• Laser Solutions
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• v.12 no.4
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• pp.17-25
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• 2009

The surface cleaning method based on the laser-induced breakdown (LIB) of gas and subsequent plasma and shock wave generation can remove small particles from solid surfaces. In the laser shock cleaning (LSC) process, a high-power laser pulse induces optical breakdown of the ambient gas above the solid surface covered with contaminant particles. The subsequently created shock wave followed by a high-speed flow stream detaches the particles. In this work, a novel surface cleaning process using laser-induced breakdown of liquid is introduced and demonstrated. LIB of a micro liquid jet increases the shock wave intensity and thus removes smaller particle than the conventional LSC method. Experiments demonstrate that the cleaning force and cleaning efficiency are also increased significantly by this method.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.29 no.1
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• pp.7-20
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• 1999

Magnetic resonance imaging with its superior soft tissue contrast resolution and absence of beam hardening artifacts, combined with its ability to perform multiplanar imaging, is now effective tool in diagnostic imagings. Magnetic resonance is primarily a phenomenon that involves atomic nuclei. It provides totally new clinical informations with no known hazards through the use of very weak interactions with endogenous stable magnetic atomic nuclei. This article briefly summarizes the basic mechanism of generation and detection of the signals and general sorts of tissue properties which can influence the signals and thereby give rise to tissue contrast. It also describes how the machine-operating parameters can be used to manipulate the tissue contrast observed in the image.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.249-251
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• 1994

This paper introduces an implementation of high performance voltage source inverter system based on 16bit micro-processor and DSP for the application to modem rolling stock traction system. In contrast with other industry oriented inverter system, this system requires precise control action complying with various load condition and high overload capability. An asynchronous PWM generation and 3' pulse mode technology are adopted in order to improve compliant starting torque characteristics at starting phase and soft backward-forward starting motion.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.973-979
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• 1995

The input equivalent noise charge (ENC) of hydrogenated amorphous silicon radiation detector diodes was measured and analyzed. The noise sources of amorphous silicon diodes were analyzed into three sources; shot noise, flicker noise and thermal noise from the contact resistance. By comparing the measured ENC with the calculated signal charge in uniform generation case, the signal-to-noise ratio (S/N) for the sample diodes is estimated as a function of the detector bias and the shaping time of Gaussian pulse shaper. The maximum S/N occurred at the bias level just above the full depletion voltage for shaping time of 2∼3 ${\mu}$sec. The developed method is useful in optimum design or amorphous silicon p-i-n diodes for charged particulate radiation spectroscopy.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.12-13
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• 2003

고차조화파를 이용해 아토초 펄스를 생성시킬 수 있음은 최근 여러 연구자들에 의해 이론적으로 제시되어 왔다. 아토초 펄스의 생성은 기본적으로 고차조화파 발생을 이용하여 생성되므로 고차조화파의 연구가 선행되어야 하며, 이에 대한 연구는 이미 많은 연구자들에 의해 이루어 졌다. 초기에 Kulander 등은 Time dependent Schrdinger equation (TDSE) 을사용하여 수치적으로 계산하여 고차조화파의 이론적 분석을 수행하여 단일원자(single atom)에서 발생하는 고차 조화파의 평탄영역(plateau)과 잘림영역(cutoff) 등을 설명하였고, Corkum 등은 준고전적 (semiclassical) 원자 모델을 사용하는 물리적 모형을 제안하여 이 때 계산된 고차조화파가 실험결과 및 완전한 양자역학적 결과와 유사하게 나타남을 보였다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.224-225
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• 2003

Since group velocity (GV) mismatch significantly limits the efficiency of nonlinear interactions such as second harmonic generation (SHG), several techniques have been developed to compensate GV mismatch. The simplest way to avoid the GV mismatch problem is to reduce the device length. However, it results in a poor trade-off between the SHG spectral bandwidth and the conversion efficiency. (omitted)

• Journal of the Optical Society of Korea
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• v.18 no.2
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• pp.151-155
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• 2014

Although various ophthalmic imaging methods, including fundus photography and optical coherence tomography, have been applied for effective diagnosis of ocular diseases with high spatial resolution, most of them are limited by shallow imaging penetration depth and a narrow field of view. Also, many of those imaging modalities are optimized to provide microscopic anatomical information, while functional or cellular information is lacking. Compared to other ocular imaging modalities, photoacoustic imaging can achieve relatively deep penetration depth and provide more detailed functional and cellular data based on photoacoustic signal generation from endogenous contrast agents such as hemoglobin and melanin. In this paper, array-based ultrasound and photoacoustic imaging was demonstrated to visualize pigmentation in the eye as well as overall ocular structure. Fresh porcine eyes were visualized using a real-time ultrasound micro-imaging system and an imaging probe supporting laser pulse delivery. In addition, limited photoacoustic imaging field of view was improved by an imaging probe tilting method, enabling visualization of most regions of the retina covered in the ultrasound imaging.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.236-237
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• 2001

최근 빠른 정보산업의 발달로 대용량의 정보를 초고속으로 전달해야 할 필요성으로 인해 광전송 시스템의 개발이 활발히 진행되고 있다. 특히 광통신 시스템이나 주변의 계측장비들과의 결합이 쉽다는 잇점 때문에 모드록킹된 광섬유 레이저는 이 분야의 광원으로서 매우 중요하게 쓰이고 있으며, 연구가 많이 진행되고 있다. 본 실험에 사용된 광섬유 레이저는 파장 1.55 $mu extrm{m}$대역에서 이득을 얻을 수 있는 어븀(Er$^{3+}$ )이 첨가된 광섬유를 사용하여 4.5 MHz의 빠른 반복률로 모드록킹 되도록 제작된 (Newgrid, (FFL-1550-PML-0) 것이며 펄스 폭은 320 fs, 중심파장은 1.566 $\mu\textrm{m}$, 펄스의 첨두 출력은 6.3 kW이다. (중략)

• Journal of the Optical Society of Korea
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• v.2 no.1
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• pp.9-12
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• 1998

Rational harmonic mode-locking of an Er-doped fiber ring laser has been successfully demonstrated up to the 16-th harmonic, of the RF frequency applied to the electro-optic modulator. This is the highest harmonic reported so far to our knowledge.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.238-239
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• 2001

sub-30fs 펄스폭의 상용 Ti：sapphire 레이저시스템에 대한 펄스압축기 및 2차 조화파 발생기를 제작하여 특성을 평가하였다. 그림la에서 82MHz의 주파수로 모드록되는 상용 Ti：sapphire 레이저 (Spectra-Physics Millennia/Tsunami laser)의 출력이 반사경 Ml, M2를 거쳐 펄스압축기에 입사되고 압축되어 나온 펄스가 다시 M6, M7를 거쳐 2차 조화파발생기로 입사되는 2단구조로 설계되었다. 압축기에 입사되기전 평균파워는 파장 800nm에서 520mW로 측정되었으며, 측정된 스펙트럼 반치폭 47nm에 (그림 2a)에 대해 chirp-free sech$^2$t 펄스로 가정할 경우 본 레이저시스템의 변환한계 펄스폭은 14.5fs로 계산된다. (중략)