• 한국광학회지
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• 제5권1호
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• pp.84-89
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• 1994

연속발진 색소레이저를 시드레이저로 하고, Nd:YAG 레이저로 펌핑하는 인젝션 록킹된 단일 모우드 펄스 색소레이저를 제작하였다. 위상민감 검출법으로 얻은 오차신호로 시드빔과 공진 상태를 유지하도록 공진기 길이를 조절하였을 때 99% 이상의 펄스가 시드레이저의 주파수에 록킹 되었다. 이때 레이저 출력빔의 중심 주파수 요동이 10MHz 이내로 안정되었다. 펄스폭(FWHM)은 6ns이고 선폭은 130 MHz이었다. 50mJ로 펌핑하였을 때 2mJ의 출력을 얻었으며 이때의 첨두출력은 0.33 MW이다.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.715-721
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• 2000

Residual stress is one of the causes which makes defects in engineering components and materials. These residual stresses can occur in many engineering structures and can sometimes lead to premature failures. There are commonly used methods by which residual stresses are currently measured. But these methods have a little damage and other problems; therefore, a new experimental technique has been devised to measure residual stress in materials with a combination of electronic laser interferometry, laser heating and finite element method. The electronic laser interferometer measures in-plane deformations while the laser heating and cooling provides for very localized stress relief. FEM is used for determining the heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heat-up and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1588-1595
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• 2000

Natural convection heat transfer in an enclosure with an opening in the right veritcal wall and a heat source at the bottom surface is investigated using a holographic interferometric technique. The effects of the opening length, divider length attached to the top wall, and heater temperature on the temperature distribution are examined. The opening length as well as the divider length greatly affects the degree of inflow and outflow of air. In the case of small opening length, the opening doesnt affect much the upward warm air flow resulting in the symmetric temperature distribution .The upward flow in hindered by the divider resulting in the decrease of heat transfer from the heater region to the upper region. The longest divider shows the highest temperature in the lower region of enclosure. In the case of large opening length, the inward cold flow moves the upward flow to the left direction. Among the cases of different divider length, the case of H(sub)d=0.25H shows the highest temperature in the lower region of enclosure.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1140-1147
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the microscale regime are essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing application, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse(λ=248nm, FWHM=24ns) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of 0.1㎛ and 1m/s, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 연구회
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• pp.189-192
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• 2001

In this paper, an novel optical measuring system based on the electro-optic effect has been proposed and realized using Pockels cell with a view to detecting partial discharge taking place at the needle plane electrode. This system has the following advantages ; nonmetallic probe sensor, immune to external EMI noise and broad band response of the Pockels cell from DC to GHz. This system is constructed by He-Ne laser, Mach-Zehnder interferometer with Pockels sensor, balanced photo receiver, data acquisition board and PC. The response characteristics of the developed proto type sensor are examined for AC and corona discharge.

• KIEE International Transactions on Electrophysics and Applications
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• 제11C권2호
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• pp.6-11
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• 2001

Abstract- In this paper, a new Partial Discharge (PD) detection using Pockels cell was proposed and considerable apparent chaotic characteristics were discussed. For this purpose, PD was generated from needle-plane electrode in air and detecte by optical measuring system using Pockels cell, based on Mach-Zehner interferometer, consisting of He-Ne laser, single mode optical fiber, 50/50 beam splitter and photo detector. In addition, the presence of chaos of the PD signals has been investigated by examining their means of qualitative and quantitative information. For the former, return map and 3-dimensional strange attractor have been drawn in order to investigate the presence of chaotic characteristics relevant to PD signals, detected through CT and Peckels sensor respectively, in the normalized time series. The presence of strange attractor indicates the existence of fractal structures in it's phase space. For the latter, several dimension values of strange attractor were verified sequentially. Throughout this paper, it is likely that the chaotic characteristics regarding the PD signals under air are verified.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.71-76
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• 2005

