Al₂O₃ 박막의 후처리 효과가 Laser - Induced Damage Threshold에 미치는 영향

유연석(Yeon Serk Yu),이성훈(Seong Hun Lee) 한국광학회 1997 한국광학회지 Vol.8 No.5

Al₂O₃ 박막의 후처리 효과가 laser induced damage threshold에 미치는 영향을 연구하였다. 시료의 증착 온도는 각각 100℃, 200℃, 300℃ 및 350℃로 하여 제작하였고, Nd:YAG 레이저를 이용하여 LIDT를 측정하였다. 제작한 시료는 열처리와 레이저 conditioning으로 후처리한 후 LIDT의 변화를 측정하였는데, 일반적으로 증착 온도를 높게 하여 제작한 시료들에서 LIDT가 높게 측정되었다. 또한 열처리한 경우보다 레이저 conditioning으로 후처리한 경우에서 LIDT는 더 높게 측정되었다. XPS를 사용하여 후처리 전후 박막의 화학 구조적 특성을 측정하였다. The influences of laser-induced damage threshold by the after-processing of Al₂O₃ thin films was investigated. The samples were fabricated at the substrate temperature of 100℃, 200℃, 300℃ and 350℃ respectively, and the LIDT were measured by using Nd:YAG laser. After the processing with baking and laser conditioning of the samples, the variation of LIDT was measured. It was found that LIDT was enhanced twice by laser-conditioning process and 1.5 times by baking process. In addition, we measured the chemical properties of the thin film structure before and after the processing by using XPS.

개구 렌즈 초점에서 폴리크로메틱 광속의 스펙트럼 변화의 실험적 연구

유연석(Yeon Serk Yu) 한국정보기술학회 2009 한국정보기술학회논문지 Vol.7 No.5

The spectral changes of polychromatic spatially coherent gaussian beams focused by an aperture lens in the focal plane is studied based on the propagation law of the cross-spectral density function. The numerical simulation results are presented and the experimental observation results of a spectral changes that take place in the Airy rings formed by diffraction of partially coherent polychromatic light in the focal plane of an aperture lens are presented. The experimental observations show vary similar results with numerical simulation and it is shown that at the critical position U<SUB>c</SUB>, the spectrum is split two lines, while at a position a little smaller than U<SUB>c</SUB>, the spectrum is red-shifted, and at a position a little larger than U<SUB>c</SUB>, the spectrum is blue-shifted. In addition, rapid spectral changes of spatially coherent light may be exploited for information encoding and information transmission in free space optical communications.

프로젝터 보정에 대한 기준 이미지 노이즈의 영향

유연석(Yeon-Serk Yu) 한국정보기술학회 2019 한국정보기술학회논문지 Vol.17 No.2

Projector calibration process is the calculation of projector intrinsic parameters that are based on characteristic point coordinates found by using a checker board image as a reference target. The accuracy of projector calibration depends on the accuracy of the characteristic point coordinate measurements. Here, a secondary calibration was made using the primary calibrated checker board image obtained by the 1st projector calibration. In the 2nd calibration we used a calibrated checker board as the reference image, was added with Gaussian noise at different intensity levels to understand how Gaussian noise influenced to intrinsic parameters by experimentally analyzed. As a result, when the Gaussian noise is 0.25 times the reference image intensity, projector reprojection error, average focal length error, and average principal point error were increased 2.3, 2.1, and 2.3 times, respectively. When the noise intensity is as small as 0.075 times or less, the re-projection error sensitivity to noise is affected by a ratio greater than 1.0.

위상 이동 형상 측정계 위상 에러에 대한 영상 잡음의 영향에 대한 연구

유연석(Yeon-Serk Yu) 한국정보기술학회 2016 한국정보기술학회논문지 Vol.14 No.1

This is an experimental study concerning the effect of image noises on the phase error in phase shifting profilometry which measures 3d profiles using several sinusoidal fringe patterns with different phases. In order to distinguish the effect of image noise on the phase error more clearly, we experimentally measured the phase error values by depending on types and levels of noises through generating gaussian noise and speckle noise on sinusoidal fringe patterns. The each phase of sinusoidal fringe patterns including noises was shifted according to Carré algorithm, displayed on LCD monitor, and captured by CCD camera. The phase were calculated through Carré algorithm and four image data which were captured by CCD camera. When the level of noise is 1.0, the absolute average phase error of gaussian noise is 2.7 times larger than that of speckle noise.

조율 가능한 박막형 광 필터

유연석(Yeon-Serk Yu),임강모(Kang-Mo Lim),이주신(Joo-Shin Lee) 한국정보기술학회 2007 한국정보기술학회논문지 Vol.5 No.2

Optical spectrum switching device and turnable optical filters are key elements for optical networks, spectroscopy and optical sensing. In this work we proposed and analysis the prism type tilt incident optical systems for continuous tuning and optical spectral switching by using the non-micro-electro-mechanical systems. The interference filter air gap is fixed, and wavelength tuning is achieved through scanning the angle of incidence by pre-located rotating prism. The spectral transmittance calculations at different angle of incident show good qualitative agreement with the experimental results. We can get the peak wavelength shift is about 3.7㎚ at 633㎚ by the prism rotations about 1 degree.

