• Journal of the Optical Society of Korea
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• 제4권1호
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• pp.7-10
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• 2000

The soft x-ray(10nm-100nm) interferometer is a modified Mach-Zehnder type interferometer and it consists of two beam-splitters and four totally reflecting mirrors. The beam-splitters used here are 50% transmission and 50% reflection grating type. The diffraction patterns of beam splitters(1st B.S.) were investigated with a He-Ne laser. The diffraction patterns produced by the soft x-ray interferometer (2nd B.S.) were also investigated in intensities positions. The diffraction patterns of 20 degree grazing incidence on the beam splitters(1st B.S.) show a circular array of spots. Both the reflected and the transmitted beams show the same patterns but symmetric circles on the screen. The maximum intensity appears roughly when n is in the zeroth and odd orders and the suppressed peak(missing order) appears when n is in even orders. Intensities of 3 center fringes(n = 0, $\pm$1) are stronger than others. These results confirm the reduced grating equation and make agree with the intensity distribution function. It was found that the final patterns produced by the soft x-ray interferometer (2nd B.S.) consisted of fine fringes which were caused by two of three diffraction beams that were arrived at the second beam-splitter.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.952-969
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• 2019

This study develops new analytical solutions to water wave diffraction by vertical truncated cylinders in the context of linear potential theory. Three typical truncated surface-piercing cylinders, a submerged bottom-standing cylinder and a submerged floating cylinder are examined. The analytical solutions utilize the multi-term Galerkin method, which is able to model the cube-root singularity of fluid velocity near the edges of the truncated cylinders by expanding the fluid velocity into a set of basis function involving the Gegenbauer polynomials. The convergence of the present analytical solution is rapid, and a few truncated numbers in the series of the basis function can yield results of six-figure accuracy for wave forces and moments. The present solutions are in good agreement with those by a higher-order BEM (boundary element method) model. Comparisons between present results and experimental results in literature and results by Froude-Krylov theory are conducted. The variation of wave forces and moments with different parameters are presented. This study not only gives a new analytical approach to wave diffraction by truncated cylinders but also provides a reliable benchmark for numerical investigations of wave diffraction by structures.

• 한국해안해양공학회지
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• 제2권1호
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• pp.51-57
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• 1990

수심변화가 완만하고 흐름이 없는 곳을 파가 전파할 때 겪게되는 침수, 굴절 및 회절현상의 해석에는 3차 Stokes파 이론에 의한 선형, 비선형, 포물형 방정식이 이용되며, 여기서는 바닥마찰과 바람의 영향은 고려하지 않는다. 이 포물형 방정식으로 암초가 있는 경우에 대해 수치해석을 수행하여 기존의 실험치와 비교 검토하였고, 회절과 굴절효과의 중요성을 고찰했다. 천해파의 특성변화 해석에는 Boussinesq방정식에 기초한 포물형 방정식이 이용된다. 흐름이 없는 경우에 방파제를 따라 전파하는 Cnoidal파의 회절현상을 수심이 변하고 입사각이 변하는 경우에 대해 수치해석을 하여 Stem wave의 특성에 대해 논의하였다.

• 한국수자원학회논문집
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• 제34권6호
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• pp.651-657
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• 2001

본 논문에서는 단파의 파군이 계단형 지형을 통과할 때 발생하는 2차 장파를 이론적으로 연구하였다. 먼저, 수심 변화에 의한 단파의 회절을 해석하였으며, 다변수 섭동법을 이용하여 2차 장파의 지배방정식을 유도하였다. 2차 장파 방정식을 해석하여 서로 다른 속도로 진행하는 자유장파와 구속장파가 발생함을 보였다.

• 한국광학회:학술대회논문집
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• 한국광학회 2002년도 제13회 정기총회 및 2002년도 동계학술발표회
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• pp.104-105
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• 2002

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.644-647
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• 2001

Amorphous As-Ge-Se-S thin films have been studied with the aim of identifying optimum etching condition which can be used to produce holographic grating structure for use as diffractive optical elements. In this study, holographic gratings have been formed using He-Ne laser(632.8nm), and fabricated by the method of wet etching using NaOH etchant with various concentration(0.26N, 0.33N, 0.40N). The diffraction efficiency was obtained by +1st order intensity of the diffracted beam. The formed grating profiles were observed by atomic force microscope and showed that the expected grating profile could be achieved by controlling the etching time. Over-etching resulted in under-cutting of the grating lines. The highest 1st order diffraction efficiency for these gratings was about 5.05%.

• 대한임베디드공학회논문지
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• 제14권6호
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• pp.321-327
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• 2019

Spectral Beam Combining (SBC) is used for a high-power fiber laser in order to overcome the power limitation of single fiber laser. In SBC, several laser bwams with different wavelengths are combined to obtain a single-aperture beam by diffraction grating. The combining efficiency is dependent on a linewidth, beam quality and specific wavelength of each beam among others. In this paper, we consider the method of a wavelength monitoring and a feedback control of laser diodes used as seeds of laser beams to obtain optimum combining conditions. In order to measure the wavelengths of multi-beam, we use the high resolution camera and diffraction grating with 1,800l/mm. The experiment results show the possibility of feedback control of a current and temperature of multi-seed laser diodes to obtain optimum wavelengths for SBC.

• 한국인터넷방송통신학회논문지
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• 제24권2호
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• pp.155-160
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• 2024

편광 선택적 빔 분리 격자는 수많은 광학 정보처리 시스템에서 널리 사용되고 있다. 본 논문에서는 고효율 플라즈마 편광 빔 분리기 (PBS)를 설계하기 위하여 Littrow 구조에서 Ag 금속 층으로 구성된 소자를 구현하였다. 구현한 PBS는 투과되는 0차 TE 편광과 반사되는 0차 TM 편광에서 높은 회절효율을 달성할 수 있도록 격자깊이 및 격자 비율을 정확한 모드 전송선로 이론 (Modal Transmission-Line Theory)을 사용하여 최적화하였다. 최적화된 결과로부터 PBS는 입사 파장과 각도에 대한 광대역 특성의 장점을 가지고 있으며, TE, TM 편광 모두에 대하여 95% 보다 높은 효율을 나타내었다. 그러므로, 높은 흡광비를 갖는 이 고효율 PBS 광대역 격자는 우수한 광 회절 장치로 사용될 수 있다.

• Journal of the Optical Society of Korea
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• 제2권2호
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• pp.58-63
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• 1998

Cross-talk effects in high-density volume holographic interconnections are investigated using perturbative iteration method of the integral form of Maxwell's wave equation. In this method, the paraxial approximation and negligence of backward scattering introduced in conventional coupled mode theory is not assumed. Interaction geometries consisting of non-coplanar light waves and multiple index gratings are studied. Arbitrary light polarization is considered. Systematic analysis of cross-talk effects due to multiple index gratings is performed in increasing level of diffraction orders corresponding to successive iterations. Some numerical examples are given for first and third order diffraction.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.197-197
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• 2009

We have investigated the holographic grating formation on Ag-doped amorphous chalcogenide AsGeSeS thin films with Ag thickness. Holographic gratings have been formed using Diode Pumped Solid State laser (DPSS, 532.0nm) under [P:P] polarized the intensity polarization holography. The diffraction efficiency was obtained by +1st order intensity.