• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.53-59
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• 2019

LIBS plug, a simplified laser-induced breakdown spectroscopy(LIBS) device with the purpose of measuring the fuel distribution inside the combustion chamber, was developed and manufactured. The LIBS plug receives only two wavelengths (H:656.3 nm, O: 777 nm) that are closely related to the equivalence ratio in the overall spectrum. The calibration curve between the signal of the LIBS plug and the equivalence ratio was constructed, and the fuel distribution of gasoline-air and LPG-air mixtures was measured using the LIBS plug.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.370-376
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• 2016

Corrosion on the surface of a structure can generate cracks or cause walls to thin. This can lead to fracturing, which can eventually lead to fatalities and property loss. In an effort to prevent this, laser imaging technology has been used over the last ten years to detect thin-plate structure, or relatively thin piping. The most common laser imaging was used to develop a new technology for inspecting and imaging a desired area in order to scan various structures for thin-plate structure and thin piping. However, this method builds images by measuring waves reflected from defects, and subsequently has a considerable time delay of a few milliseconds at each scanning point. In addition, the complexity of the system is high, due to additional required components, such as laser-focusing parts. This paper proposes a laser imaging method with an increased scanning speed, based on excitation and the measurement of standing waves in structures. The wavenumber of standing waves changes at sections with a geometrical discontinuity, such as thickness. Therefore, it is possible to detect defects in a structure by generating standing waves with a single frequency and scanning the waves at each point by with the laser scanning system. The proposed technique is demonstrated on a wall-thinned plate with a linear thickness variation.

• Korean Journal of Optics and Photonics
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• v.9 no.6
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• pp.380-384
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• 1998

As the development of ultrahigh power laser system, the laser mirrors must require high-resistant and effectively cooled. So, the study for the optical multilayer systems having large thermal diffusivity become important. In this study, we designed and fabricated two-layer anti-reflection (AR) optical coating samples, in different evaporation conditions of coating speeds (10, 20 $\AA$/s) and substrate temperatures (50, 100, 150, 20$0^{\circ}C$), using two dielectric materials $MgF_2$ and ZnS which have different refractive indices and measured the through-plane thermal diffusivity by using photoacoustic effect. The optical thicknesses of $MgF_2$ and ZnS layer were fixed as 5/4λ (λ=514.5nm) and λ, respectively, and the thermal diffusivity of the samples fabricated in the different conditions was obtained from the measured amplitude of photoacoustic signals by changing chopping frequency of $Ar^+$ layer beam. The results told us that the thermal diffusivity of the sample fabricated in the condition of 10 $\AA$/s and 15$0^{\circ}C$ showed the largest value.

• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.217-222
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• 2009

In this paper, a low-cost hybrid-integrated tunable laser is realized using a polymer-ring resonator-based add/drop filter reflector and a reflective semiconductor optical amplifier. The add/drop filter reflector, composed of a double-ring resonator with different radii, can have characteristics of selective wavelength reflection and wide wavelength tuning with an aid of vernier effect derived from the radii difference. By hybrid-integrating the reflective semiconductor optical amplifier with the add/drop filter reflector, a tunable laser can be realized through an active alignment method. The hybrid laser exhibited a single mode lasing with side mode suppression ratio of 26 dB and full width half maximum of 0.03 nm. In addition, applying a low current as small as 25 mA onto electrodes over add/drop filter reflector, a wavelength tuning range of 17 nm could be obtained.

• Korean Journal of Optics and Photonics
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• v.28 no.4
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• pp.135-140
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• 2017

In this paper, we report measured results for an all-fiber $7{\times}1$ pump combiner based on an optical fiber chip for high-power fiber lasers. An optical-fiber chip was fabricated by etching a fiber, having core and cladding diameters of 20 and $400{\mu}m$, in the longitudinal direction. To both ends of the etched chip, we spliced input and output fibers. First, we tied together seven optical fibers, having core and cladding diameters of 105 and $125{\mu}m$ respectively, in a cylindrical bundle and spliced them to the $375-{\mu}m$ end of the optical-fiber chip. Then, we attached an output DCF with core and cladding diameters of 25 and $250{\mu}m$ to the $250-{\mu}m$ end of the optical-fiber chip. Finally, the fabricated $7{\times}1$ pump combiner showed an average optical coupling efficiency of about 90.2% per port. This chip-based pump combiner may replace conventional pump combiners by massive production of fiber chips.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.5
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• pp.555-563
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• 2011

The goal of image calibration is to find a relation between image and world coordinates. Conventional image calibration uses physical camera model that is able to reflect camera's optical properties between image and world coordinates. In this paper, we try to calibrate images distortion using performance criterion-based polynomial model which assumes that the relation between image and world coordinates can be identified by polynomial equation and its order and parameters are able to be estimated with image and object coordinate values and performance criterion. In order to overcome existing limitations of the conventional image calibration model, namely, over-fitting feature, the performance criterion-based polynomial model is proposed. The efficiency of proposed method can be verified with 2D images that were taken by laser scan camera.

