial diffusion flame using LII method and calibrated with laser scattering/extinction method. The effects of laser intensity (>$1{\times}10^8W/cm^2$), laser wavelength (532nm, 1064nm) and detection wavelength (400nm, 600nm) on the LII signal were investigated. On the range of $4{\times}10^8{\sim}8{\times}10^8W/cm^2$ there were no effects of laser intensity on LII signal. Except these ranges, LII signal was increased with laser intensity. For the long gate width, the LII signals of the higher laser intensity (>${\vartheta}(GW/cm^2)$) cases had better correlation with soot volume fraction which were measured by laser extinction method compared with lower laser intensity cases. The errors of 2-dimensional cases at the calibration height were approximately 50% regardless of laser wavelength.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.3
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• pp.378-386
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• 2009

The effect of fuel mixing on soot structure with methane, ethane, and propane to ethylene-base counterflow diffusion flames has been investigated by measuring the volume fraction, number density, and particle size of soot by adopting the light extinction/scattering techniques. The experimental result showed that the mixing of ethane and propane in ethylene diffusion flame increased soot volume fraction while the mixing of methane decreased. As compare to the ethylene-base flame, the diameters of soot particles for mixture flames are slightly smaller. While the soot number densities for the mixture flames are much higher. Thus, the increase in the soot volume fraction can be attributed to the appreciably increased soot number density by the fuel mixing.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.3-13
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• 2005

The optical patterantor provides the high resolution and quantitative information of the spray. Fuel distribution and Sauter Mean Diameter (SMD) can be measured from fluorescence and Mie-scat-tering images. To correct the attenuation of the laser beam and signal in dense spray region, the method to find the geometric mean of the signal intensities obtained from two cameras was evaluated and verified in a solid-cone spray. In high pressure environment, the increased number density of the droplets cause multiple scattering. The optical patternation technique using a laser beam instead of a laser sheet was applied to minimize the multiple scattering problem. The pattern of a coaxial spray was changed from hollow-cone to solid-cone shape, and the spray angle was reduced as the ambient pressure increased from 0.1 to 4.0 MPa.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.75-82
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• 1996

Laser induced incandescence, LII, recently developed technique for measuring soot concentration in flames, can overcome most of limitations of conventional laser extinction measurement. In this study, experiments were performed to investigate the effect of laser intensity, detection wavelength, and also laser beam quality on both LII signal at a particular position and peak-to-centerline LII signal ratio. The results of LII signal with increasing laser intensity shows its near-independence of laser intensity once threshold level of laser intensity has been reached. However, this near-independence depends on laser beam quality and the incident optical setup. The peak-to-centerline LII signal ratio slowly but continuously increases with laser power. This fact is due to the dependence of LII signal on particle mean diameter. LII signal is attenuated during it passes through the flame containing soot particles. The attenuation rate is inversely proportional to detection wavelength. In this study, LII signal at 680 nm band is 10% greater than the signal at 400 nm band.

• Korean Journal of Optics and Photonics
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• v.33 no.1
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• pp.1-10
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• 2022

In this study we introduce a new method for high-spatial-resolution continuous wave (CW) aerosol lidar that has a high spatial resolution in the near field and a low spatial resolution at long distances. A normal lidar system uses a nanosecond-pulse laser and measures the round-trip TOF between the aerosol and laser to obtain range resolution. In this study, however, we propose a new type of spatially resolving aerosol lidar that uses laser-scattering images. Using a laser-light-scattering image, we have calculated the distance of each scattering aerosol image for a given pixel, and recovered the short-range aerosol extinction. For this purpose, we have calculated the distance image and the contribution range of the aerosol to the given one-pixel image, and finally we have calculated the extinction coefficients of the aerosol with range-resolved information. In the case of traditional aerosol lidar, we can only obtain the aerosol extinction coefficients above 400 m. Using our suggested method, it was possible to extend the range of the extinction coefficient lower then several tens of meters. Finally, we can remove the unknown short-range region of pulsed aerosol lidar using our method.