In-Situ Pulse Laser Annealing 증착에 의한 광학박막의 표면 개선 효과

이세호,유연석,Lee, Se-Ho,Yu, Yeon-Serk 한국광학회 2009 한국광학회지 Vol.20 No.1

$MgF_2$, $SiO_2$ 및 ZnS 박막을 물리 증기 증착하는 동안 펄스 레이저(Nd-YAG, 제2고조파 532 nm)로 Annealing 하여 표면 거칠기 특성을 개선하였다. 펄스 반복율이 10 Hz, 펄스폭 5 ns, 파장 532 nm인 펄스레이저로 Annealing한 유리 기판에 증착된 $MgF_2$와 $SiO_2$ 시료들은 레이저 에너지가 $140\;mJ/cm^2$ 경우에 산란 총량 값이 최소가 되었지만, ZnS 박막의 경우에는 Annealing 레이저광 에너지가 $62\;mJ/cm^2$일 때 산란 총량이 최소값을 나타냈다. AFM을 사용하여 박막시료의 표면 거칠기에 대한 펄스 레이저 Annealing 효과를 측정 하였다. 그 결과는 TIS 측정치와 유사 하여 표면 거칠기는 Annealing 하기위해 조사된 레이저 에너지에 의존 하여 감소하였다. In-situ pulse laser (Nd-YAG, 2nd harmonics 532 nm) annealing used in physical vapor deposition of $MgF_2$, $SiO_2$ and ZnS thin films was shown to be effective in improving their surface roughness properties. Total integrated scattering (TIS) measurements of $MgF_2$ and $SiO_2$ samples deposited on glass substrates revealed that the laser irradiation of films at an energy of approximately $140\;mJ/cm^2$ at 532 nm with a repetition frequency of 10 Hz and pulse duration of 5 ns during the deposition resulted in total scatterings that were minimum. But in case of the ZnS samples, measurements revealed minimum total scattering at a laser energy of approximately $62\;mJ/cm^2$. Atomic Force Microscopy (AFM) has been used to evaluate the effect of pulse laser annealing on the surface roughness for thin film samples. The results were similar to the TIS measurements, indicating that surface roughness was decreased when the irradiated annealing pulse laser energy increased. But it also increased when the irradiated annealing pulse laser energy was over some limit that depended on the materials.

폴리머 분산 액정의 전기 광학적 스위칭 특성에 대한 액정방울 크기의 효과

김인태,유연석,Kim, In-Tae,Yu, Yeon-Serk 한국광학회 2006 한국광학회지 Vol.17 No.1

폴리머 분산 액정의 전기광학 스위칭 특성에 대한 액정 방울 크기의 효과를 실험적으로 연구하였다. 액정 방울의 크기는 상 분리를 위해 조사하는 레이저 광원의 세기와 LC/oligomer의 혼합 비율에 따라 변화되었다. 전기 광학적 스위칭 전압은 LC/oligomer의 혼합비율과 액정의 방울 크기에 크게 의존하였다. 실험 결과를 보면 상 분리용 조사 레이저광의 세기가 클 때 액정방울의 크기는 작아졌고 포화투과도 전압은 상승했지만 rise time은 짧아 졌다. Effects of liquid-crystal droplets size on electro-optical properties of the polymer dispersed liquid crystals are investigated experimentally The liquid crystal droplets size was varied by controlling the Laser power for phase separation and LC/oligomer composition ratio. Electro-optical switching voltage is dependent on the LC/oligomer composition ratio and liquid crystal droplet size. The experimental results showed droplet size will be small and saturation voltage is increased but rise time will be short at high power illumination laser light for phase separation.

기판의 표면에너지가 반사경의 산란에 미치는 영향

이범식,유연석,이재철,허덕재,조현주,Lee, Beom-Sik,Yu, Yeon-Serk,Lee, Jae-Cheul,Hur, Deog-Jae,Cho, Hyun-Ju 한국광학회 2007 한국광학회지 Vol.18 No.6

