• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.425-428
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• 2009

Silicone is recently used for LED chip encapsulment due to its good thermal stability and optical transmittance. To mold a solid-state silicone encapsulment, curing by mixing at elevated temperatures followed by cooling is necessary. As the silicone molding process is involved in healing and subsequent cooling, the thermal residual stress, which causes mechanical warpage or optical birefringence in the final silicone encapsulment, may be induced if there are non-uniformities in cured silicone material properties or encapsulment shape design. The prediction of residual stress is necessary to design a high-quality silicone molding process. Therefore, in the present paper, a numerical parametric study was attempted to evaluate the heating and cooling effects on the thermal residual stress induced in the cured silicone.

• 한국광학회지
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• 제16권5호
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• pp.456-461
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• 2005

제2조화파 발생용으로 사용되는 볼록평면거울로 구성된 비대칭 불안정 공진기형 Nd:YAG 레이저의 빔질 특성을 수치적으로 분석하였다. 분석은 $M^2$, 공진기 내에서의 빔허리 직경, 모드 부피의 계산을 통해서 이루어 졌다. 수치적 계산 결과는 레이저 헤드가 볼록레이저 거울 근방에 위치한 비대칭 공진기 구조가 될 때 고효율의 제2조화파를 발생할 수 있는 조건이잘 충족됨을 보였다.

• 폴리머
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• 제37권6호
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• pp.744-752
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• 2013

배향된 상태에서 복굴절이 없는 zero-${\Delta}$n 재료를 개발할 목적으로 용융혼합된 폴리락타이드(PLLA, (+)복굴절)/폴리(메틸 메타크릴레이트)(PMMA, (-)복굴절) 블렌드의 상용성과 PMMA의 공단량체인 메틸 아크릴레이트(MA)가 PLLA와의 상용성에 미치는 영향을 살펴보았다. MA 함량에 상관없이 모든 블렌드에서 조성에 따라 변하는 단일 $T_g$와 90% 이상의 투명도가 관찰되었으며, 이로부터 용융혼합된 PLLA/PMMA 블렌드는 분자수준에서 상용성을 보임을 확인하였다. 이들 블렌드는 $280^{\circ}C$의 온도에서도 안정한 단일상을 유지하였다. MA가 17 mol%첨가된 PMMA17과 PLLA의 블렌드의 경우 Hoffman-Weeks 방법을 적용하여 평형융점으로부터 구한 상호작용 에너지 밀도(B)는 $-0.74J/cm^3$이었다. PLLA/PMMA 블렌드는 배향되었을 때 조성고분자들의 고유 배향복굴절이 상쇄되어 특정 혼합비에서 "0" 가까운 복굴절 특성을 나타내었다. PLLA/PMMA5 블렌드의 경우 혼합비에 따른 복굴절 분산을 측정한 결과 zero-${\Delta}$n 특성을 보이는 혼합비에서 역분산이 나타나며, 파장의존성이 없는 복굴절 특성을 보이는 조성이 존재함을 확인하였다.

• Transactions on Electrical and Electronic Materials
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• 제6권2호
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• pp.73-77
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• 2005

In this study, we investigated response characteristics of liquid crystal display (LCD) with different operating mode of nematic liquid crystals (NLCs) such as 45 $^{circ} twisted nematic (TN), 67.3 $^{circ} TN and electrical controlled birefringence (ECB) on the rubbed polyimide (PI) surface with side chains. The pretilt angles generated on polyimide surfaces of the three kinds of LCD operating modes were about 12 $^{circ} that was higher than those of conventional TN-LCOs. Also, the Electro-optical (EO) performance of these LCOs showed stable condition. Low transmittance of the 45 $^{circ} TN and 67.3 $^{circ} TN cell on the rubbed PI surface were measured by using low cell gap d. The fast response time in ECB cell among the three kinds of LCD operating modes was achieved. Also, thermal ability of fast 90 $^{circ} TN-LCD was investigated. The threshold voltage and the response time of thermal stressed TN-LCOs showed the same performances on no thermal stressed TN-LCOs. There was little change of value in these TN cells. However, the transmittances of TN-LCOs on the rubbed PI surface decreased while increasing thermal stress time. Therefore, the thermal stability of TN-LCD was decreased by the high thermal stress for the long duration.

• 폴리머
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• 제26권2호
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• pp.253-259
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• 2002

본 연구는 내열성, 저광학손실 광도파로용 고분자재료를 합성하고 그 물성을 조사한 것이다. 열안정성을 높이고 광학손실을 줄이기 위한 pentafluorophenylmaleimide와 복굴절률을 낮추기 위한 두가지 methacrylate 유도체와 가교제 역할을 하는 glycidylmethacrylate를 삼원 공중합하여 광가교가 가능한 poly(maleimide-co-methacrylate)를 합성하였다. 합성된 고분자들은 높은 열안정성을 나타내었고, 열처리에 의해서 가교가 됨을 확인하였다. 고분자의 굴절율은 공중합 비율에 의해서 조절가능하였고, 1.45~l.49 범위의 고분자가 합성되었다. 복굴절은$6{ imes}10^{-4}$ ~ $1{ imes}10^{-4}$ 범위의 낮은 값을 나타내었다. 이 고분자와 광개시제를 사용하여 접촉 인쇄 방식에 의한 노광과 습식 현상을 통해 깨끗한 광도파로 패턴을 얻을 수 있었다.

