• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.459-463
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• 1996

The lateral-shearing interferometer specially devised for production line inspection lenses is presented. The interferometer is composed with immersion oil and four prisms whose relative sliding motion provide lateral-shearing and phase-shifting. A special phase-measuring algorithm of a-bucket is adopted to compensate the phase-shifting error caused by the thickness reduction in the immersion oil Three different algorithm for determinating quantitative aberration of aspherical lenses are presented and compared with one another.

• 한국주조공학회지
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• 제31권6호
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• pp.354-361
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• 2011

The liquid metal shearing device was constructed and assembled with a commercial high-pressure die-caster in order to induce intensive turbulent shearing force on molten aluminum alloys. The effect of the liquid metal shearing on the microstructure and tensile properties of A356 alloys was investigated with the variation of iron content. The experimental results show that dendritic primary ${\alpha}$-Al phase was effectively modified into a equiaxed form by the liquid metal shearing. It was also found that the needle-like ${\beta}$-AlFeSi phase in a Fe containing A356 alloy was changed into a blocky shape resulting in the improved mechanical properties. Based on the mechanical properties, it was suggested that the iron content in A356 alloy could be more widely tolerated by utilizing the liquid metal shearing HPDC process.

• 비파괴검사학회지
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• 제27권4호
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• pp.321-327
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• 2007

위상잠금 적외선 열화상기법은 넓은 면적을 동시에 검사할 수 있으며, 결함부와 건전부 사이의 위상 차로부터 결함의 유무를 판단할 수 있다. 지금까지 결함의 크기는 검사자의 주관적 판단으로 평가되어 왔으며, 재현성과 정확성이 부족하였다. 본 논문에서는 결함의 크기와 위치 평가에 있어 정확성과 재현성을 개선하기 위해서 전단위상기법을 제안하였다. 시험에서는 인공결함을 갖는 시험편으로 제안된 기법을 검증하였으며, 결함평가에 영향을 주는 인자를 추출하여 그 영향을 분석하였다.

• 비파괴검사학회지
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• 제30권2호
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• pp.91-97
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• 2010

본 연구는 전단위상 위상잠금 적외선열화상기술을 이용한 금속재료 시편의 내부결함을 평가하는 방법에 대한 연구 결과이다. 특히, STS304와 Cu-Zn 시편에 대한 비파괴시험 및 평가는 종래에는 적정한 실험 조건하에서 주로 시행됨에 따라 결항의 형태나 존재를 알 수 없는 상황에서는 최적실험조건을 찾는 일은 오랜 시간이 걸리는 단점이 있었다. 본 연구에서는 위상잠금방볍과 전단위상검출방법을 활용하여 60 MHz 신호로 설정된 가열 조건에서 결함의 위치 및 크기를 평가하였다. 전단위상분포는 시편 내부결함의 크기와 위치를 정량적으로 결정하기 위하여 최대, 최소, 영점을 이용하는 방법이다. 연구 결과로써 인공결함을 갖는 STS 304와 Cu7-Zn3 시험편에 대하여 제안된 기법의 적용을 검증하였으며, 결함평가에 영향을 주는 인자를 추출하고 그 영향을 분석하였다.

• Current Optics and Photonics
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• 제7권6호
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• pp.692-700
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• 2023

We present a method for improving the accuracy of the modal wavefront reconstruction in the radial shearing interferometers (RSIs). Our approach involves expanding the reduced radial terms of Zernike polynomials to high-order, which enables more precise reconstruction of the wavefront aberrations with high-spatial frequency. We expanded the reduced polynomials up to infinite order with symbolic variables of the radius, shearing amount, and transformation matrix elements. For the simulation of the modal wavefront reconstruction, we generated a target wavefront subsequently, magnified and measured wavefronts were generated. To validate the effectiveness of the high-order Zernike polynomials, we applied both low- and high-order polynomials to the wavefront reconstruction process. Consequently, the peak-to-valley (PV) and RMS errors notably decreased with values of 0.011λ and 0.001λ, respectively, as the order of the radial Zernike polynomial increased.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.628-632
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• 2005

