• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.104-108
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• 2004

A simple dispersion measurement technique has been demonstrated by using a self-seeding laser oscillation of a Fabry-Perot laser through a closed loop. The optical pulses of different wavelengths emitted from the Fabry-Perot laser travel down an optical fiber and the group velocity difference between the pulses due to the chromatic dispersion of the optical fiber is measured through the self-seeding laser oscillation process. The dispersion parameter of the optical fiber is calculated from the measured group velocity difference. The performance of the proposed technique has been confirmed experimentally and the accuracy of dispersion parameter measurement was comparable to that of commercial instruments with expensive equipment and components. The repeatability of the proposed method was better than 0.5%.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.20-24
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• 2010

High speed cutting processes of rigid flexible printed circuit board by making use of high power UV laser with nano-second pulse width have been proposed and investigated experimentally. Also robust laser cutting system has been designed and developed in order to obtain a good cutting quality of rigid and flexible PCB with multi-layers (2-6 layers). Power controller module developed for ourselves is adapted to control the laser output power in the range less than 1%. The systems show the good performance of cutting speed, cutting width and cutting accuracy, respectively. Especially we have confirmed that the short circuit problem due to the carbonized contamination occurred in cross section of multi-layers by thermal effect of high power laser has been improved largely by using multi-pass cutting process with low power and high speed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1136-1143
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• 2010

One-way laser ranging technology is applied for the precise orbit determination of LRO, which is the first trial for supporting the missions of lunar or planetary spacecraft. In this paper, LRO payload and ground system are discussed for LRO laser ranging, and some errors effecting on time of flight and tracking mount accuracy are analyzed. Additionally several technologies are also analyzed to make laser pulses shot from ground stations to arrive in the LRO earth window. Measurement data of LRO laser ranging verified that these technologies could be implemented for one-way laser ranging of lunar spacecraft.

• Current Optics and Photonics
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• v.6 no.4
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• pp.381-391
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• 2022

Two-photon-polymerization additive-manufacturing systems feature high resolution and precision. However, there are few reports on specific methods and possible problems concerning the use of small lasers to independently build such platforms. In this paper, a femtosecond-laser two-photon-polymerization additive-manufacturing system containing an optical unit, control unit, monitoring unit, and testing unit is built using a miniature femtosecond laser, with a detailed building process and corresponding control software that is developed independently. This system has integrated functions of light-spot detection, interface searching, micro-/nanomanufacturing, and performance testing. In addition, possible problems in the processes of platform establishment, resin preparation, and actual polymerization for two-photon-polymerization additive manufacturing are explained specifically, and the causes of these problems analyzed. Moreover, the impacts of different power levels and scanning speeds on the degree of polymerization are compared, and the influence of the magnification of the object lens on the linewidth is analyzed in detail. A qualitative analysis model is established, and the concepts of the threshold broadening and focus narrowing effects are proposed, with their influences and cooperative relation discussed. Besides, a linear structure with micrometer accuracy is manufactured at the millimeter scale.

• The korean journal of orthodontics
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• v.50 no.1
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• pp.13-25
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• 2020

Objective: The aim of this study was to compare the accuracy and reliability of measurements performed using two different software programs on digital models generated using two types of plaster model scanners (a laser scanner and a computed tomography [CT] scanner). Methods: Thirty plaster models were scanned with a 3Shape laser scanner and with a Flash CT scanner. Two examiners performed measurements on plaster models by using digital calipers and on digital models by using Ortho Analyzer (3Shape) and Digimodel^® (OrthoProof) software programs. Forty-two measurements, including tooth diameter, crown height, overjet, overbite, intercanine and intermolar distances, and sagittal relationship, were obtained. Results: Statistically significant differences were not found between the plaster and digital model measurements (ANOVA); however, some discrepancies were clinically relevant. Plaster and digital model measurements made using the two scanning methods showed high intraclass coefficient correlation values and acceptable 95% limits of agreement in the Bland-Altman analysis. The software used did not influence the accuracy of measurements. Conclusions: Digital models generated from plaster casts by using laser and CT scanning and measured using two different software programs are accurate, and the measurements are reliable. Therefore, both fabrication methods and software could be used interchangeably.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.1
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• pp.131-147
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• 2020

RFID (Radio Frequency Identification) identifies a specific object by radio signals. As the tag provides a unique ID for the purpose of identification, RFID technology effectively solves the ambiguity and occlusion problem that challenges the laser or camera-based approach. This paper proposes an approach to track a moving object based on the integration of RFID and laser ranging information using a particle filter. To be precise, we split laser scan points into different clusters which contain the potential moving objects and calculate the radial velocity of each cluster. The velocity information is compared with the radial velocity estimated from RFID phase difference. In order to achieve the positioning of the moving object, we select a number of K best matching clusters to update the weights of the particle filter. To further improve the positioning accuracy, we incorporate RFID signal strength information into the particle filter using a pre-trained sensor model. The proposed approach is tested on a SCITOS service robot under different types of tags and various human velocities. The results show that fusion of signal strength and laser ranging information has significantly increased the positioning accuracy when compared to radial velocity matching-based or signal strength-based approaches. The proposed approach provides a solution for human machine interaction and object tracking, which has potential applications in many fields for example supermarkets, libraries, shopping malls, and exhibitions.

