• Journal of the Optical Society of Korea
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• 제9권2호
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• pp.49-53
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• 2005

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode (LED) at 650 nm wavelength instead of a laser diode (LD) or He-Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 700 nm and an index precision of $2\times10^{-4}$. To verify the system's capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

• 대한기계학회논문집
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• 제12권3호
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• pp.440-449
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• 1988

본 연구에서는 미소한 진동진폭의 정밀한 측정을 위해 비교적 광선정렬(opti- cal alignment)이 쉽고 광손실이 적으며 국소부위의 진동측정이 가능한 다중반사계를 Michelson간섭계에 도입하였다.미소 진동진폭의 정밀한 값을 결정하기 위해서는 간 섭신호를 측정하여 간섭무늬 보간법과 곡선 맞춤법을 이용하는 방법이 있다. 전자는 간단한 계산과 시간을 절약할 수 있는 반면 후자는 복잡한 계산으로 인해 많은 시간이 소요된다. 그러나 정밀계측장비의 교정에서와 같이 경우에 따라서는 많은 시간과 노 력이 소요되더라도 정밀한 측정결과를 얻어야할 필요가 있기 때문에 이들 두가지 방법 의 정밀도를 확인하기 위해 컴퓨터에 의한 모의실험을 수행하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1307-1311
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• 2007

Three-dimensional transient keyhole profile is numerically analyzed for the case of stationary laser keyhole welding. Volume of fluid (VOF) method is adopted to track the free surface of molten metal based on the three governing equations which are continuity, momentum and energy equations. Multiple reflections of laser beam at the keyhole walls are also included in analysis through a real-time ray tracing technique. In this simulation, especially, polarization of laser is considered as an energy absorption mechanism following the Fresnel reflection theory. Both cases of linearly and circularly polarized beam are simulated and compared. The results show that the theoretically generated keyhole is asymmetrically stretched along the direction of polarization which is already observed experimentally before.

• 전자공학회논문지A
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• 제33A권10호
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• pp.160-167
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• 1996

A new pathlength deviation detection technique which is composed of michelson interferometer is described and verified experimentally. The technique uses a sub-threshold biased visible laser diode of 20$\mu$m coherence length as a low-coherent light source. And for zeroth-order fringe(which is the largest among fringes) identification we used a piezoelectric transducer with a large modulation smplitude, which enables without the need of constant velocity scanning, to distinguish reflection surfaces separated by more than 10$\mu$m with a resolution of less than half-wavelength.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.201-206
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• 2004

Laser scanner are getting used for inspection and reverse engineering in industry such as motors, electronic products, dies and molds. However, due to the lack of efficient scanning technique, the tasks become limited to the low accuracy purpose. The main reasons for this limitation for usefulness are caused from the optical drawback, such as irregular reflection, scanning direction normal to measuring surface, the influence of surface integrity, and other optical disturbances. To overcome these drawback of laser scanner, this study propose the mechanism to reduce the optical trouble by using the 2 kinds of rotational movement axis and by composing the spherical coordinate to scanning the surface keeping normal direction consistently. So, it could be designed and interfaced the measuring device to realize that mechanism, and then it could acquisite the accurate 3D form cloud data. Also, these data are compared with the standard master ball and the data acquisited from the touch point sensor, to evaluate the accuracy and stability of measurement and to demonstrate the implementation of an dental tooth purpose system

• 비파괴검사학회지
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• 제28권1호
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• pp.46-53
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• 2008