Remote sensing through atmospheric turbulence had been hard works for a long time, because wavefront distortion due to the Earth's atmospheric turbulence deteriorates image quality. But due to the appearance of adaptive optics, it is no longer difficult things. Adaptive optics is the technology to correct random optical wavefront distortions in real time. For past three decades, research on adaptive optics has been performed actively. Currently, most of newly built telescopes have adaptive optical systems. Adaptive optical system is typically composed of three parts, wavefront sensing, wavefront correction and control. In this work, the wavefront sensing technology for adaptive optical system is treated. More specifically, shearing interferometers and Shack-Hartmann wavefront sensors are considered. Both of them are zonal wavefront sensors and measure the slope of a wavefront. . In this study, the shearing interferometer is made up of four right-angle prisms, whose relative sliding motions provide the lateral shearing and phase shifts necessary for wavefront measurement. Further, a special phase-measuring least-squares algorithm is adopted to compensate for the phase-shifting error caused by the variation in the thickness of the index-matching oil between the prisms. Shack-Hartmann wavefront sensors are widely used in adaptive optics for wavefront sensing. It uses an array of identical positive lenslets. And each lenslet acts as a subaperture and produces spot image. Distortion of an input wavefront changes the location of spot image. And the slope of a wavefront is obtained by measuring this relative deviation of spot image. Structures and measuring algorithms of each sensor will be presented. Also, the results of wavefront measurement will be given. Using these wavefront sensing technology, an adaptive optical system will be built in the future.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.384-387
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• 1995

Two axes lateral-shearing interferometer(LSI) specially devised for production line inspection lenses is presented. The interferometer composed with four prisms and a dove prism can test the lens performance including asymmetric aspheric lens. The dove prism which rotates the input image with respect to optical axis makes it possible. The wavefront passing through the test lens is reconstsucted by the phase derivative obtained form the two axes LSI system. Zernike-polynomials fitting of this wavefront is presented for determinating quantitative aberration of aspherical lenses.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1845-1852
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• 2001

This paper deals with the experiment to obtain quantitative information about conditions of the interface between a water drop and surrounding oil. Velocity distributions in very close region of the interface are measured by introducing a new illumination technique and a telecentric lens. It enables precise measurements of velocity distributions in the close region to the interface. Although the measured velocity distributions exhibit strong influence from the solid wall of an experimental tube, the coincidence of inner and outside velocities on the interface is clearly confirmed for the clean interface. The shearing stresses on the interface, which are proportional to the velocity gradient normal to the interface, clearly show conditions of contaminated interface, which can be divided into two parts. From front stagnation point to somewhere near a separation point, the distribution of shearing stresses is well coincide with that of the Hadamard's analytical solution, while the distribution on the latter part of the interface sows quite different feature, which is supposed to be strongly influenced by contamination of the surface.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.25-26
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• 2006

The method measuring the absolute position of a point diffraction source emitting a spherical wavefront in three-dimension is proposed. Two-dimensional interference of spherical wavefronts is used to overcome ambiguity of phase order. The spherical wavefront is explicated by Taylor series expansion, from which a radius of curvature of a spherical wavefront and its center position in three-dimension are obtainable. The spherical wavefront is reconstructed by a modified lateral shearing interferometer, which uses single-mode fiber as a point diffraction source.

• 한국광학회지
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• 제8권3호
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• pp.189-193
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• 1997

광 pick-up용 비구면 대물 렌즈는 컴퓨터와 멀티미디어 기기 등의 발달로 수요가 급증하고 있으며 사출성형에 의하여 대량 생산되고 있다. 광 pick-up용 비구면 대물 렌즈의 생산성 향상을 위해서는 생산공정중의 전수검사를 요구하며 이는 측정환경에 강인한 측정기를 필요로 하고 있다. 본 연구에서는 생산공정중에 광 pick-up용 비구면 대물 렌즈를 측정할 수 있는 개선된 층밀리기 간섭계를 제안하고자 한다. 본 층밀리기 간섭계는 3개의 직각 프리즘과 1개의 광분할 코팅된 프리즘으로 구성되며 index matching oil에 의하여 상대이동이 가능하도록 조합되어 있다. 간섭무늬를 정확히 분석하기 위한 위상천이와 층밀림량의 조절은 프리즘 간의 상대 이동에 의하여 가능하며 이를 위한 구동 기구부를 제작하였다. 또한, 본 연구에서는 반복연산에 의한 일반 알고리즘을 도입하여 위상천이 시에 발생하는 index matching oil의 유막 두께변화에 의한 기준위상 오차를 보상하였다. 광 pick-up용 비구면 대물 렌즈의 수차량을 정량적으로 산출하기 위하여 Zernike 다항식 맞춤을 수행하였다. 본 간섭계는 측정환경에 매우 강인하며 방진과 밀폐가 없는 열악한 측정환경하에서 반복측정을 수행하였을 때 .lambda./100 이하의 반복능을 얻었다.