• 한국레이저가공학회지
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• 제17권2호
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• pp.19-25
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• 2014

Optical embedded diffraction gratings with the bulk modification in BK-7 glass plates excited by tightly focused high-intensity femtosecond (130fs) Ti: sapphire laser (peak wavelength = 790nm) were demonstrated. The structural modifications with diameters ranging from 400nm to $4{\mu}m$ were photo-induced after plasma formation occurred upon irradiation with peak intensities of more than $1{\times}1013W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred. The maximum refractive index change was estimated to be $1.5{\times}10^{-2}$. The two optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

• 한국결정성장학회지
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• 제14권5호
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• pp.187-192
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• 2004

We try to use isopropanol which has low boiling point to prepare ZnO thin films at low temperature. ZnO thin films were prepared by sol-gel spin-coating method using zinc acetate dehydrate-isopropanol-monoethanolamine (MEA) solution. The c-axis preferred orientation and optical properties of ZnO films with preheating temperature have been investigated. ZnO thin films were preheated at 200 to $300^{\circ}C$ with an interval of $25^{\circ}C$ and post-heated at $650^{\circ}C$. The ZnO film preheated at $275^{\circ}C$ and post-heated at $650^{\circ}C$ was highly oriented along c-axis (002) plane, and the surface with homogeneous and dense microstructures was formed having nano-sized grains. The optical transmittance was above 90 % in the visible range and exhibited absorption edges at 368 nm wavelength.

• 천문학회보
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• 제42권2호
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• pp.88.1-88.1
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• 2017

We report a novel design of the "linear astigmatism-free" three mirror system (LAF-TMS). In general, the linear astigmatism is one of the most dominant aberration degrading image qualities in common off-axis systems. The proposed LAF-TMS is based on a confocal off-axis three mirror system, where higher order aberrations are minimized via our numerical optimization. The system comprises three pieces of aluminum-alloy freeform mirrors that are feasible to be fabricated with current single-point diamond turning (SPDT) machining technology. The surface figures, dimensions, and positions of mirrors are carefully optimized for a LAF performance. For higher precision-positioning mechanism, we also included alignment parts: shims (for tilting) and L-brackets (for decentering). Any possible mechanical deformation due to assembly process as well as 1-G gravity, and its influence on optical performances of the system are investigated via the finite element (FE) analysis. The LAF-TMS has low f-number and a wide field of view, which is promising for sky monitoring programs such as supernova surveys.

• 복식
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• 제22권
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• pp.333-344
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• 1994

In this study an experiment was made using the function of computer simulation os to whether the phenomenon of optical illusion takes place also in clothing on the human body three-dimensional space through the case study of the Gestalt illusion of planar con-traction and expension by amodal completion in perceptual organization. One woman of latter 30s was selected as the experimental subject. She was made to wear the experimental clothing and then the frontal picture was projected of in the experimental clothing which was scanned into the com-puter. For the sake of the contractive experiment 5 stages were divided by 5-15cm the thick-nes of the black vertical line in the center of the upper garmet as the variable and for the sake of the expansive experiment the skirt length was set as the variable. It length measured 50-90cm which was divided by 10cm into 5 stages and simulated using the CAD. The basic design and the experimental de-sign were made one pair and the pictures totalled 20 pictures such as ten pictures save the human body for the estimation of the up-per garmet alone and ten pictures for the ob-servation of the effect on the human body. The extimating panel consisting of 20 panellers estimated contraction/expansion in the estimation of the upper garmet and the tall effect/the slim effect in the estimation of optical illusion as the estimating factors on the 9-point scale. All the date from experiment were analyzed by ANOVA(analysis of variance) and DUNCAN'S multiple range. As a result the experimental designs all showed a significant optical illusion in comparision with the basic design.

• 한국광학회지
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• 제17권2호
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• pp.113-119
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• 2006

망막검사를 위한 검안경용 망막 카메라를 개발하기 위한 광학계 설계를 연구하였다. 이에 앞서 사람의 눈에 대한 광학계 제원은 김상기와 박성찬이 발표한 정밀모형안을 채택하였다. 이를 토대로 하여 광학계를 4개의 렌즈 군으로 구성하였고 제 1군으로 모든 시야각에 대한 광을 중심으로 모았다가 제2, 제3, 제4군에 의해 결상하도록 하였다. 결상된 망막의 상은 CCD 광검출기에 의해 모니터로 전시한다. 제 1군을 단일 렌즈로 하고 나머지 광학계를 triplet로 하여 최적화를 통해 설계하였다. 광선수차, spot diagram, 회절을 고려한 point spread function 및 MTF를 계산하여 분석한 결과, 좋은 성능을 가진 광학계 설계가 가능하였다. 본 연구 결과에서 얻은 광학계로서 양질의 망막 카메라를 개발할 순 있을 것으로 믿는다.

