• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1535-1542
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• 2001

A high resolution digital cinematic Particle Image Velocimetry(PIV) has been developed. The system consists of a high speed CCD camera, a continuous Ar-ion laser and a computer with camera controller. To improve the spatial resolution, we adopt a Recursive Technique for velocity interrogation. At first, we obtain a velocity vector fur a larger interrogation window size based on the conventional two-frame cross-correlation PIV analysis using the FFT algorithm. Based on the knowing velocity information, more spatially resolved velocity vectors are obtained in the next iteration step with smaller interrogation windows. When the correct velocity vector at the first step is found to be critical, a Multiple Correlation Validation(MCV) technique is applied to decrease the spurious vectors. The MCV technique turns out to improve SNR(Signal to Noise Ratio) of the correlation table. The developed cinematic PIV method has been applied to the measurement of the unsteady flow characteristics of a Rushton turbine mixer. A total of 3,245 instantaneous velocity vectors were successfully obtained with 4 ms time resolution. The acquired spatial resolution corresponds to the conventional high resolution digital PIV system using a 1K ${\times}$ 1K CCD camera.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.863-868
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• 2003

Mixers are used in various industrial fields where it is necessary to intimately mix two reactants in a short period of time. However, despite their widespread use, complex unsteady flow characteristics of industrial mixers are not systematic investigated. The present study aimed to clarify unsteady flow characteristics induced by various impellers in a tank. Impellers arc hydrofoil turbine and neo-hydrofoil turbine types. A high speed CCD camera and an Ar-Ion laser for illumination were adopted to clarify the time-dependent flow characteristics of the mixers. The rotating speed of impellers increased from 6Hz to 60Hz by 6Hz, The maximum velocity around neo-hydrofoil impeller is higher than the hydrofoil type impeller. These two types of turbine shows that typical flow characteristics of axial turbine and suitable for mixing high-viscosity materials.

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.174-180
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• 1996

For the investigation of the influence of microstructure of optical thin films on the in-plane thermal diffusivity of glass substrate coated by that films, we constructed the AC calorimeter which uses argon-ion laser as a thermal source and measured several kinds of ZnS optical thin films which prepared by the changing of thermal evaporation speed such as 5$\AA$/s, 10$\AA$/s, 20$\AA$/s, 40$\AA$/s, 60$\AA$/s. The result showed that the thermal diffusivity decreases as the temperature increases. Also, when the evaporation speed is 20$\AA$/s, the thermal diffusivity has maximum value, and the variation of the thermal diffusivities are 27% at maximum.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.217-217
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• 2011

플라즈마를 이용하는 식각 및 증착등의 반도체공정에 있어서 최근에는 기판의 크기가 점차 증가하는 추세에 있다. 이러한 대면적 플라즈마 발생장치 내에서 플라즈마 밀도와 라디칼 농도의 공간적인 특성을 이해하는 것에 대한 중요성이 더해지고 있다. 이를 위해 Langmuir probe와 같은 전기적 접근법에 의한 진단방법이나 광학적 접근법에 의한 진단방법에 대한 연구가 이루어 졌다. 전기적 접근법에 의한 플라즈마의 진단방법은 원리가 간단하고 정확도가 높다는 장점이 있지만 진단 장치에 의한 플라즈마의 간섭이 크고 식각가스의 경우 진단이 어렵다는 단점이 있다. 그에 비해 광학적 진단방법은 플라즈마에 간섭이 많지 않은 방법으로 알려져 있고 레이저 형광법(LIF), 원적외선 레이저 흡수 분광법(IR laser Absorption Spectroscopy), 광량측정법(Actinometry)등이 있다. 이 중 레이저 형광법, 원적외선 레이저 흡수 분광법의 경우, 진단장치가 매우 복잡하고 가격이 비싸다는 단점을 가지고 있다. 반면 광량측정법의 경우 다른 광학적 접근법에 의한 진단방법에 비해 원리와 실험장치가 간단하고 공간적인 라디칼 분포의 진단이 쉽다는 점에서 장점을 가지고 있다. Actinometry는 Ar과 같은 불활성 기체를 작은 비율을 넣어서 여기 된 불활성 기체의 파장세기와 여기 된 측정 라디칼의 파장세기의 비교를 통해 상대밀도를 측정하는 방법이다. 이 측정 방법에 Abel's inversion equation을 적용함으로 해서 대면적 M-ICP(Magnetized - Induced Coupled Plasma)에서 식각가스인 $CF_4$플라즈마에서 F 라디칼 농도의 공간적인 분포를 측정하고 분석하였다. 또한 플라즈마의 압력, 소스 전력 값과 기판 전력 값등의 조건의 변화에 따라 F 라디칼 농도의 분포가 어떻게 달라지는지에 대해 측정 분석하여 다루었다.

