• Current Optics and Photonics
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• 제3권1호
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• pp.72-77
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• 2019

This study was performed to analyze the optical aberrations of the cornea induced by myopic refractive surgery. Corneal total higher-order aberrations, spherical aberration and coma for 4-mm and 6-mm pupils were measured using a wave-front analyzer. The amount of aberrations of the oblate corneal optics by the achieved correction was found to be larger than for the prolate corneal shape with complete eye, in an emmetropia control group. The change in corneal shape acts as an optical factor that degrades the quality of the retinal image; it seems to be one of the important factors related to quality of vision.

• 천문학회보
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• 제38권2호
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• pp.37.1-37.1
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• 2013

We present our study of analyzing the photometric properties of the globular cluster (GC) system which resides in the extended halo of the central bright Coma cluster galaxy NGC 4874. The core of the Coma cluster of galaxies (Abell 1656) was observed with both the HST Advanced Camera for Surveys (ACS) in the F475W (g475) and F814W (I814) and Wide Field Camera 3 IR Channel (WFC3/IR) in the F160W (H160) filters. The data analysis procedure and GC candidate selection criteria are briefly described. We investigate the interesting "tilt" features in color-magnitude diagrams for this GC system and their link to the nonlinear color-metallicity relation for GCs. The NGC 4874's GC system exhibits a bimodal distribution in the optical g475-I814 color and much more than half the GCs fall in the red side at g475-I814 ~ 1.1. This bimodality is weakened in the optical-IR I814-H160 color; the quantitative analysis on the features of both color distributions using the Gaussian Mixture Modeling code proves the bimodalities are different. Both colors, thus, cannot linearly reflect the bimodality of an underlying metallicity, supporting the suggestion that observed bimodalities in extragalactic GC colors are the metallicity-to-color projection effect.

• 천문학회보
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• 제42권1호
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• pp.52.1-52.1
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• 2017

Galaxy clusters are the most massive gravitationally bound systems and thus probably the most recent objects to form. One of promising routes to understand the assembly history of galaxy clusters is to measure observable quantities of components in clusters that are sensitive to the evolutionary state of the cluster. Recent deep observations on the nearby clusters show distinct diffuse intracluster light (ICL), that the light from stars are not bound any individual cluster galaxy, however until now this component has not been well studied due to its faint nature, with typical brightness of ~100 times fainter than the sky background. As shown in galaxy cluster simulation studies, the ICL abundance increases during various dynamical exchanges of galaxies such as the disruption of dwarf galaxies, major mergers between galaxies and the tidal stripping of galaxies. Thus, the ICL is an effective tool to measure the evolutionary stage of galaxy clusters. Moreover, the investigation of the ICL evolution mechanism will allow us understand the galaxy evolution process therein. In this pilot study, we target the Coma cluster, where the existing ICL studies are limited only in the central region. With large and uniform deep optical images from the Subaru telescope, available only recently (Okabe et al. 2014), we are developing a robust ICL measurement technique, extracting the ICL surface brightness and color profiles, which will allow us to study the origin of the ICL and its connection to the evolutionary history of the Coma cluster. For the next phase, we plan to utilize the plenty of spectroscopy data from the MMT telescope to compare ICL properties with the star formation history of the brightest cluster galaxies (BCG), and discuss the ICL formation mechanism of the Coma cluster by comparing the distribution of cluster galaxies with the distribution of diffuse light inside the Coma cluster.

• Journal of the Optical Society of Korea
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• 제19권4호
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• pp.403-408
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• 2015

To evaluate the effects of spherical aberration (SA) correction on optical quality in pseudophakic eyes, we simulated the optical quality of the human eye by computation of the modulation transfer function (MTF). We reviewed the medical records of patients who underwent cataract surgery in Asan Medical Center, retrospectively. A Zywave aberrometer was used to measure optical aberrations at 1-12 postoperative months in patients with AR40e intraocular lens implants. The MTF was calculated for a 5 mm pupil from measured wavefront aberrations. The area under the MTF curve (aMTF) was analyzed and the maximal aMTF was calculated while changing the SA ($-0.2{\sim}+0.2{\mu}m$) and the defocus (-2.0 ~ +2.0 D). Sixty-four eyes in 51 patients were examined. The maximal aMTF was $6.61{\pm}2.16$ at a defocus of $-0.25{\pm}0.66D$ with innate SA, and $7.64{\pm}2.63$ at a defocus of $0.08{\pm}0.53D$ when the SA was 0 (full correction of SA). With full SA correction, the aMTF increased in 47 eyes (73.4%; Group 1) and decreased in 17 eyes (26.6%; Group 2). There were statistically significant differences in Z(3, -1) (vertical coma; P = 0.01) and Z(4, 4) (tetrafoil; P = 0.04) between the groups. The maximal aMTF was obtained at an SA of $+0.01{\mu}m$ in Group 1 and an SA of $+0.13{\mu}m$ in Group 2. Optical quality can be improved by full correction of SA in most pseudophakic eyes. However, residual SA might provide benefits in eyes with significant radially asymmetric aberrations.