The defects evaluation of the interior and the surface would be considered as vital characteristics in predicting the total life span of the steel structure. More importantly, the understandings in the interior composite of welding zone and the notifications in the presence, the formation, and the positioning of the non-metallic inclusion are necessary as well, since there were signs of relatively high defect frequency presented in the welding zone. The ultrasonic testing is a highly recommended technique chosen from among other techniques because of variety of advantages in conducting the non-destructive testing for the welding zone. However, the ultrasonic testing had technical disadvantages referred as followings; the problems due to the couplant between the PZT and the specimen, the formations that were miniature and complex, the moving subject, and the high temperature surrounding the specimen. This research was conducted to resolve the technical disadvantages of the contact ultrasonic testing by studying the non-contact ultrasonic testing where the ultrasonic waves were transferred by the laser, and revealing the specimen defects at its interior part and its surface part. The ultimate goal of this research was to develop a non-destructive evaluation applying the laser manipulated ultrasonic method for the steel structure.

• Journal of the Optical Society of Korea
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• 제20권6호
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• pp.784-793
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• 2016

We present a single shot low coherence white light Hilbert phase microscopy (WL-HPM) for quantitative phase imaging of Si optoelectronic devices, i.e., Si integrated circuits (Si-ICs) and Si solar cells. White light interferograms were recorded by a color CCD camera and the interferogram is decomposed into the three colors red, green and blue. Spatial carrier frequency of the WL interferogram was increased sufficiently by means of introducing a tilt in the interferometer. Hilbert transform fringe analysis was used to reconstruct the phase map for red, green and blue colors from the single interferogram. 3D step height map of Si-ICs and Si solar cells was reconstructed at multiple wavelengths from a single interferogram. Experimental results were compared with Atomic Force Microscopy and they were found to be close to each other. The present technique is non-contact, full-field and fast for the determination of surface roughness variation and morphological features of the objects at multiple wavelengths.

• 한국항공우주학회지
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• 제37권6호
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• pp.551-555
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• 2009

본 논문은 광섬유 간섭계의 제한된 회전 측정범위($\pi$/2[radian]) 확장을 통하여 고속 회전입력을 감지할 수 있는 광섬유자이로 설계에 관한 연구 결과를 기술하였다. 디지털 세로다인 변조 기법을 바탕으로 광섬유자이로 신호처리 회로를 설계하였으며, 제작된 프로토타입 광섬유자이로의 시험결과 약 ${\pm}3000[deg/sec]$의 고속 회전측정 성능과 약 150[ppm]의 환산계수 성능을 확인하였다. 따라서 본 논문에서는 고속회전 감지를 위한 광섬유자이로 설계의 유효성이 검증되었다.

• 한국광학회지
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• 제14권3호
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• pp.249-254
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• 2003

본 논문에서는 위상 변조된 가상 영상과 간섭의 원리를 이용하여 영상의 암호화 및 복호화 수준을 향상시키는 방법을 제안하였다. 원 영상은 그레이 값을 가지는 가상 영상과 무작위 암호화 키, 그리고 복호화 키를 위상 변조하여 이들을 간섭계의 한 쪽 경로에 둠으로써 기준파와의 간섭에 의해서 간단히 복원될 수 있다. 제안한 암호화 과정은 원 영상의 어떤 정보도 포함하지 않은 위상 변조된 가상영상과 컴퓨터를 통해서 만들어진 무작위 영상(암호화 키)을 곱함으로써 암호화한다. 그러므로 허가되지 않은 사람들이 암호화키를 분석함으로써 있을 수 있는 복제 가능성을 배제하였다. 또한 그레이 영상을 암호화함으로써 이진 위상 암호화방법에 비해 암호화 수준이 높은 장점을 가진다. 컴퓨터 시뮬레이션과 광 실험을 통하여 제안한 방법이 광 암호화 시스템에 적합함을 확인하였다.