• Korean Journal of Materials Research
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• v.4 no.2
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• pp.233-240
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• 1994

We have investigated how the magneto-optical and recording properties of Pt/Co modulated films vary with sample preparation conditions : sputtering at various gas pressures, sputtering with Xe instead of Ar, and etching the buffer layers, etc. The magneto-optical characteristics of Pt/Co multilayers was comparable with those of currently prevailing rare-earth transition-metal alloys(Tb-Fe-Co amorphous films). On a disk of $12{\times}[Pt10.7\;{\AA}/Co2.8{\;}{\AA}]$ multilayer enhanced with 70nm silicon nitride, we have achieved a CNR of 36dB with a reading laser(${\lambda}\;=\;780nm$) power of 2.5-4.5mW for 720KHz carrier at 1.4m/s and the enhanced kerr rotation angle of $1.23^{\circ}$ at 780nm. It is suggested that Pt/Co modulated films clearly are very promising magneto-optical materials for a commercially use.

• Carbon letters
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• v.1 no.1
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• pp.22-26
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• 2000

Raman spectroscopy has been used to investigate the structure of coal tar pitch heat-treated up to $3000^{\circ}C$ by using 514.5 run Ar ion laser line. Four critical temperature ranges were found on pyrolyzing coal tar pitch, which correspond to four distinct processes from disordered carbons to the well-ordered graphite structure. The range of heat treat temperature (HTT) below $1000^{\circ}C$ corresponds to gas evolution during the pyrolysis of coal tar pitch. Above the HTT are correlated to rearrangements of enlarged molecules, growth of the molecules along the direction of plane, finally stacking in the normal direction of the plane, in the respective HTT ranges of 1000-2000, above 2000 and $2500-3000^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.481-484
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• 2005

Quantum ghost imaging uses quantum mechanically entangled photons to form an image of an object. The quantum ghost image is also obtained by means of classical coincidence measurements with a classically correlated light source[1,2]. In this work we performed classical coincidence imaging experiments with classically correlated beams in their direction of propagation. We observed the ghost interference patterns which were usually made by quantum mechanically entangled states and we also analyze in detail the mechanism of the ghost imaging with classically correlated lights. We made? the classically correlated source with an Ar laser and controlled the direction of the light by a mirror? mounted on a small speaker.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.352-358
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• 1995

Measurements of the Faraday rotation and magnetization of terbium-doped Hoya FR5 glass and cerium-doped Hoya FR4 glass have been made as a function of temperature T in the range 4.2 K -10 K and of magnetic field H of up to 80 kG at the $Ar^+$ laser wavelength of 514.5nm. The saturations of magnetization and Faraday rotation above H/T> $5kG.K^{-1}$ can be analyzed by the quantum theory of paramagnetism. Calculated parameters show that the large Verdet constant of $Ce^{3+}$ glass is due to the effective $4f\rightarrow5d$ electric dipole transition effect and that of $Tb^{3+}$ glass is due to the magnetization effect.effect.

• Journal of Magnetics
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• v.2 no.4
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• pp.147-156
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to a large Kerr rotation angle in the wavelength of a blue laser beam. However, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and a MO recording technology is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, when the Co/Pd mulilayer is used for the MO recording media, changes in the magnetic properties are occurred as the amorphous structure do. Therefore, the assessment of the magnetic properties in the Co/Pd multilayer during interdiffusion is crucially important both for basic research and applications. As the parameter of the magnetic properties in this research, saturation magnetization and perpendicular magnetic anisotropy energy of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. Form the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects the changes in the magnetic properties of the Co/Pd multilayers during the interdiffusion in ferromagnetic state. This discovery will provide the understanding of the magnetic exchange energy in the Co/Pd multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• Journal of Magnetics
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• v.2 no.3
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• pp.86-92
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media in the wavelength of a blue laser beam, due to large Kerr rotation angle. However, since the Co/Pd multilayer is a non-equilibrium state in terms of free energy and MO recording is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, the assessment of the thermal stability in the Co/Pd multilayer is crucially important both for basic research and applications. As the parameter of the thermal stability in this research, effective interdiffusion coefficients (Deff) perpendicular to the interface of the Co/Pd multilayers are measured in terms of Ar sputtering pressure and heat treatment temperature. From the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects Deff of the Co/Pd multilayers. This discovery will provide the understanding of the magnetic exchange energy in the effective interdiffusion process of a magnetic multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.