• 한국광학회지
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• 제4권1호
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• pp.1-8
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• 1993

축소배율(5$\times$)을 갖고, Seidel 1차 수차중 4개의 비축수차인 코마(coma), 비점수차(astigmatism), 상면만곡(field curvature) 그리고 왜곡수차(distortion)가 제거된 마이크로 리소그라피를 위한 4-구면 반사경 광학계를 해석적으로 구하였다. 이때, $t=d_1+d_2+d_3$<0, (di는 반사거울 $c_i$와 $c_{i+1}$ 사이의 거리)이고, 축상 수차인 구면수차와 잔류고차수차는 반사거울 $c_3$와 $c_4$를 비구면화 하므로서 제거하였다. 이렇게 설계된 4-반사경 광학계의 N.A.는 0.4로서 Rayleigh분해능은 0.38 $\mu\textrm{m}$이다.

• 한국광학회지
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• 제18권1호
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• pp.19-23
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• 2007

원리적인 다양한 장점에도 불구하고 취급이 복잡하고 고차 연립방정식으로 표현되는 현실적 제한으로 인하여 실제 설계과정에서 잘 적용하지 않는 자이델 3차 수차를 이용하여 구한 코마수차 계수식으로부터 근사적인 제로조건을 만족하는 유한 물체거 리를 갖는 코마수차가 제거된 2반사경계의 초기설계에 유용한 곡률선형방정식을 유도하고 그 특징을 조사한다. 즉 주경과 부경의 곡률, 주경과 부경사이의 거리, 유효초점거리로 표현된 변형된 코마수차계수로부터 코마수차계수가 제거되는 조건에서 설계변수를 구하기 위해 전산수치해석 후 나온 데이터를 기반으로 주경과 부경사이의 선형관계가 나타나는 곡률선형방정식을 구하는 것이다. 이는 유한 물점의 코마수차가 보정된 2 반사경계에서 약간의 대수적인 계산만으로 최적화의 초기 입력 데이터를 손쉽게 구할 수 있는 것을 의미한다.

• 천문학회보
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• 제41권1호
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• pp.48.1-48.1
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• 2016

Polarimetric study of light scattering from cometary dust particles can provide us opportunity to decipher their characteristics, such as sizes, structures, compositions of dust grains, etc. Herein, we present the results of our polarimetric study of long-period comet, C/2013 US10 (Catalina), in optical and near-infrared wavelengths which appeared at large phase angle (52.7 degrees) around the mid-December, 2015. We performed polarimetric and spectroscopic observations with HONIR, attached to the 1.5-m telescope at Higashi-Hiroshima Observatory, on UT 2015 December 17-18 and also obtained optical imaging data sets by the Ishigakijima Astronomical Observatory (IAO) and Okayama Astrophysical Observatory (OAO) taken between 2014-2015. By measuring the intensities of gas emission lines with respect to dust continuum and considering transmittance of each filter, we estimated that the percentages of gas contamination are approximately 10 percents in $R_C$-band and 3 percents in $I_C$-band. With these results, we derive the degree of linear polarization scattered solely from dust components in the coma. At this presentation, we will compare the phase-angle dependence of the degree of linear polarization with those of previous archive data in a wide coverage of wavelengths from $R_C$-band to $K_S$-band. Finally, we are supposed to discuss the spatial variations in polarization within the coma.

• 한국광학회:학술대회논문집
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• 한국광학회 1991년도 제6회 파동 및 레이저 학술발표회 Prodeedings of 6th Conference on Waves and Lasers
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• pp.88-89
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• 1991

For the micro-lithography using a KrF excimer laser beam(λ=0.248${\mu}{\textrm}{m}$) a mirror system consisting of four spherical surfaces with reduction magnification 5$\times$ is designed. Initially the aplanat condition of the mirror system is considered. And for the further improved performance of the system the distortion free condition and flat field condition within Seidel 3rd order aberrations are added to the above condition. During the process of designing the computer-aided optimization technique is extensively employed. The spherical aberration, coma, field curvature and distortion of the optimized four-spherical mirror system are removed to the diffraction limit, and residual astigmatism and off-axial vignetting are not corrected enough.

• Journal of the Optical Society of Korea
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• 제10권1호
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• pp.23-27
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• 2006

We are studying the application of an adaptive optics system to upgrade the beam quality of a laser. The adaptive optics (AO) system consists of a bimorph deformable mirror, a Shack-Hartmann sensor and a control system. In most AO applications, the beam aperture is considered to be circular. However, in some cases such as laser beams from unstable resonators, the beam apertures are annulus or a holed-rectangle. In this paper, we investigate how well a bimorph deformable mirror of ${\Phi}120\;mm$ clear aperture can compensate phase distortions for three different beam configurations; 1) ${\Phi}120\;mm$ circular aperture, 2) ${\Phi}100\;mm$ annulus aperture with a ${\Phi}20\;mm$ hole and 3) $70\;mm{\times}70\;mm$ square aperture with a hole of $30\;mm{\times}30\;mm$. This study concludes that the bimorph mirror, which might be considered as a modal controller, can compensate tilt, defocus, coma and astigmatism, and spherical aberration for all three beams.

• Current Optics and Photonics
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• 제1권4호
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• pp.344-350
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• 2017

We present a new design approach and an example design for an image-space telecentric two-mirror system that has a fast f-number and a wide-field line image. The initial design of the telecentric mirror system is a conventional axially symmetric system, consisting of a flat primary mirror with fourth-order aspheric deformation and an oblate ellipsoidal secondary mirror to correct spherical aberration, coma, and field curvature. Even though in the optimized design the primary mirror is tilted, to avoid ray obstruction by the secondary mirror, the image-space telecentric two-mirror system shows quite good imaging performance, for a line imager.