• Korean Journal of Optics and Photonics
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• v.32 no.3
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• pp.120-125
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• 2021

We have developed a linearly polarized high-power Yb-doped fiber laser in the master oscillator power amplifier (MOPA) scheme for efficient spectral beam combining. We modulated the phase of the seed laser by pseudo-random binary sequence (PRBS), with the bit length optimized to suppress stimulated Brillouin scattering (SBS), and subsequently amplified seed power in a 3-stage amplifier system. We have constructed by coiling the polarization-maintaining (PM) Yb-doped fiber, with core and cladding diameters of 20 ㎛ and 400 ㎛ respectively, to a diameter of 9-12 cm for suppression of the mode instability (MI). Finally, we obtained an output power of 1.004 kW with a slope efficiency of 83.7% in the main amplification stage. The beam quality factor M² and the polarization extinction ratio (PER) were measured to be 1.12 and 21.5 dB respectively. Furthermore, the peak-intensity difference between the Rayleigh signal and SBS signal was observed to be 2.36 dB in the backward spectra, indicating that SBS is successfully suppressed. In addition, it can be expected that the MI does not occur because not only there is no decrease in slope efficiency, but also the beam quality for each amplified output is maintained.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.390-401
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• 2005

In this study, extinction limit extension of unsteady $(CH_{4}+N_{2})$/air diffusion flames was investigated experimentally. A spatially locked flame in an opposing jet burner was perturbed by linear velocity variation, and time-dependent flame luminosity, transient maximum flame temperature and OH radical were measured over time with the high speed camera, Rayleigh scattering method and OH laser-induced fluorescence, respectively. Unsteady flames survive at strain rates that are much higher than the extinction limit of steady flames, and unsteady extinction limits extend as the slope of the strain rate increases or the initial strain rate decreases. We verified the validity of the equivalent strain rate concept by comparing the course of unsteady extinction process and steady extinction process, and it was found that the equivalent strain rate concept represents well the unsteady effect of a convective-diffusive zone. To investigate the reason of the unsteady extinction limit extension, we subtracted the time lag of the convective-diffusive zone by using the equivalent strain concept. Then the modified unsteady extinction limits become smaller than the original unsteady extinction limits, however, the modified unsteady extinction limits are still larger than the steady extinction limits. These results suggest that there exist the unsteady behavior of a diffusive-reactive zone near the extinction limit due to the chemical non-equilibrium states associated with unsteady flames.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.3
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• pp.301-306
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• 2010

DME(Di-Methyl Ehter, $CH_3OCH$) is currently attracting worldwide attention due to its environmentally friendly characteristics. Until now it was researched as a major alternative fuel of diesel automobile because it is a clean fuel producing low soot. Therefore, in this study, in order to investigate the effect of DME mixing on number density and size of soot particle, DME has been mixed in opposed-flow ethylene diffusion flame with the mixture ratios 5%, 14% and 30%. A laser extinction/scattering technique has been adopted to measure the volume fraction, number density, and size of soot particles. The experimental results showed that the soot concentration of mixture flames with the mixture ratios 5% and 14% produces soot more, even though that of 30% was decreased. This means that even though DME has been known to be a clean fuel for soot formation, the mixing of DME in diffusion flame of ethylene, where acetylene maintains high concentration in soot formation regions, could produce enhanced production of soot.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.725-730
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• 2014

The effect the diameter of silver nanorod arrays whose distance between the nanorods was uniform at 65 nm have on Surface-enhanced Raman Scattering (SERS) has been studied by varying the diameter from 28 to 51 nm. Nanorod length was fixed at approximately 62 nm, which is the optimum length for SERS by excitation with a 632.8 nm laser line. The transverse and longitudinal modes of the surface plasmon of these silver nanorods were near 400 and 630 nm, respectively. The extinction of the longitudinal mode increased with increasing nanorod diameter, while the transverse mode did not change significantly. High-quality SERS spectra of p-aminothiophenol and benzenethiol adsorbed on the tips of the silver nanorods were observed by excitation with a 632.8 nm laser line. The SERS enhancement increased with increasing nanorod diameter. We concluded that the SERS enhancement increases when the diameter of silver nanorods is increased mainly by increasing the excitation efficiency of the longitudinal mode. The enhancement factor for the silver nanorods with a 51 nm diameter was approximately $2{\times}10^7$.