• Journal of Oral Medicine and Pain
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• v.30 no.2
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• pp.277-285
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• 2005

The purpose of this study was to evaluate photothermal effect of laser, which eliminates and reduces bacteria causing periodontal disease, on treatment of periodontal disease. This study included subjects with moderate periodontitis who visited the Department of Oral Medicine, College of dentistry, Yonsei University. The subjects were divided into experimental group, where Argon laser treatment was used, and control group, where conventional subgingival curettage was used. Gingival fluids from each subject were collected prior and after 1 week of the treatment, and changes in number of bacterial colonies cultured from aerobic as well as anaerobic bacteria responsible for the periodontal disease, and changes in clinical indices related to the periodontal disease, such as plaque index, gingival index, sulcus bleeding index, were analysed. As a result, the number of bacterial colonies of aerobic and anaerobic bacteria reduced after 1 week of the treatment in both groups, especially the bacterial colonies of anaerobic bacteria which showed statistically significant reduction(p<0.1). However, there was no significant difference between the experimental group and the control group. Clinical indices including plaque index, gingival index, sulcus bleeding index were reduced after 1 week of the treatment in both groups. In the experimental group, gingival index(p<0.1) and sulcus bleeding index(p<0.01) showed significant reduction, and, in the control group, sulcus bleeding index(p<0.01) showed significant reduction. However, there were no significant differences in each indices between the two groups. The above results suggest that Argon laser could be used as a substitute of conventional subgingival curettage, or in combination with subgingival curettage which would increase the effect of the treatment. Although the possibility of clinical application of Argon laser was observed in this study, more randomized-controlled research, including acquirement of sufficient samples as well as long-termed follow up, would be necessary before clinically effective application of Argon laser.

• Journal of the Korean Electrochemical Society
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• v.3 no.1
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• pp.19-24
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• 2000

It is increasingly necessary to use poly-Si n's as high resolution and integration of Tn for LCD. Excimer Laser Crystallization (ELC) of a-Si is mainly used as a low temperature process. But the ELC method for the fabrication of poly-Si has the eruption problems associated with hydrogen in the a-Si film. So we need a dehydro-genation process additionally. Hydrogen in a-Si film can degrade the quality of poly-Si film and electrical properties of device due to the hydrogen eruption and voids which occur during the excimer laser annealing. In this study, we propose mesh-type PECVD as the a-Si film deposition method for achieving the low concentration hydrogen. Mesh-type PECVD was found to reduce the hydrogen content substantially. We could obtain a as-deposited a-Si film with hydrogen contents less than $1\%$ at $300^{\circ}C$. We also investigated the behavior by XeCl excimer laser annealing of a-Si fabricated by mesh-type PECVB. As a result, we were able to confirm the broad process window in contrast to the narrow process range typically obtained in ELC. Hydrogen eruption was not observed in poly-Si films after ELC These results suggests that mesh-type PECVD is a viable method to achieve the low hydrogen content a-Si and improve the process windows for ELC.

• Economic and Environmental Geology
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• v.40 no.5
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• pp.563-574
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• 2007

Laser induced breakdown spectroscopy (LIBS) is a recently developed analytical technique that is based upon the measurement of emission lines generated by atomic species close to the surface of the sample, thus allowing their chemical detection, identification and quantification. With powerful advantages of LIBS compared to the conventional analytical methodology, this technique can be applied in the detection of heavy metals in the field. LIBS allows the rapid analysis by avoiding laborious chemical steps. LES have already been applied for the determination of element concentration in a wide range of materials in the solid, liquid and gaseous phase with simplicity of the instrument and diversity of the analytical application. These feasibility of rapid multi elemental analysis are appealing proprieties for the in-situ analytical technique in geochemical investigation, exploration and environmental analysis. There remain still some limitations to be solved for LIBS to be applied in soil environment as an in-situ analytical technology. We would like to provide the basic principle related to the plasma formation and laser-induced breakdown of sample materials. In addition, the matrix effect, laser properties and the various factors affecting on the analytical signal of LIBS was dealt with to enhance understanding of LIBS through literature review. Ultimately, it was investigated the feasibility of LIBS application in soil environment monitoring by considering the basic idea to enhance the data quality of LIBS including the calibration method for the various effects on the analytical signal of LIBS.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.307-312
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• 2017

Laser cladding has some advantages compared to conventional cladding technologies such as arc welding and thermal spraying. Laser cladding produces a metallurgically well-bonded clad layer with a lower dilution ratio and few defects. Based on the characteristics of a 1-pass clad layer with many parameters, which were investigated in a previous report, it was found that it was essential to overlap a 1-pass clad layer when cladding a large area. In this study, the shape differences of multi-pass clad layers with various overlapping ratios were compared. Then, the alloying element distribution of cladding with a certain overlapping ratio was investigated using EDS and EPMA. As the overlapping ratio increased, the length of the clad decreased and its height increased. In addition, the height of the multi-pass cladding was higher than that of the 1-pass cladding under the same condition. The Fe content of the highly diluted first clad was found to be approximately 20 % in an element analysis. However in the area outside of the first clad, the Fe content was decreased to 10 % as a result of minimum dilution, and a uniform distribution of elements was found.