• Korean Journal of Geomatics
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• v.2 no.2
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• pp.123-130
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• 2002

LiDAR (Light Detection And Ranging) system has a profound impact on geoinformatics. The laser mapping system is now recognized as being a viable system to produce the digital surface model rapidly and efficiently. Indeed the number of its applications and users has grown at a surprising rate in recent years. Interest is now focused on the reconstruction of buildings in urban areas from LiDAR data. Although with present technology objects can be extracted and reconstructed automatically using LiDAR data, the quality issue of the results is still major concern in terms of geometric accuracy. It would be enormously beneficial to the geoinformatics industry if geometrically accurate modeling of topographic surface including man-made objects could be produced automatically. The objectives of this study are to reconstruct buildings using airborne LiDAR data and to evaluate accuracy of the result. In these regards, firstly systematic errors involved with ALS (Airborne Laser Scanning) system are introduced. Secondly, the overall LiDAR data quality was estimated based on the ground check points, then classifying the laser points was performed. In this study, buildings were reconstructed from the classified as building laser point clouds. The most likely planar surfaces were estimated by the least-square method using the laser points classified as being planes. Intersecting lines of the planes were then computed and these were defined as the building boundaries. Finally, quality of the reconstructed building was evaluated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.949-957
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• 2017

A laser-vision-based height measurement system is developed and implemented for the inspection of two-step variable valve lift module assemblies. The proposed laser-vision sensor module is designed based on the principle of laser triangulation. This paper summarizes the work on 3D point cloud data collection and height difference measurements. The configuration of the measurement system and the proposed height measurement algorithm are described and analyzed in detail. Additional measurement experiments on the height differences of valves and lash adjusters of a two-step variable valve lift module were implemented repeatedly to evaluate the accuracy and repeatability of the proposed measurement system. Experimental results show that the proposed laser-vision-based height measurement system achieves high accuracy, repeatability, and stabilization for the inspection of two-step variable valve lift module assemblies.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.9
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• pp.167-173
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• 2004

The heterodyne He-Ne laser interferometer is the most widely used sensing unit to measure the position error. It measures the positioning error from the displacement of a moving reflector in terms of the wave length. But, the wave length is affected by the variation of atmospheric temperature. Temperature variation of 1$^\circ C$ results in the measuring error of 1ppm. In this paper, for measuring more accurately the position error of the ultra precision stage, the refractive index compensation method is introduced. The wave length of the laser interferometer is compensated using the simultaneously measured room temperature variations in the method. In order to investigate the limit of compensation, the stationary test against two fixed reflectors mounted on the zerodur$\circledR$ plate is performed firstly. From the experiment, it is confirmed that the measuring error of the laser interferometer can be improved from 0.34${\mu}m$ to 0.11${\mu}m$ by the application of the method. Secondly, for the verification of the compensating effect, it is applied to estimate the positioning accuracy of an ultra precision aerostatic stage. Two times of the refractive index compensation are performed to acquire the positioning error of the stage from the initially measured data, that is, to the initially measured positioning error and to the measured positioning error profile after the NC compensation. Although the positioning error of an aerostatic stage cannot be clarified perfectly, it is known that by the compensation method, the measuring error by the laser interferometer can be improved to within 0.1${\mu}m$.

• Journal of KIBIM
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• v.9 no.1
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• pp.11-21
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• 2019

Recently, there is an increase in fire incidents in building structures. Due to this, the importance of fire-damaged buildings' safety diagnosis and evaluation after fire is growing. However, the existing fire-damaged safety diagnosis and evaluation methods are personnel-oriented, so the diagnostic results are intervened by investigators' subjectivity and unquantified. Thus, improper repair and reinforcement can result in secondary damage accidents and economic losses. In order to overcome these limitations, this study proposes using 3D laser scanning technology. The case analysis of fire-damaged building structures was conducted to verify the effectiveness of accuracy and manpowering by comparing the existing method and the proposed method. The proposed method using 3D laser scanning technology to obtain point cloud data of fire-damaged field. The point cloud data and BIM model is combined to inspect the fire-damaged area and depth. From inspection, quantified repair and reinforcement quantity take-off can be acquired. Also, the proposed method saves half of the manpowering within same time period compared to the existing method. Therefore, it seems that using 3D laser scanning technology in fire-damaged safety diagnosis and evaluation will improve in accuracy and saving time and manpowering.