ZERODUR와 용융 석영으로 저산란 반사경을 제작하고 산란 특성을 연구하였다. Bowl feed 법을 이용하여 초연마면인 표면거칠기 0.326 ${\AA}$인 용융 석영 기판과 표면거칠기 0.292 ${\AA}$의 ZERODUR 기판을 얻었다. 이온빔 스퍼터링 방법으로 초연마된 기판 위에 $SiO_2$와 $Ta_2O_5$를 교번으로 22층을 증착하여 다층박막 고반사 거울을 얻었다. 용융 석영 반사경과 ZERODUR 반사경의 산란이 각각 4.6 ppm과 30.9 ppm으로 측정되었으며, 이로부터 산란이 매우 작은 경우 기판의 표면거칠기가 산란을 결정하는 주요 파라미터가 아니라는 것을 알았다. 나아가 반사경의 표면거칠기를 AFM으로 측정한 결과. ZERODUR 반사경이 용융 석영 반사경 보다 박막의 표면거칠기가 2.3배 더 높게 측정 되었다. 이 결과는 기판-박막 경계면에서 박막 형성 초기에 기판의 화학조성 또는 결정방향과 증착물질의 상호관계로 인하여 박막 형성 초기에 표면거칠기가 급격히 나빠져서 발생하는 것으로 유추되었다. SEO 300A으로 접촉각 측정을 하여 Giriflaco-Good-Fowkees-Young 방법으로 표면에너지를 계산하였다. 표면거칠기 0.46 ${\AA}$을 갖는 용융 석영 기판이 표면거칠기 0.31 ${\AA}$을 갖는 ZERODUR 기판보다 접촉각이 더 작고 표면에너지는 크게 나타났다. 이러한 차이가 기판 종류에 따라 박막형성 초기에 표면거칠기를 다르게 하는 한 요인으로 판단되며, 기판의 표면에너지가 높을수록 미려한 박막표면을 얻는 것으로 확인되었다. ZERODUR의 표면에너지 차이를 설명하기 위해 XPS 분석으로 용융 석영은 Si, O로 구성되었고 ZERODUR는 Si, O, Al, Na 그리고 F로 구성되었다는 것을 알 수 있었다. Ultra-low loss ZERODUR and fused silica mirrors were manufactured and their light scattering characteristics were investigated. For this purpose, ZERODUR and fused silica substrates were super-polished by the bowl feed method. The surface roughness were 0.292 ${\AA}$ and 0.326 ${\AA}$ in rms for ZERODUR and fused silica, respectively. To obtain the high reflectivity, 22 thin film layers of $SiO_2$ and $Ta_2O_5$ were deposited by Ion Beam Sputtering. The measured light scattering of ZERODUR and fused silica mirror were 30.9 ppm and 4.6 ppm, respectively. This shows that the substrate surface roughness is not the only parameter which determines the light scattering of the mirror. In order to investigate the mechanism for additional light scattering of the ZERODUR mirror, the surface roughness of the mirror was measured by AFM and was found to be 2.3 times higher than that of the fused silica mirror. It is believed that there is some mismatch at the interface between the substrate and the first thin film layer which leads to the increased mirror surface roughness. To clarify this, the contact angle measurements were performed by SEO 300A, based on the Giriflaco-Good-Fowkes-Young method. The fused silica substrates with 0.46 ${\AA}$ in its physical surface roughness shows lower contact angle than that of the ZERODUR substrate with 0.31 ${\AA}$. This indicates that the thin film surface roughness is determined by not only its surface roughness but also the surface energy of the substrate, which depends on the chemical composition or crystalline orientation of the materials. The surface energy of each substrate was calculated from a contact angle measurement, and it shows that the higher the surface energy of the substrate, the better the surface roughness of the thin film.

사각 증착 ITO 박막계의 무반사 및 전자파 차폐 특성

안태균(Tae-Gyun An),유연석(Yeon-Serk Yu) 한국정보기술학회 2014 한국정보기술학회논문지 Vol.12 No.9

If we use OAD method when we coat thin films, the physical and optical properties of thin films are changed as it influences columnar microstruture. When vapor flux incident on substrate surface as oblique angle, thin films grow as porous structure. In this experiment, we fabricated ITO thin films to glass substrate using E-Beam evaporation. The result showed that thin films transmittance and resistivity are increased as vapour fluxs angle of incidence to substrate surface is increased. On the other hand, optical constant is decreased as the angle is increased. Also, we conducted theoretical analysis on electromagnetic wave shielding properties of the oblique angle deposited ITO films using experimental data and found that electromagnetic wave shielding effect was decreased in thin films with large incidence angle. In addition, we designed multi-layer anti-reflection thin films system with using optical constant of oblique angle deposited ITO films and conducted comparative analysis on experimental multi-layer coating data. In conclusion, we could design simplified multi-layer anti-reflection systems having electromagnetic wave shielding property. It is expected to be used as a display device.

변위 측정에 의한 무늬 반사식 형상 측정 시스템의 보정

박병현(Byoung-hyun Park),유연석(Yeon-Serk Yu) 한국정보기술학회 2013 한국정보기술학회논문지 Vol.11 No.1

In this (work) experiments we study the data calibration method of fringe reflection profilometry to measure the shape of specular reflection surface. Fringe reflection FTP calibration data measurements system is consist with CCD camera, monitor, precision moving stage for get the relationship between the phase measurement value and actual height values. The fringe reflection reference surface was moved linearly using the precision stage for the measurement of actual height displacement value and the theoretical simulation data was compared. The calibration data depend on the spatial frequency of the fringe patterns and the geometry of the measurements systems also the angle between the CCD camera and the reference object surface. Using the experimentally measured results we obtained the calibration factor k(u, v) of the each image surface points between the actual height of displacement and the phase measurement values was possible.