• Fibers and Polymers
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• 제5권4호
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• pp.264-269
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• 2004

The present paper deals with improvement in disperse dyeablility as well as imparting of cationic dyeablility to difficultly dyeable polypropylene by a melt blending technique. Isotactic polypropylene (PP) was blended with fibre grade polybutylene terephthalate (PBT), cationic dyeable polyethylene terephthalate (CDPET) and polystyrene (PS), individually. The resulting binary blends were spun and drawn into fibres at draw ratio 2, 2.5, and 3. The compatibility of blends, structural changes of fibres in terms of X-ray crystallinity, relative crystallinity, sonic modulus, birefringence and thermal stability were examined. The blended fibres were found to be disperse dyeable by the conventional method of high temperature and high pressure dyeing. And this dye ability increased with increase in the level of substitution. PP/CDPET blend also exhibited dyeablility with cationic dyes in addition to that with disperse dyes. The optimum level of blending was predicted keeping in view of tenacity and thermal stability of melt blend fibres. The wash fastness properties of the dyed fibres were found to be of high rate.

• Journal of the Optical Society of Korea
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• 제12권4호
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• pp.298-302
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• 2008

We have developed a 270-W 15-kHz MOPA system based on side-pumped rod-type Nd:YAG gain modules. The master oscillator is a 3-W 15-kHz $TEM_{00}$ $Nd:YVO_4$ laser with a pulse duration of 30 ns. To preserve the high beam quality during the amplification, we use image relay and polarization rotation which can simultaneously compensate for thermal lensing and thermal birefringence generated in the rod-type gain modules. After the amplification to 270 W with six rod-type gain modules, the beam quality factor ($M^2$) of the amplified laser beam is 5-10, and the pulse duration is maintained at 30 ns.

• Journal of Information Display
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• 제10권1호
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• pp.19-23
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• 2009

In this paper, we review the proposed liquid crystal display (LCD) with a tunable viewing angle consisting of a conventional liquid crystal display (LCD) panel and a thermally variable retardation layer (TVRL) characterized by uniformly aligned LC film with transparent indium-tin-oxide electrodes for Joule heating. In the TVRL, nematic phase is transitioned into isotropic by Joule heating. The numerical calculation showed that the intrinsic wide viewing angle was achieved at the isotropic phase of the TVRL by Joule heating, whereas the narrow viewing angle was obtained at the nematic phase of the TVRL. The simulated and experimental results of the proposed LCD show continuous and symmetrical viewing angle characteristics by tuning the retardation of TVRL using Joule heating. The structure of the viewing angle control proposed here is adoptable to all LCD modes with wide viewing angle characteristics.

• 대한후두음성언어의학회지
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• 제9권2호
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• pp.147-151
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• 1998

Primary localized laryngeal amyloidosis is an uncommon disorder of unknown cause that occurs in the absence of systemic amyloidosis or associated disease. There is a risk of either missing concomitant systemic amyloidosis or exhaustively investigating for this when it is not present through failure to appreciate the nature of the disease. We present 2 cases of primary localized laryngeal amyloidosis in supraglottic region. Biopsy of the mass of patients revealed findings consistent with amyloidosis, which were Congo red reaction with a apple green birefringence in polarized light fluorescence microscopy. An extensive workup for systemic amyloidosis was negative. All of two cases were treated by vaporization via $CO_2$ LASER using "Swiftlase Flshscan" for creating a wide, shallow char-free treatment site by precisely controlling ablation depth without causing residual thermal damage to tissue. The postoperative recovery of all cases was uneventful with good vocal quality and no aspiration. At the present time, the patients have no evidence of disease, recurrence and complication.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.314-315
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• 2000

레이저 매질은 흡수된 여기 파워에 의해 매질 내부에서 열이 발생하고, 매질 표면을 따라 냉각이 진행되어 매질 내부에서는 불균일한 온도분포가 발생하게 된다.$^{[1,2]}$ 레이저 매질의 굴절율은 온도에 따라 변하기 때문에 열복굴절과 열렌즈 현상이 일어나 레이저 출력의 손실 및 빔질의 저하를 초래하게 된다.$^{[1,3]}$ 선형 편광 광선을 이용하는 고체 레이저는 레이저 매질을 브루스터각으로 가공하거나 공진기 내부쉐 브루스터판을 삽입한다. 따라서, 선형 편광 광선은 열복굴절에 의한 위상 지연으로 타원 편광이 되고, 타원 편광 광선의 s-성분은 브루스터판에서 반사를 일으키게 되어 레이저 출력의 손실을 일으키게 되므로 레이저 공진기를 구성하는데 있어서 정량적인 열영향의 해석이 필요하다$^{[1,2,5]}$ 열영향에 의한 위상 지연은 방위각 방향과 반지름 방향으로 각각 $\Delta$ $n_{\Phi}$, $\Delta$ $n_{r}$ 만큼 생긴 굴절율의 차이로 발생하고 다음과 같이 표현할 수 있다.$^{[1]}$ (중략)이 표현할 수 있다.$^{[1]}$ (중략)