• 천문학회보
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• 제46권2호
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• pp.75.2-76
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• 2021

MESSIER is a science satellite project to observe the Low Surface Brightness (LSB) sky at UV and optical wavelengths. The wide-field, optical system of MESSIER is optimized minimizing optical aberrations through the use of a Linear Astigmatism Free - Three Mirror System (LAF-TMS) combined with freeform mirrors. One of the key factors in observations of the LSB is the shape and spatial variability of the Point Spread Function (PSF) produced by scatterings and diffraction effects within the optical system and beyond (baffle). To assess the various factors affecting the PSF in this design, we use PhoSim, the Photon simulator, which is a fast photon Monte Carlo code designed to include all these effects, and also atmospheric effects (for ground-based telescopes) and phenomena occurring inside of the sensor. PhoSim provides very realistic simulations results and is suitable for simulations of very weak signals. Before the application to the MESSIER optics system, PhoSim had not been validated for confocal off-axis reflective optics (LAF-TMS). As a verification study for the LAF-TMS design, we apply Phosim sequentially. First, we use a single parabolic mirror system and compare the PSF results of the central field with the results from Zemax, CODE V, and the theoretical Airy pattern. We then test a confocal off-axis Cassegrain system and check PhoSim through cross-validation with CODE V. At the same time, we describe the shapes of the freeform mirrors with XY and Zernike polynomials. Finally, we will analyze the LAF-TMS design for the MESSIER optical system.

• 한국태양에너지학회 논문집
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• 제34권3호
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• pp.21-29
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• 2014

Heliostat field control algorithm is the logics to operate the heliostat field of tower type solar thermal power plant and it could include various methodologies of how to control the heliostat field so as to optimize the energy collection efficiency as well as to reduce the system operating cost. This work, as the first part of the consecutive works, presents heliostat aiming mint allocation scheme which will be used in the heliostat field control algorithm for 200kW solar thermal power plant built in Daegu, Korea. We first discuss the structure of heliostat field control system required for the implementation of aiming scheme developed in this work. Then the methodologies to allocate the heliostat aiming points on the receiver are discussed. The simulated results show that the heliostat aiming point allocation scheme proposed in this work reduces the magnitude of peak heat flux on the receiver more than 40% from the case of which all the heliostats in the field aim at the center of receiver simultaneously. Also it shows that, when the proposed scheme is used, the degradation of heliostat field optical efficiency is relatively small from the maximal optical efficiency the heliostat field could have.

• Current Optics and Photonics
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• 제8권1호
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• pp.38-44
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• 2024

Under the influence of atmospheric turbulence, a star's point image will shake back and forth erratically, and after exposure the originally small star point will spread into a huge spot, which will affect the ground calibration of the star sensor. To analyze the impact of atmospheric turbulence on the positioning accuracy of the star's center of mass, this paper simulates the atmospheric turbulence phase screen using a method based on a sparse spectrum. It is added to the static-star-simulation device to study the transmission characteristics of atmospheric turbulence in star-point simulation, and to analyze the changes in star points under different atmospheric refractive-index structural constants. The simulation results show that the structure function of the atmospheric turbulence phase screen simulated by the sparse spectral method has an average error of 6.8% compared to the theoretical value, while the classical Fourier-transform method can have an error of up to 23% at low frequencies. By including a simulation in which the phase screen would cause errors in the center-of-mass position of the star point, 100 consecutive images are selected and the average drift variance is obtained for each turbulence scenario; The stronger the turbulence, the larger the drift variance. This study can provide a basis for subsequent improvement of the ground-calibration accuracy of a star sensitizer, and for analyzing and evaluating the effect of atmospheric turbulence on the beam.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.761-767
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• 1993

A precision planting system using computer controlled technology for mulching cultivation was developed and tested . The system consisting of a micro-computer, several optical fiber sensors and control actuators realized the mechanization of the precision planting operation. The film hole positions, existences of a seed on shutter were detected and the planting speed was measured. The shutter opening mechanism and a seed metering device driven by a stepping motor were controlled, automatically . The planting timing of the shutter opening mechanism were analyzed from a video camera motion analysis, theoretically. The results showed a sufficient accuracy of a seed planted into the center a film hole with a variety of planting speeded. The gravity point positions in film hole of seeds planted by the system just were within the area of +-5mm of the hole center when the hole diameter was 40mm.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.290-290
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• 2006

The toughening mechanisms of polypropylene (PP) containing 9.2 vol % of calcium carbonate ($CaCO_{3}$) nanoparticles were investigated using optical microscopy and transmission electron microscopy. Double-notch four-point bending (DN-4PB) Charpy impact specimens were utilized to study the fracture mechanism(s) responsible for the observed toughening effect. A detailed investigation reveals that the $CaCO_{3}$ nanoparticles act as stress concentrators to initiate massive crazes, followed by shear banding in PP matrix. These toughening mechanisms are responsible for the observed improved impact strength.