복합재료의 내부 결함 평가를 위해 일반적으로 적용되어온 초음파 C-스캔 기법은 섬유자동 배열을 통한 정밀 성형 공정에 적용하기에는 많은 어려움이 있다. 따라서 본 연구는 복합재료의 정밀 성형 공정 중에 발생되는 각종 내부 결함들을 비파괴적, 비접촉으로 평가하기 위한 새로운 하이브리드 초음파 평가 기법을 확립하는데 목적이 있다. 이를 위하여 본 연구에서는 초음파 산란 반사(scattering reflection) 방식을 토대로 한 새로운 이중 피치-캐치(dual pitch-catch) 기법을 확립하여 기존의 결함평가를 위해 시험편의 스캔에 소요되는 시간을 줄이면서 우수한 결함 영상을 얻을 수 있는 새로운 하이브리드 기법을 개발하였다. 즉 두 가지 종류의 열경화성 및 열가소성 복합재료(carbon/epoxy, carbon/PPS) 적층판의 내부 박리(delamination) 결함의 영상화를 위하여 레이저를 이용한 유도 초음파의 발생 및 이중 피치-캐치(pitch-catch)방식을 토대로 한 비접촉식 공기 정합 트랜스듀서(air-coupled transducer)를 이용하여 결함 영상을 얻기 위한 핵심 알고리즘을 확립하였다.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1370-1376
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• 2003

The investigation of liquid fuel film on the cylinder liner is an essential to understand the engine-out hydrocarbon emissions formation in SI engines. In this research, two-dimensional visualization was carried out to investigate the liquid fuel film on the quartz liner in the optical engine. For this, the optical engine with hydraulic system was designed based on the commercial SI engine. The visualization was based on the laser-induced fluorescence with total reflection technique. Using a quartz liner and a special lens, only the liquid fuel film on the liner was visualized. With using this technique, the distribution of the fuel film on the cylinder liner was measured for different engine conditions and injection timing in the optical engine.

• 한국광학회지
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• 제15권1호
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• pp.34-38
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• 2004

파장가변형 광섬유레이저로 광섬유격자 센서어레이를 복조하는 방법을 제안하였다. 레이저의 출력파장을 시간지연 샘플링으로 분석하고 이를 이용하여 기존 시스템의 비선형적 동작특성을 개선하였다. 계산된 파장값은 센서어레이 출력파평의 각 피크에 할당되어 파장가변필터의 비선형성에 영향받지 않고 가해진 물리량에 대하여 항상 선형적인 출력을 얻게 하였다. 실험을 통하여 약 20 pm의 분해능을 얻었으며 이는 고속의 위상변조를 사용할 경우 크게 개선될 수 있음을 보였다.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제4권1호
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• pp.10-21
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• 2001

A new method of laser remote sensing is proposed, based on sensing the sea surface by a narrow laser beam (2-3cm) and analyzing statistically specular reflections. Construction of the angular dependency of the average density of specks versus the aircraft flight horizontal azimuth allows calculation of both intensity and azimuthal properties of the sea surface spectrum. The paper contains the experimental setup and technique, the field measurement data taken onboard an aircraft and the examples of calculated main statistical parameters of sea waves. Their energy-carrying component velocity is found by the mean velocity of an ensemble of specular points at the random sea surface. The surface wave nonlinearity is shown to affect substantially the statistical characteristics measured: mean numbers of specular areas with th given elevation and given slope, arranged along the line of crossing the sea surface by the scanning laser beam. Experimental measurement of a variance in the number of these areas yields a principal possibility to calculate the correlation function of the sea surface without its preliminary modeling.

• 한국정밀공학회지
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• 제4권2호
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• pp.36-46
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• 1987

An optical technique using laser for non-contact measurement of surface roughness and form accuracy of ground surfaces is presented. It is found that, when a ground surface is illuminated by a beam of laser light, the roughness height and slope distribution has significant influence on the pattern of reflection and it maintains an unique Gaussian distribution relationship with the surface roughness. The principle idea of the optical measurement system is therefore monitor the radiation, and then calibrate it in process against surface roughness by means of necessary digital data processing. On the other hand, measuring the form accuracy of a ground surface is accomplished by using a triangular method, which is based on observing the movement of an image of a spot of light projected onto the surface. The image is focused, through a series of lenses for magnification, on a photodetector array lf line configur- ation. Then the relative movement of image and consequently the form accuracy of the surface can be obtained through appropriate calibration procedures. Experimental test showed that the optical roughness measurement technique suggested in this work is very efficient for most industrial applications being capable of monitoring the roughness heights ranging 0.1 to 0.6 .$\mu$m CLA values. And form accuracy can be measured in process with a resolution of 10 .$\mu$m.